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ureaæ – ureæ
ae – æ
THE
PUERING, BATING & DRENCHING
OF SKINS
_Scientia et potentia humana in idem coincidunt, quia ignoratio
causæ destituit effectum. Natura enim non nisi parendo vincitur: et
quod in contemplatione instar causæ est, id in operatione instar
regulæ est._
Knowledge and human power are synonymous, since the ignorance of
the cause frustrates the effect; for nature is only subdued by
submission, and that, which in contemplative philosophy corresponds
with the cause, in practical science becomes the rule.--BACON,
_Aphorism III_.
THE
PUERING, BATING & DRENCHING
OF SKINS
BY
JOSEPH TURNEY WOOD
DIRECTOR OF TURNEY BROTHERS, LIMITED, NOTTINGHAM;
EXAMINER IN LEATHER TANNING, DRESSING OF SKINS, AND LEATHER DYEING
TO THE CITY AND GUILDS OF LONDON INSTITUTE;
MEMBER OF THE INTERNATIONAL ASSOCIATION OF LEATHER
TRADES CHEMISTS, ETC.
33 ILLUSTRATIONS
[Illustration]
London
E. & F. N. SPON, Ltd., 57 HAYMARKET
New York
SPON & CHAMBERLAIN, 123 LIBERTY STREET
1912
DEDICATED
TO
SIR JOHN TURNEY
THE VETERAN
OF THE
LIGHT LEATHER INDUSTRY
IN
GRATEFUL ACKNOWLEDGMENT
CONTENTS
PAGE
LIST OF ILLUSTRATIONS ix
PREFACE xi
I. DESCRIPTION OF THE PUERING AND BATING PROCESS 1
II. THE CHEMISTRY OF BATING 23
III. THE PHYSICS OF BATING 55
IV. THE BACTERIOLOGY OF THE BATE 87
V. ACTION OF ENZYMES 127
VI. ORIGINAL PAPERS ON BATING 147
VII. ARTIFICIAL BATES 178
VIII. PATENTS 193
IX. DRENCHING 233
X. ORIGINAL PAPERS ON DRENCHING 246
XI. BIBLIOGRAPHY 282
CONCLUSION 292
INDEX 295
ILLUSTRATIONS
FIG. PAGE
1. Curve showing removal of lime by washing 6
2. Cubical “truck” for measuring skin _facing_ 8
3. Puer wheel " 13
4. Front elevation of puer wheel 13
5. End elevation and section of puer wheel 14
6. Sir John Turney’s scudding machine _facing_ 17
7. Curves of ash contents during puering 38
8. Diagram of volumenometer 62
9. " connexions of electrometric apparatus 76
10. Electrometric apparatus 78
11. Apparatus for measuring degree of falling 83
12. Curves obtained by measuring apparatus 85, 86
13. Improved apparatus for measuring degree of falling 86
14. Various forms of bacteria in puer liquors _facing_ 88
15. _B. coli commune_ " 88
16. _B. erodiens_ (Becker) " 97
17. Plate culture from fresh puer " 97
18. " " puer wheel " 103
19. _B. putrificus_ " 103
20. Organisms in pigeon dung, × 1000 104
21. Pure culture of bacillus (_d_) from sweated skin _facing_ 106
22. " " " (_e_) " " " 106
23. _B. butyricus_ (Hueppe) " 112
24. _Spirillum volutans_ (Kutscher), stained to show flagellæ " 112
25. " " " unstained preparation " 112
26. Curves showing rate of hydrolysis 129
27. Organisms in bran drench, × 1000 240
28. Chains of bran bacteria, × 1000 240
29. Bran fermentation, advanced stage 241
30. _B. furfuris_, α _facing_ 269
31. _B. furfuris_, β " 269
32. Cultures of α in glucose gelatin 268
33. Gas curve (_B. furfuris_) 277
PREFACE
The present volume is the outcome of a desire to preserve the numerous
notes which I have made during over twenty years’ work at the practical
and scientific study of bating. It has been my wish to complete the
investigation of this important process in leather manufacture, for,
as Lord Allerton has paradoxically remarked:[1] “Good leather is
made before the skins go into the tan liquor at all,” but owing to
circumstances having drawn me more and more to the commercial side of
the business, I have been compelled to abandon this project.
[1] Report of First Conference of Leather Trade Chemists, 1897,
p. 146.
When learning the trade as an apprentice every fault in the leather was
attributed to this part of the work, and the troubles and miseries of
the “puer shop” first caused me to take up the study of puering. I was
determined to know the causes underlying the process. Puering is not
only a filthy and disgusting operation, but is prejudicial to health,
and in the nature of it is attended by more worry and trouble than all
the rest of the processes in leather making put together.
By giving a résumé of the work done up to the present time, I hope to
be of assistance to the younger generation of Tanning Chemists, to some
of whom is reserved the privilege of carrying on the work.
I think it may now be said, at any rate, that the solution of the
problem of constructing an artificial bate on scientific principles,
which will replace the present crude methods, is well within sight.
The principal obstacles are, on the one hand, the inertia of English
manufacturers; on the other hand, the class of labour employed in
puering is not of the highest order of intelligence. Innovations in
most things are resisted, partly because they necessitate changes in
the method of working, and partly because of the innate conservatism
of human nature. It is certainly a significant fact that although
most of the pioneer work on this subject was done in England, the
practical side has been taken up in Germany, and by freely spending
money on large trials in the works they have enabled the manufacture of
artificial bates to be developed on a commercial scale.
In 1886, while studying Chemistry under Professor Frank Clowes, I
began to examine microscopically the various liquors of a light
leather factory, and more especially the bran drenches. At that time
I knew nothing of bacteriology, for the simple reason that little but
pathological work in this line was being done in England. Through
the kindness of Professor Clowes, I obtained an introduction to Mr.
Adrian Brown (now professor at the University of Birmingham), and in
his laboratory at Burton-on-Trent I saw the first pure cultivations
of _Bacterium Aceti_ which he had isolated, and of which he had
completely studied the chemical action.[2] I had there an opportunity
of seeing the methods and apparatus employed. I also had the benefit
of Mr. Brown’s advice in commencing a systematic study of the process
of drenching. Professor Percy Frankland, then at Dundee, advised me
further as to the microscope and other matters. My warmest thanks are
due to these friends for directing me in the right way.
[2] Jour. Chem. Soc., Mar. 1886.
As a result of my first investigations, on December 11, 1889, I read a
short paper entitled “Methods of Bacteriological Research--with some
account of Bran Fermentation,” before the Society of Chemical Industry.
The way in which this paper was received led to a further research into
the nature of bran fermentation in conjunction with Mr. W. H. Willcox,
B.Sc. (now Senior Analyst to the Home Office), by which the action of
the bran drench was thoroughly investigated, and the results published
in the Journal of the Society of Chemical Industry, May 31, 1893.
This was followed, on June 30, 1897, by a paper “On a Pure Cultivation
of a Bacillus Fermenting Bran Infusions,” also in conjunction with Dr.
Willcox.
In 1898, in reply to a publication of Director Eitner, of Vienna, I
published in the Leather Trades’ Review (November 15), a résumé of the
whole subject, entitled “The Rationale of Drenching.”
Already, in the first paper above named (“Methods of Bacteriological
Research”), I had called attention to the bacteria of the bate prepared
from dogs’ dung, and in a paper entitled “Fermentation in the Leather
Industry,”[3] developed this aspect of the subject, and first pointed
out the influence of enzymes in bating. I therefore decided to study
the phenomena occurring in the bate in the same way as I had studied
drenching.
[3] Jour. Soc. Chem. Ind., 1894. p. 218.
The work was begun in 1895, and, as it was likely to occupy an
indefinite time, the first instalment, entitled “Notes on the
Constitution and Mode of Action of the Dung Bate in Leather
Manufacture,” was published November 30, 1898; while “Further Notes on
the Action of the Dung Bate” was published on November 30, 1899.
In these papers I indicated the lines on which a culture of bacteria
might be practically applied to the bating of skins, and gave the
composition of a liquid which, while acting as a nutrient medium for
the bacteria, contained at the same time most of the active chemical
compounds of dog dung.
Meanwhile, Dr. Popp and Dr. Becker, in Frankfort a/M, were
investigating independently the bacteria of dog dung, and conceived the
idea of employing them commercially. My dear friend Franz Kathreiner,
of Worms,[4] put me in communication with these gentlemen, and we
were thus enabled to work in conjunction. As a result of our combined
labours, an artificial bate, called “Erodin,” was put upon the market.
This will be fully treated of in the chapter on Artificial Bates.
[4] Died, April 1905.
I shall give first a short account of bating, and then sum up as
briefly as possible the present state of our knowledge of the process,
afterwards giving an account of the more important of the various
patents which have been taken out for artificial bates.
Although the book is divided into separate sections for convenience,
it is obvious that we cannot separate chemistry from physics, nor
bacteriology from chemistry, nor enzyme action from all three.
My own papers are printed as read. The Bibliography does not profess to
be complete, but includes most of the works consulted.
No one realizes more than I how incomplete the work is, and how much
research still remains to be done in order to complete it.
Thanks to the efforts of the Leather Industries Department of the
University of Leeds, and the Technical College of the Leather Sellers’
Company, Bermondsey, the era of Rule of Thumb is passing, and there is
little doubt that the work that is being done in these institutions
will be translated into practical use in the factories by the coming
generation.
I wish to express my special thanks to Mr. DOUGLAS J. LAW, and to Dr.
H. J. S. SAND for assistance in preparing the notes for publication,
to Dr. J. GORDON PARKER, Director of the Leather Sellers’ Technical
College, London, for the description of the bating of hides, and to
PROFESSOR KRÀL, of Prague, for some of the photographs of bacteria.
JOSEPH T. WOOD.
Nottingham: _January 1912_.
PUERING, BATING, AND DRENCHING OF SKINS
CHAPTER I.
THE PUERING AND BATING PROCESS.
“Beizen sind Stoffe die mit dem Kalk nicht nur ein chemische
Verbindung einzugehen im Stande sind, wodurch derselbe löslich und
somit vollständig unschädlich wird, sondern auch den gegenseitigen
festen Schluss der einzelnen Wandungen der Zellenelemente
mechanisch lockern, den ganzen Bau der Haut in sich nachgiebiger
machen und so die Verschiebbarkeit der einzelnen Hautgebilde
erhöhen.”--J. C. H. LIETZMANN, 1862.
“Bates are materials which are not only able to enter into chemical
combinations with the lime, whereby it becomes soluble, and is
thereby rendered completely harmless, but they also mechanically
loosen the cementing substance of the separate cell elements, and
render the whole structure of the hide more pliable, and thus
increase the mobility of the various parts.”
The object of bating or puering is to render the skins, and the
resulting leather, soft and supple. Skins which have undergone the
liming process, must be thoroughly freed from lime before going into
the tan liquors, and, for light and soft leathers, they must be reduced
or “brought down,” so that the elasticity or resilience of the skin
fibres is got rid of, and the skin, when tanned, can be stretched
without springing back. This is usually done in the case of light
leathers, by passing the skins through a bate or puer, composed of an
infusion of dogs’ dung in water at a temperature of 35° to 40° C.,
until the required result is obtained. This condition is known to the
workman by the feel of the skin. A good indication is, that the skin
when “down” retains the impression of the thumb and finger if squeezed.
A properly puered skin, when dropped on the floor, will also be
perfectly flaccid, the folds lying closely together. It may, however,
be said that it is only by experience and a kind of instinct that the
exactly correct condition of the skin can be judged.
I know of no very early works on leather manufacture giving an account
of bating. It was a “secret process,” and the results obtained depended
almost entirely upon the judgment of the operator; and this judgment
was frequently in error, owing to the fact that he did not understand
what took place in the bate.
The earliest account I have been able to find is in a book[5] in the
possession of Mr. Seymour-Jones, of Wrexham, entitled “The Art of
Tanning and Currying Leather, with an Account of all the Different
Processes made use of in Europe and Asia for Dying Leather Red and
Yellow, Collected and Published at the Expense of the Dublin Society,
to which are added Mr. Philippo’s Method of Dying the Turkey Leather as
approved of by the Society for the Encouragement of Arts, etc., and for
which he had a Reward of £100, and their Gold Medal, for the Secret.
Also the New Method of Tanning invented by the late David Macbride,
M.D., London. Reprinted for J. Nourse, on the Strand, Bookseller to His
Majesty, 1780.”
[5] There is a copy in the British Museum and also in the Patent
Office Library.
In the chapter entitled “Alumed Calf Skins for Bookbinding” (p. 138),
after the limed skins have been fleshed, the writer continues--
“To alum them, put into a large vat, three or four pails of dogs’ turd
(this dogs’ turd is called alum); on this they fling a large pail of
water to dilute it; this done, the workman goes into the vat, and, with
his wooden shoes, tramples it, filling the vat half full of water. The
_alumer_, on his part, pours water out of his boiler into this vat,
mixing it with the cold water, after which he flings in the skins,
stirring them and turning them for some moments with great sticks.”
The work is described pretty much as now practised, the puer tub being
kept at a uniform heat by constantly taking out liquor, heating it, and
returning it. But neither these goods, nor morocco, are put through a
“drench” _after_ the puer, as we do now; they are scudded on the flesh,
and well washed several times in clear water before being tanned.
*Morocco Leather* (p. 204).--The dry skins are soaked three or four
days, “pared” on the beam, and unhaired in weak lime pits one month.
At Nicosia they put the skins into lime, reduced to powder, for twenty
days in summer, or twenty-five to thirty in winter; out of the lime,
the skins are well washed and drained. The author continues--
“The river work finished, the skins are put into the _dogs’ confit, or
mastering_; for every four dozens of skins they add one bucket of dogs’
excrement, containing fourteen or fifteen quarts, which is worked up
with their hands into a kind of pap and well diluted. The skins are
flung in, stirred and worked in the _mastering_ for some minutes, then
turned and left to rest.
“They remain about twelve hours in the mastering, which opens them,
and takes off the rawness, disposes them to relax, fill and ferment.
This excrement, by its alkaline parts, also cleanses them and takes out
the grease, which would hinder them from taking the colour. I shall
hereafter speak of _bran mastering_.
“At Diarbekir, they make use of these masterings in a different way.
Whilst the skins are drying, they fill great hollows made in the
earth, like our lime pits, with dogs’ dung, which is diluted to the
consistence of honey, or of thin pap, in which they soak the skins for
eight days in winter, and three in summer, treading them each day with
the feet. They are taken out of this fecal matter, and well washed with
fresh water, after which another mastering is made with bran diluted
with water, in which the skins are soaked six days in winter, and three
in summer, observing to tread them each day with the feet, the same as
in the dogs’ mastering; they are then taken out, washed in fresh water,
and prepared for dyeing.”
From these primitive methods the majority of tanners, even of the
present day, have departed but little, except that, instead of stirring
the goods and liquor with a stick, a paddle is used, and the process
thus shortened considerably. Before describing the operation of
puering, it will be best to describe the preliminary washing of the
skins, because, although limed skins may be entered direct into the
puer and brought down quite satisfactorily, in this case more puer and
more time are required, hence it is usual to get rid of the bulk of the
lime by washing them in water before putting them into the puer. In
some cases very dilute hydrochloric or other acid is used, in order to
shorten the time of watering.
It is now well known that lime cannot be entirely removed from skins by
washing in water, no matter how long the washing be continued. A limed
skin containing 4·6 per cent. CaO, calculated on the dry weight, was
found to contain after washing--
-----------+------------------+---------------
Time of | Per cent. CaO on | Per cent. lime
washing | dry skin | removed
-----------+------------------+---------------
1 hour | 3·05 | 34
2 hours | 2·20 | 52
3 " | 1·75 | 62
6 " | 1·55 | 66
7 " | 1·55 | 66
24 " | 1·50 | 67
-----------+------------------+---------------
[Illustration: Fig. 1.]
If the washing be continued, a less amount of lime is removed in each
successive period of time, so that it is evident a point is soon
reached at which it becomes a waste of time to continue the washing.
In practice this point is reached in about two hours. The progress
of the washing is best shown by the curve in the diagram (Fig. 1),
in which the ordinates represent the percentage of lime (CaO) in the
dry skin, and the abscissæ time in hours. It will be seen that the
character of the curve is a hyperbola; such a curve only approaches
a line (representing in the example chosen about 1-1/2 per cent. of
lime) asymptotically--in other words, it is impossible to wash out all
the lime except by an infinite number of changes of water, since each
washing removes a less amount than the previous one. The above is a
typical case of the washing of limed grains from the splitting machine
in the manufacture of skivers. These contain from 4 to 5 per cent. of
lime on the dry skin, and, after washing in water in a paddle for six
hours, analysis shows them to contain still about from 1·5 per cent.
to 1·9 per cent. of lime (CaO).[6]
[6] Some further analyses of grains at Trent Bridge gave the
following results:--
Water CaO CaO on
dry skin
Grain from splitting machines 76·3 1·14 4·8
The same after washing 24 hrs. 86·0 0·22 1·57
The same after puering -- -- 0·80
Another grain 79·7 1·06 5·20
The same after deliming as }
completely as possible with} -- -- 0·45
HCl }
Skin in natural condition 64·0 -- 0·125
M. C. Lamb has found in sheep grains split for skivers the following
amounts:--
Ash CaO CaO in Ash
Grain from splitting machine 9·3 3·2 34·8
The same after washing 4·1 1·5 35·1
The same after puering 3·1 0·9 29·1
The same after bran drench 1·7 0·55 32·4
The figures are all percentages calculated on the dry weight of the
skin.
Munro Payne (Tanners’ Year Book, 1905, p. 75) gives the following
amounts of lime as Ca(OH)_{2} in limed hides, calculated on dry
weight at 212° F.:--
Direct from limes max. 3·859 per cent.
" " min. 2·836 "
Limed for buff 4·621 "
Limed for tanning 3·7659 "
Ditto after bating 0·689 "
Calf limed 2·601 "
Calf bated 0·1215 "
Goat limed 5·613 "
Goat bated 1·268 "
The effect of washing depends on the character of the water (hard or
soft), and also on its temperature. Hard waters should have a small
quantity of clean lime added to them before entering the goods, in
order to remove dissolved CO_{2}, which, by carbonating the lime on
the surface of the skins, renders the grain harsh and the subsequent
puering difficult.
With regard to temperature, it is preferable to employ cold water
until the bulk of the lime is out, since this dissolves more lime than
warm water. 100 c.c. of saturated lime water, at 10° C., contains
0·134 grm. CaO. 100 c.c. at 40° C. contains 0·1119 grm. CaO. Moreover,
a comparatively small rise of temperature causes a considerable
decomposition in a fully limed skin, by which the skin substance is
rendered more soluble, and consequently lost for the purposes of the
tanner. For a fully limed skin the limit of temperature is about 82° F.
(28° C.), whereas a skin free from lime or alkali may be submitted to
a temperature of 120° F. (49° C.) without damage to the fibre. Lamb
prefers a short washing of half an hour in water at 35° to 38° C., for
the reason that the increased temperature causes the goods to become
more flaccid, but this condition is attained at the expense of the loss
of skin substance we have mentioned.
[Illustration: Fig. 2.--Cubical Truck.]
In order to save time and water, the following method is adopted. The
goods are measured by means of a cubical truck on wheels (Fig. 2); it
holds 250 kilos of wet skins (550 lb.). Four of such trucks are placed
in a wash wheel, and a stream of water from a 1-in. pipe turned on. The
goods are run from three-quarters of an hour to one hour; the water is
then stopped, and 4000 c.c. of commercial hydrochloric acid (18° Bé.)
is run in slowly, in a very diluted state, through a perforated lead
pipe. After all the acid has run in, the wheel is run for half an hour,
then water turned on again for half an hour in order to wash away
the calcium chloride produced. During this last washing, hot water is
admitted at the back of the wheel through a perforated pipe, in order
to raise the temperature of the goods, so that they do not enter the
puer wheel in a cold condition, and thus lower the temperature of the
puer liquor. The goods are now ready for puering.
The chemical action of the acid is a very simple one, and is expressed
by the formula--
Ca(OH)_{2} + 2HCl = CaCl_{2} + 2H_{2}O
74 + 73·1 = 110·9 + 36[7]
[7] From the molecular weights it will be seen that 74 grm. of
calcium hydrate, equivalent to 56 grm. of lime (CaO), require 73 grm.
of HCl gas for neutralization. This quantity of gas is contained
in 265 grm. of commercial hydrochloric acid of 18° Bé., or about
230 c.c.--that is, for 100 grm. CaO, 410 c.c. of 18° Bé. acid are
required; hence for the 100 kilos wet grain containing 400 grm. CaO,
1640 c.c. of acid are required for _complete neutralization_. It is
impracticable to use this amount of acid, for the reasons stated
above.
It will be noted that the quantity of acid used is only about one-tenth
of that required to neutralize completely the lime in the skin. If a
greater amount of acid be used the skins begin to absorb acid before
the lime in the interior is neutralized; but, provided the lime on the
surface of the skins is removed, that remaining in the interior is
forced out during the course of the bating process (see Chapter III.).
If more acid were used, then it would require to be added so slowly
that time would be wasted unnecessarily in doing the work.
With regard to the use of other acids for deliming, Lamb considers
formic acid preferable to hydrochloric, and states that the removal
of lime is more effectively accomplished by its use. He attributes
a pulling down action to the calcium formate produced, so that less
formic acid is required than would be equivalent to hydrochloric,
merely regarded as a solvent for lime. We shall refer to this point
again in Chapter II. It may be stated here that the author has obtained
better results by the use of a mixture of formic and acetic acid, in
equal proportions, than from either acid alone, but that the cost of
working is considerably greater than with hydrochloric acid.
Lactic acid is in fairly common use as a deliming agent. In practice
1 per cent. lactic acid (50 per cent. strength) calculated on the wet
weight of pelt, is used, added gradually in small quantities. This does
not remove the whole of the lime, but sufficient for the skins to puer
quickly.
Some tanners measure their acid per dozen skins. In a case which came
under my notice, 1200 c.c. 90 per cent. formic acid were being used for
ten dozens medium goat skins at a temperature of 35° C., time 1-1/4
hours.
The following table, due to Professor H. R. Procter,[8] gives the
cost of dissolving 1 lb. of lime at present approximate prices of
the various acids. The dissociation constant K shows their relative
“strength;”[9] the equivalent, Eq., the weight in lb. of 100 per cent.
acid required to dissolve 28 lb. of lime. Ordinary wet limed hides,
unhaired and fleshed, contain only about 4 lb. lime per 1000 lb. wet
weight.
[8] Tanners’ Year Book, 1911, p. 59.
[9] See Chapter III.
COST OF ACIDS TO REMOVE 1 LB. LIME.
------------+------+-----------+----------+----------+----------
| | | Cost | Strength | Cost for
Acid | Eq. | K | per cwt. | per cent.| 1 lb. CaO
------------+------+-----------+----------+----------+----------
| | | _s. d._ | | _d_.
Hydrochloric| 36·5 | say 200 | 3 3 | 31·5 | 1·4
Sulphuric | 49·0 | " | 4 0 | 95·0 | 0·8
Oxalic | 63·0 | 0·1 | 30 4 | 99·0 | 8·1
Formic | 46·0 | 0·0214 | 35 0 | 87·4 | 7·0
Lactic | 90·0 | 0·0138 | 26 0 | 49·7 | 18·0
Acetic | 60·0 | 0·0018 | 18 0 | 40·0 | 10·0
Butyric | 88·0 | 0·00115 | 21 0 | 82·8 | 8·0
Boracic | 62·0 | 0·00000001| 27 0 | 99·0 | 6·5
------------+------+-----------+----------+----------+----------
It will be seen from the above table that sulphuric is the cheapest
acid to use; but, owing to the insoluble nature of the calcium
sulphate, it is best to use hydrochloric acid. Procter has suggested
using a mixture of sulphuric acid and common salt in molecular
proportions, so as to avoid the iron which is generally present as an
impurity in commercial hydrochloric acid. The author has tried this,
and found it perfectly satisfactory. For a complete discussion of
chemical deliming, see Procter’s “Principles of Leather Manufacture,”
chapter xiii.
Quite recently butyric acid, which is now being manufactured on a
commercial scale by the process of Dr. Effront (Brussels), has come
into use for deliming.[10] and is likely to become a useful acid, as it
can be manufactured cheaply. According to Parker, it dissolves less
skin substance than formic, acetic or lactic acids, which observation
is confirmed by Thuau. The quantity required per 100 lb. of ordinary
washed sheep skin is about 1/2 lb. of the 80 per cent. acid. It is used
in exactly the same way as other acids, i.e. it should be added in
small quantities, suitably diluted, at successive intervals of time.
[10] See also L’Acide Butyrique dans la Tannerie, Urbain J. Thuau, Le
Cuir, Aug. 1910. Also Collegium, 1910, pp. 347, 363.
Acid salts are also used for deliming, and Procter suggested sodium
bisulphate NaHSO_{4} (“Principles,” p. 155). More recently, sodium
bisulphite (NaHSO_{3}) has been recommended;[11] the skins are tumbled
for half an hour with a dilute solution, which combines with the lime
according to the following equation--
(1) Ca(OH)_{2} + NaHSO_{3} = CaSO_{3} + NaOH + H_{2}O
if sulphides are present the reaction is--
(2) Na_{2}S + 2NaHSO_{3} = H_{2}S + 2 Na_{2}SO_{3}
[11] Le déchaulage des Peaux en tripe, Ettore Guisiana (Turin), Coll.
1910, p. 14.
After this treatment the theoretical quantity of hydrochloric acid,
diluted with plenty of water, is run in through the axle of the
tumbler, and the skins run another half hour. The reactions are--
(1) CaSO_{3} + 2HCl = CaCl_{2} + SO_{2} + H_{2}O
(2) Na_{2}SO_{3} + 2HCl = 2NaCl + SO_{2} + H_{2}O
The sulphurous acid evolved in this way slightly swells the skins, and
also removes stains due to the alkaline polysulphides; it is also said
to remove salt stains.
[Illustration: Fig. 3.--Puer Wheel, with Cover Removed.]
[Illustration: Fig. 4.--Elevation of Puer Wheel (back).]
A more interesting process, introduced by Dr. Gr. Eberle[12] as a
bating process, but which is really a deliming process, consists in
using organic acids in the form of their anhydrides, lactones, or
lactides. During the process these anhydrides, lactones, or lactides,
are gradually decomposed with formation of the free acids, which in
a nascent condition unite directly with the lime in the skins. The
anhydrides of acetic, propionic, butyric and lactic acid have been
tried, the lactone of γ-oxybutyric acid
CH_{2} CH_{2}
\
O, and the lactide of lactic acid.
/
CH_{2} CO
[12] Verfahren zum Beizen von Haüten, Ledertechnische Rundschau, No.
24, 1910. Coll. 1910, p. 372.
After washing and deliming, the goods, warmed to a temperature of 90°
to 100° F., are now measured in the truck above described, and put as
quickly as possible into the bating paddle. This is constructed to
carry two trucks. The figures (Figs. 3, 4 and 5) show a modern paddle
adapted for puering light skins, such as goat, sheep, splits (grains),
either with dung or with an artificial bate.
[Illustration: Fig. 5.--End Elevation of Puer Wheel.]
The inside dimensions are: length, 4 ft. 6 in.; width, 4 ft.; depth,
2 ft. 6 in. A copper pipe of two coils is provided at the back,
through which steam is passed for maintaining the temperature of the
wheel--the goods are prevented from coming in contact with this pipe
by a perforated board. Another steam pipe, jointed so that it may be
turned in and out of the paddle, is provided for heating up the wheel
to the required temperature before beginning the bating. This pipe is
not shown in the drawing. The thermometer can be read while the paddle
is in motion. A suitable speed to keep the goods in motion is twenty
revolutions per minute. The whole wheel is covered in, for the purpose
of preserving the heat, and also to exclude light and air, which are
prejudicial to the action of the bacteria. Such a paddle, or wheel,
has a capacity of 200 gallons liquor, or 900 litres, and will bate 25
dozens of average grains, weighing in the wet state 1100 lb. or 500
kilos.
The dog dung, which is usually obtained from hunting kennels, and of
which the composition is given in Chapter II., is simply diluted with
water in the paddle;[13] five buckets, weighing about 165 lb., are
required for the above quantity of goods.[14]
[13] When the puer is dirty it should be diluted with water and
strained through a bag, or the diluted puer may be put into a tub and
the heavy grit and dirt allowed to fall to the bottom of the vessel.
Puer from hunting kennels is usually clean enough to use without this
process.
[14] The quantities of puer used vary considerably in different
works. At Trent Bridge, 10 to 15 lb. of wet puer from hunting kennels
are used per 100 lb. of wet pelt. In a German works, 15 kilos of
fairly dry dog dung are used per 100 kilos of pelt (Blösse). In an
American works, two buckets (one bushel) wet dog dung were used to
puer 10 dozens of 8 lb. calf skins. This is equal to about 62 lb. of
puer to 100 lb. of skin, which seems an excessive quantity. In an
Italian works, two kilos dry dung were used to 20 skins of sheep,
equivalent to about four kilos per 100. In an English tannery,
100 hides for harness leather required four bushels by measure of
pigeon dung, costing 1_s._ 6_d._ per bushel (one bushel equals eight
gallons).
The amount used depends on the state of the goods, the prevailing
weather, and, further, on the quality of the puer.[15] When the
temperature is maintained at 40° C., ordinary limed goods, which have
been washed, come down in from one to three hours.[16]
[15] A German firm, who supply dry dog and pigeon dung for bating
purposes, recommend that the material should be spread in a warm room
at 30° C., and moistened up to 80 per cent. of its weight with an
infusion of oat straw, and continuously turned over until completely
softened. Other materials may be used for the fermenting fluid in
place of the oat straw infusion, such as broth made from waste
fleshings, whey, or even a simple inorganic solution, such as is used
for cultivating bacteria, consisting of--
2 parts potassium phosphate.
1 part magnesium sulphate.
1 part calcium nitrate.
1·5 part calcium chloride.
100 parts water.
This procedure is neither more nor less than an application of the
principles of bacterial cultivation and propagation, shown to be
practically useful in the bating process by Professor H. Becker, of
Frankfort, and by the Author in various publications (see Chapter
VII.).
[16] There is considerable variation in the length of time required
to bring down the skins. Lamb states that half an hour is frequently
sufficient, but at Trent Bridge 2–3 hours are generally required. The
causes of the variation are not altogether clear, but depend partly
on the previous history of the goods (fellmongering, liming, etc.),
and partly on the water used.
During puering, the lime soaps in the skin are decomposed, and the
fat set free--in an estimation of the fat, 0·151 per cent. on the wet
skin was found before puering, and 2·48 per cent. after puering. The
fat thus set free can be removed to a great extent by scudding; but in
modern practice this is not pushed to extremes, as the grain is liable
to be damaged by excessive scudding. The fat is afterwards removed from
the dry leather by means of benzine or other solvent, employed in a
suitable apparatus.
[Illustration: Fig 6.--Sir John Turney’s Scudding Machine for Sheep
Grains.]
*Scudding.*--When the goods are “down,” they are ready for scudding.
This operation in the case of grains is performed either by hand
over the beam, or by means of a special scudding machine.
The scudding machine figured (Fig. 6) was invented by Sir John Turney
in 1880,[17] and is the only type of machine which will safely scud
split skins. It will readily be understood that the usual type of
scudding machine, in which a spiral knife is used, would tear the
delicate structure of the grain. The Turney scudding machine works
with hard, circular brushes, which revolve against a wooden roller
carrying the skin. At the same time a continuous stream of water, at
a temperature of 110° F., is sprayed upon the skins from a perforated
pipe.
[17] The original Turney scudding machine, was invented in 1871,
and patented in that year. The specifications are numbered 1351,
and 3310, 1871. It was also patented in America. Specification No.
131,480, dated September 17, 1872. Improvements in apparatus for
cleaning and scouring hides and skins.
After scudding, the skins are washed in cold water for about ten
minutes. This checks the action of the puer, and also washes away any
loose dirt. They are then ready to pass on to the drench (Chapter IX.),
or to the pickling process, or direct to the tan liquor, according to
the kind of leather required.
*The Bating of Hides for Harness or Dressing Purposes.*--The hides
intended for harness leather, or for dressing purposes, are usually
bated with hen or pigeon manure. The exact process varies in different
tanyards, being dependent upon the condition of the pelt prior to
bating, as to whether it is bated directly after fleshing or receives
a preliminary deliming. The process is also dependent upon the amount
of bating action required for the specific purpose prior to tanning,
but the following three methods are in actual use, and may be taken as
typical methods:--
_Harness Backs._--About a hundredweight of hen manure is put into
a suitable tub or vat capable of holding about fifty gallons; some
thirty gallons of water, at a temperature of about 100° F., is poured
on to the manure, and the whole is thoroughly stirred up by means of
a wooden stick or plunger, working the manure about in order to mix
it to a consistence of thin soup. The vat is now stored in a warm
place, so that the temperature is kept about 70° F.--it is customary to
store this in the boiler-house, or some similar warm room. It should
be stirred two or three times a day, until it begins to show signs of
working; two days is generally sufficient for this.
A pit is now prepared, with the necessary amount of water; and, by the
aid of a steam pipe, or other similar means, the temperature of the
water is raised to 70°, and the contents of the bate tub are now added.
This should be poured into the pit through a sack, or a canvas filter,
so as to keep back stones, solids, feathers, and other extraneous
matters. The pit is now thoroughly plunged, and the goods entered;
these should be handled up three to four times a day for two days. At
the end of two days the goods are usually scudded, by working the back
on an ordinary unhairing beam with an unhairing knife. They then go
into a fresh pit containing a new solution of bate made up in the same
manner, and, when sufficiently bated, which generally takes about three
days, the goods are removed from the pit, scudded again by working them
over with a slate scudding tool, when they are ready for tanning. Some
tanners give them a bath of boracic acid prior to their going into
the tanning liquor; this has the effect of materially brightening the
colour. The second pack of harness backs go into the same liquor--which
must be re-warmed to a temperature of 70°--in which they are handled as
before for about two days, and are finished off in a new liquor made as
above described.
It will be understood, therefore, that in a tanyard, working regularly,
the pack of backs go first into an old bate for two days, and are then
finished off in a freshly made one; so that each pack gets two days in
an old pit, and one or more days in the new. The bate in the tub may
also have a second water, or be strengthened.
_Dressing Hides._--For these goods a somewhat stronger bating effect
is required, and pigeon manure is therefore frequently used. The
preparation of the bating liquor is as described above, both as regards
quantity and temperature of the water and time of maceration.
The whole process may be carried out exactly as described for harness
backs, but the following is an illustration of another method in
practical use. Imagine four ordinary bating pits, worked in a round.
The first pit is very old, having had three packs of hides through it;
the second having had two packs, and the third one pack; and the fourth
is made new. The goods, after unhairing and fleshing, and washing, are
put into the first pit quite cold, are handled in this three times on
the first day, and afterwards put into the second pit, the temperature
of the second pit having been previously raised to 65°--the cold pelt
going into this pit reduces the temperature to about 60°. They are
handled in this pit twice, and remain overnight; and the third day they
go into the third pit, the temperature of which is raised to 70° before
the goods go in. They are raised, scudded thoroughly on the grain,
and new liquor is made from new bating liquor prepared as described
above; the goods are now entered, handled at least twice a day, and,
if insufficiently bated, are left overnight. By the next day they will
probably be sufficiently “down” to permit of them going on to the
scudding beam and thence on to tanning.
In the event of any hide being insufficiently bated--in other words,
if the “bone” has not completely disappeared in the inner part of
the hide--they are returned once more for three or four hours, the
temperature of the pit being raised to 70° with a steam coil.
By this system, which is known as a system of “sets,” it will be
noticed that the pits are worked in a round of four; the first pit,
or oldest, being used more or less as a wash pit, the actual bating
taking place in the second, third and fourth pits. No pit has more
than four packs passing through it, and the temperature never rises
above 70°, or, at the outside, 75°. The reason of the comparatively low
temperature is due to the fact that in pit bating, if the temperature
is raised above 75°, the grain of the hide becomes affected before the
internal “bone” is sufficiently soft, which results in a tender grain,
which considerably affects the resulting staining or dyeing which the
leather usually receives before it is put on the market.
_The Third Process_.--This process is suitable for either harness or
dressing hides, and differs from the above-described process only in
the fact that instead of bating the hides in pits, a latticed drum is
used in order to keep the hides in constant motion. This consists of
a large pit, in which a latticed drum revolves two-thirds immersed in
the liquor. The bate liquor is made up as usual, and the temperature
of the liquor raised to 75° or 80° F.; the hides are then placed in
the latticed drum, which revolves at from four to six revolutions per
minute, and, if the goods are put in the drum in the morning, and
if the temperature is kept at about 70° F., the hides are generally
sufficiently bated by evening. They may then be taken out of the drum,
scudded, and left suspended in boracic acid overnight, and can then be
taken to the liquor next morning.
Where there is considerable motion, even the heaviest hides will stand
a temperature of 75°, and even 80°. Some tanners who use the latticed
drum method, do not place their hides in the drum until the afternoon;
they are drummed for about an hour in the cold bate, and left
overnight; next morning the temperature of the bate is raised to 75°,
and the drum started; they are then removed from the drum towards the
afternoon, when sufficiently “down” to admit of them passing forward
into the next process.
The above are three typical methods in common use in England, but many
modifications of these processes exist. Everything depends upon the
amount of lime in the hide, on the number of haulings or handlings
given to the goods, and the temperature or the conditions under which
the hides are bated, so that no hard-and-fast lines can be laid down.
Much also depends upon the method of liming used, prior to the bating.
It must be borne in mind that the bating of hides, and even of kips,
differs materially from the bating of goat and sheep skins, as one has
to deal with double or even treble the substance. If the bate is worked
at a temperature of even 70° or 75°, there is the danger of the grain
being seriously affected before the bate has penetrated to the interior
of the pelt, unless the goods are kept in constant motion.
Instead of a latticed drum, large paddles are used in some factories.
If the pit is large enough the paddle causes both hides and liquor to
revolve, and thus gives the required movement necessary for a regular
and even “bating effect” to be obtained.
CHAPTER II.
THE CHEMISTRY OF BATING.
“And now, as we cannot understand the _frame_ of a _Watch_, without
taking it into pieces; so neither can Nature be well _known_,
without a _resolution_ of it into its _beginnings_, which certainly
may be best of all done by _Chymical Methods_”--JOS. GLANVILL, 1668.
Professor H. R. PROCTER, in his “Principles of Leather Manufacture,”
1903, p. 153, has given a very complete account of chemical deliming,
and also of the bating and puering processes. Meunier and Vaney, “La
Tannerie,” 1903, give a general review of our knowledge of these
processes up to that date. These accounts are extremely useful, but
treat the subject in a general manner.
I propose to treat of the particular case of puering by means of an
infusion of dogs’ dung in water, as I believe this will give an insight
into all the other bating processes.
So far as the purely chemical action of the bate goes, it consists in
the solution of the lime contained in the skins,[18] thus setting free
a certain portion of skin substance which was combined with the lime,
and the subsequent solution of more or less of this skin substance.
[18] Limed sheep grains, or Pelts, which have been limed for
splitting, contain from 3 per cent. to 6 per cent. CaO on the dry
skin (see footnote, p. 7), and about 80 per cent. of water. In
a typical case of a fully limed grain, the lime was found to be
distributed as follows:--
Free uncombined lime (CaO) 1·7 per cent. on the dry skin
CaO combined with skin 2·5 "
CaO as carbonate, or other salts 1·4 "
-----
5·6
Thus, 75 per cent. of the total lime in the skin was in the caustic
state. If the skin be cut during the progress of the bating
operation, and a solution of phenolphthalein applied to the cut
surface, the course of bating may be followed, and it will be found
that the caustic lime disappears from the skin in a very short
period of time, accompanied by the sudden collapse of the fibres. We
shall treat of this more fully in Chapter III. After puering, the
lime (CaO) contained in the skin, amounts to 0·5 to 0·9 per cent.,
calculated on the dry skin. This lime is in a perfectly neutral
state, and is more or less in combination with the fibre of the skin.
The exact state in which the lime exists in the skin _after_ puering
is not known, and would form a very interesting subject for research.
If a fresh puer be made and boiled for half an hour, then allowed to
cool to 95° F., it will be found to remove the lime from the skin
in a very similar way to an ordinary bate, but it has not so rapid
a reducing action as an unboiled bate. In this case both bacteria
and enzymes are destroyed, so that the action may be put down to the
chemical constituents of the bate.
*Chemical Composition of the Puer.*--The mineral constituents of the
fæces, both in dogs and human beings, are well known, owing to the
study of the processes of digestion and nutrition in physiological
laboratories; but the organic constituents are yet little known, and
the sum of the weight of those at present estimated is far from the
total of these matters present.
It is a mistake to suppose that the fæces represent the residue only
of the food taken. Strassburger[19] estimates that bacteria alone
account for nearly one-third of the dry matter. In addition, the
intestinal mucous membrane is an important excretory channel for lime,
magnesia, iron and phosphoric acid, as has been shown by analyses of
fæces from men and dogs, during prolonged fasting.[20] Even when no
nitrogenous food is eaten, the dry fæces always contain from 4 to 8 per
cent. of nitrogen; in a dog fed on meat it amounts to 6·5 per cent.
[19] Schmidt, and Strassburger, Die Fæces des Menchen (Hirschwald,
Berlin), 1901.
[20] Lambling, Précis de Biochimie, 1911, p. 221.
In making a chemical analysis of the fæces, the mineral matter is
estimated in the ash in the usual way for ash of organic substances,
with special precaution, on account of the phosphates present. The
material is first charred, the salts removed by acetic acid; the acetic
acid solution is then decanted, the residue washed with distilled
water, and the combustion then completed. The acetic solution and
washings are added to the final ash, the whole evaporated to dryness,
and gently ignited to decompose the acetates. (Cf. Bull. 46, U.S. Dept.
of Agriculture, Washington, 1899.)
In estimating the fats, the dry puer is ground up with sand, then
extracted with ether in a Soxhlet. The fats are present in four
states:--1, neutral fats; 2, free fatty acids; 3, alkali soaps, soluble
in ether; 4, small quantities of lime and magnesia soaps remaining
in the residue in the Soxhlet. For details as to the separation and
estimation of these, Lewkowitsch’s “Oils, Fats and Waxes” (Macmillan)
should be consulted.
The separation and estimation of the organic constituents in the puer,
is one of the most difficult problems of physiological chemistry, and
to include the methods used would demand a special treatise beyond the
scope of the present volume. Hoppe-Seyler’s “Physiological Chemistry,”
and Allen’s “Commercial Organic Analysis,” vol. iv., may be consulted;
and there is a mass of useful information in Dr. René Gaultiers’
“Précis de Coprologie Clinique” (Paris, Baillière et Fils, 1907).
It is proposed to give here the results of a number of analyses of dog
dung made by the author and others, and to discuss the action of the
various bodies upon the skins. Many more experiments and much research
requires to be done, before the _complete_ action of the bate is clear,
but only by the method of experiment with the various bodies present
can the problem eventually be solved.
Analysis of raw puer from hunting kennels (Quorn) showed the
approximate composition of 1000 grm. of raw puer, containing 150
grm.[21] of dry matter to be as follows:--
[21] Another sample contained 136 grm. dry matter.
Grammes
Sodium chloride and sodium sulphate 2·1
Sodium ammonium phosphate 14·0
Earthy phosphates, principally Ca_{3}(PO_{4})_{2} 33·6
Ferric phosphate 0·87
Calcium sulphate 1·94
Silicic acid 3·40
Calcium in solution as CaO 1·42
Total P_{2}O_{5} in solution 4·00
Non-volatile acids (as lactic) 3·00
Volatile acids (as acetic) 2·20
Amines (as ammonia) 6·20
Enzymes 3·66
Nitrogenous bodies not included in the above,
consisting of complex amido-acids, leucin,
tyrosin, xanthin, and other purine bases,
indol and skatol 17·00
Organic matter, cellulose, etc. mostly insoluble,
including fats and soaps 70·00
On the dry matter the amounts extracted by various solvents were:--
Per cent.
Water 24·03
Alcohol 22·27
CS_{2} 15·57
C_{2}HCl_{3} (Tri-chlorethylene) 14·45
Petrol. ether 13·23
No carbohydrates (sugars) capable of reducing Fehling’s solution were
found in the puers examined.
The ash[22] of the dry fæces from dogs fed on a flesh diet varies from
20 to 34·27 per cent., with the following percentage composition:--
[22] Gaultier. See also analysis given in Chapter VI.
Silica 7·04
CO_{2} 4·62
SO_{3} 7·37
Fe_{2}O_{3} 4·22
CaO 25·29
P_{2}O_{5} 26·41
MgO 15·52
Cl 1·50
Alkali 5·53
In a dog weighing 30 kilos., fed on a mixed diet of 500 grm. meat and
200 grm. starch, 78·6 grm. dry fæces were obtained containing 23·76 per
cent. ash of the following percentage composition:--
CaO 22·3
P_{2}O_{5} 25·4
Fe_{2}O_{3} 10·6
MgO 9·8
SO_{3} 5·0
Cl 0·2
Alkali 1·1
Insol. in HCl 21·8
It is obvious that the composition of the fæces will vary with the food
given, and in this connexion it may be stated that the puer used was
obtained from dogs fed on a mixture of boiled horseflesh and oatmeal
porridge, about equal quantities. Sometimes charcoal and cabbage are
mixed with the food, in this case the puer is very dark coloured. The
dark colour so produced is to be carefully distinguished from the dark
colour caused by decomposition of the puer.
We cannot leave out of account the urinary products, which, in the case
of dung from hunting kennels, are always present, though in varying
quantities.
The total nitrogen in 1520 c.c. of urine was found[23] to be 15·9 grm.
[23] Abderhalden, Physiological Chemistry.
Each 100 grm. total nitrogen was distributed as follows:--
Urea 85·9
NH_{3} 4·1
Creatinine 3·3
Uric acid 0·5
N in other compounds 5·7
The inorganic compounds were:--
Per cent.
Sulphur (as sulphate) 3·31
P_{2}O_{5} 3·98
Cl 6·30
The urine of carnivora is acid, that of herbivora is neutral or
alkaline.
Urea, which is the chief nitrogenous constituent, is very quickly
fermented by several species of bacteria, and entirely decomposed into
ammonium carbonate, so that it is this latter body which acts in the
bate.
Uric acid exists in the urine of the carnivora, but the quantity is
small compared with the urea. Herbivora excrete, mostly, hippuric acid
NHC, H_{5}O
/
(benzoyl-glycocoll, CH_{2} ),
\
COOH
and this difference may account to some extent for the difference in
bating property, that of the excreta of herbivora being very small as
compared with the carnivora, such as the dog. In this respect there
are differences which are difficult to account for; for instance, the
excreta of the lion, fed entirely on a meat diet, was not found to have
such a powerful bating effect as ordinary dog puer. Even after keeping
for several weeks, to allow the bacterial flora to develop, the result
was the same.
The analysis of the lion’s dung gave the following results:--
Per cent.
Water 59·2
Ash 21·1
Lime (CaO) 10·3
Phosphates (P_{2}O_{5}) 10·67
Organic matter 19·7
Dog dung contains some non-volatile bases of the purine group, such as
xanthin (C_{5}H_{4}N_{4}O_{2}) and guanin (C_{5}H_{5}N_{5}O), but the
action of these bodies in the bate, has not been studied. It is also
extremely probable that these and similar bodies are formed _during_
the bating by a process of auto-digestion of various proteids.[24] The
quantity of _fat_ in dry puer, amounts to 10–11 per cent. Cholesterol
was present.[25] Part of the fat is in the form of lime and magnesia
soaps, but part in the form of an emulsion, which probably plays an
important part in the puering process. The function of the fatty
constituents of puer is one of the problems on which further research
is necessary.
[24] Cf. Mann. Chemistry of the Proteids, 1906, p. 432.
[25] The cholesterol was obtained by extracting the dry puer
with ether, saponifying with alcoholic potash. Shaking out the
unsaponifiables with ether, evaporating to dryness. The residue was
taken up with absolute alcohol, decolorized with animal charcoal.
On cooling, characteristic crystals of cholesterol separated.
Hoppe-Seyler finds from 1 per cent. to 4 per cent. cholesterol in
fæces. See also Gaultier, Coprologie Clinique, p. 160.
The colouring matters of the puer are nearly all derived from bile
products. Most of them are found in the petroleum extract, which
contains far more of the colouring matters than the chloroform extract.
The following bile colouring matters have been prepared by Merck,
of Darmstadt: bilihumin, biliprasin, bilirubin, bilifuscin,
biliverdin.[26] So far as has been ascertained by the author, their
effect in the bating is nil, but, in so far as they impart colour to
the pelt, they are detrimental.
[26] For qualitative tests for the colouring matters, see Gaultier,
Précis de Coprologie Clinique, p. 159.
Experiments on the action of bile are given in the paper reprinted in
Chapter VI.
Recently Eberle[27] has proposed to add a proportion of gall juice
(bile) to a bate containing pancreatic enzymes, with a view of
energizing the latter. This part of the subject will be dealt with in
Chapter V.
[27] English Patent, 21202, 1909. See also Chapter VIII.
*The Reactions of the Puer.*--The organic acids are present principally
in the form of the sodium or calcium salts. The intestinal juices
contain sodium carbonate, but this is neutralized by lactic acid found
in the intestines, so that the excreta usually have an acid reaction.
The reaction of a fresh puer liquor is faintly acid to litmus, but
this acid is immediately neutralized by the introduction of the skins,
so that the rest of the bating process takes place in a neutral or
alkaline medium, and the quantity of lime removed by the free acids is
probably small.
The acidity of a filtered puer liquor made up freshly and titrated with
N/5 soda, and phenolphthalein as indicator, was found to equal 10 c.c.
N/1 acid per 1000 c.c. of bate. In the volume of liquor used, namely,
900 litres, this would neutralize only 250 grm. of lime (CaO).
The determination of the exact acidity or alkalinity of puer liquors
by ordinary methods with indicators is not easy, as the end reactions
are not sharp. The liquor above described was alkaline to methylorange
and litmus, although acid to phenolphthalein, and the results also vary
somewhat, according to the quantity of bate used for titration, and
according to the strength of the acid or alkali used. The method used,
both at the Trent Bridge laboratory and Messrs. Doerr and Reinhart’s
laboratory at Worms, is as follows:--
The puer liquor is filtered through a Schleicher and Schulls hard
filter, No. 602, 18-1/2 cm. diam.; 50 c.c. are taken, 4 drops of
phenolphthalein solution (10 gr. dissolved in 300 c.c. alcohol) added,
and titrated with N/5 acid or alkali as the case may be.
If the acidity be determined by adding excess of alkali and titrating
back, a larger amount of acid is found than by direct titration. In the
above-mentioned case, an indirect titration showed an acidity equal to
18 c.c. N/10 acid per 100 c.c. of liquor.
On adding the alkali to a fresh filtered puer liquor, a flocculent
precipitate is produced, which appears to be due to the decomposition
of proteid compounds of weak organic acids,[28] the alkali uniting with
them and setting the proteids free. As these compounds are undoubtedly
decomposed by the lime in the skins, it seems probable that the acidity
available for neutralizing lime may be greater than that shown by
direct titration.
[28] Probably syntonin, or bodies of a similar nature (see Allen.
Comm. Org. Anal. iv. p. 4). The supposition is supported by the
fact that solutions of puer have a slight laevorotatory action on
polarized light.
See also note on Van Liers paper, Coll. 376, 1909, p. 823.
A method which was suggested by me for the estimation of the acidity
of tan liquors may be applied also to the examination of the bate
liquors, namely, the method by which the electric potential between a
hydrogen electrode dipping into the bate liquor, and a standard calomel
electrode, is used to determine the neutral point (for details see
Chapter III.), using the potentiometer devised by Dr. H. J. S. Sand.[29]
[29] See paper entitled, “The Employment of the Electrometric Method
for the Estimation of the Acidity of Tan Liquors,” by H. J. S. Sand,
Ph.D. D.Sc., and D. J. Law, B.Sc. F.I.C., J.S.C.I. 1911, p. 3; also
Part II., by Wood, Sand and Law, J.S.C.I. 1911, p. 872.
Puer liquors, titrated in this manner with N/10 soda or HCl until a
potential of 0·69 volts is reached (at which point phenolphthalein
turns from colourless to red), gave the following results per 100 c.c.
filtered liquor.
---+-----------------+--------+---------------------------------
| | | {Alkali}
No.| Description of |Reaction|c.c. N/10 { or } Required for
| Liquor | | { Acid } Neutralization
---+-----------------+--------+---------------------------------
1 |{New puer }| Acid | 7·4 alkali
|{before goods }| |
| | |
2 |{The same after }|Alkaline| 0·57 acid
|{goods }| |
| | |
3 |{New puer }| Acid | 8·1 alkali
|{before goods }| |
| | |
4 |{The same after }|Alkaline| 3·25 acid
|{goods }| |
| | |
5 |{Used puer after}|Alkaline| 5·00 acid
|{goods }| |
| | |
6 |Spent puer |Alkaline| 6·6 acid
---+-----------------+--------+---------------------------------
Determinations made in this way are more accurate than the colorimetric
method above described. Puer liquors after use are found by the
electrometric method generally on the alkaline side, whereas such
liquors show neutral to phenolphthalein owing to some action of the
bate constituents on the indicator.
PUER LIQUORS IN ELECTROMETRIC APPARATUS.
---+--------+---------+-------+---------+-------------------------
| | c.c. of | | c.c. of |
| P.D. |N/10 KOH | P.D. |N/10 HCl |
| Before |required After |required |
No.| Skins | for | Skins | for | Description of Liquor
| | 50 c.c. | | 50 c.c. |
| volt |liquor to| volt |liquor to|
| |0·69 volt| |0·69 volt|
---+--------+---------+-------+---------+-------------------------
A1 | 0·622 | 1·95 | .. | .. | New puer
A2 | .. | .. | 0·747 | 1·9 | A1 after 2 packs skins
B1 | ·607 | 3·7 | .. | .. | New puer
B2 | .. | .. | ·770 | 3·1 | B1 after 3 packs skins
C1 | ·580 | 4·3 | .. | .. | New puer
C2 | .. | .. | ·762 | 2·8 | C1 after 2 packs skins
D1 | ·580 | 5·2 | .. | .. | New puer
D2 | .. | 0·8 | ·680 | .. |{D1 after 1 pack skins
| | | | |{(still on the acid side
| | | | |{ of 0·69)
E1 | ·570 | 6·2 | .. | .. | D2 + 4 buckets more puer
E2 | .. | .. | ·720 | 0·8 | E1 after 1 pack skins
F1 | ·610 | 3·0 | .. | .. | New puer
F2 | .. | 0·5 | ·680 | .. |{F1 after 1 pack skins
| | | | |{(still on the acid side
| | | | |{of 0·69)
---+--------+---------+-------+---------+-------------------------
The potential at the neutral point, using an auxiliary electrode
filled with N/1 potassium chloride, was 0·69 volts. Potentials below
this point, therefore, indicate an acid reaction, and, conversely,
potentials above 0·69 volts indicate an alkaline reaction. The
apparatus is thus very useful in following the course of the bating
process. The initial potential also enables the hydrion concentration
of the bate liquor to be determined directly (see Chapter III.).
It was found that during the bating of a pack of skins the hydrion
concentration of the liquor diminished from 10^{-5·2} to 10^{-7·4}
normal.
Such acidities as are found by this method, e.g. 7–8 c.c. N/10 acid per
100 c.c., are too great if made up by taking a solution of the free
acids. The ionization must be almost entirely repressed by the presence
of sufficient neutral salts of the same acids in the bating liquid, in
order to obtain a similar result to the puer.
The table opposite gives the values found for a series of puer liquors,
made with dog manure from hunting-kennels.
The reaction of puer liquors (expressed in c.c. of N/1 alkali or acid
per 1000 c.c. of bate), in a series in which the washed goods were run
for one hour in old puer, out of which goods had been taken, and then
transferred to a freshly-made puer, was as follows:--
----------+----------------+--------------
Bate | Before Goods | After Goods
----------+----------------+--------------
Old puer | Neutral | 28 c.c. acid
Fresh | 10 c.c. alkali | Neutral
Old puer | Neutral | 40 c.c. acid
Fresh | 11 c.c. alkali | Neutral
----------+----------------+--------------
These figures were obtained by the ordinary colorimetric method
described on p. 32.
Adding together the alkalinity of the bate run away, and the acidity of
the new bate which is neutralized, the total for 1 and 2 = 38 c.c. N/1
acid, and for 3 and 4, 51 c.c. N/1 acid.
Multiplying by 810 (volume of bate less volume of dry skin), we find
that the skins have neutralized 30·78 and 41·31 litres N/1 acid
respectively. Since one litre of N/1 acid will neutralize 28 grm. of
lime, it follows that the lime removed by the bate was in one case
862 grm., in the other case 1157 grm.
The 500 kilos, of wet washed grains introduced into the paddle contain
approximately 0·5 per cent. of lime CaO, equivalent to 2500 grm.
altogether. As will be seen from the figures given in table, p. 35, the
free acids present in the fresh bate are only capable of neutralizing
10 × 810 c.c. of normal alkali, and this is equivalent to 225 grm. of
CaO, or 9 per cent. of the total lime.[30]
[30] Eitner, Der Gerber, 566, p. 77, states that little or no
neutralization of lime by acids or acid salts takes place in the bate.
In addition to this, a considerable amount of lime is removed from
the skins which is not found afterwards in solution, but which is
precipitated in an insoluble form during the course of the bating
process. In an experiment to determine the amount of this insoluble
lime, the following figures were obtained:--
LIME IN PUER LIQUOR, GRAMS PER LITRE CaO.
Before Skins After Skins
Soluble lime 0·19 0·485
Insoluble lime 0·13 0·485
---- -----
0·32 0·970
It will be noted that the amount of insoluble lime has increased to a
greater extent than the soluble lime, showing that part of the lime
from the skins has been precipitated in an insoluble form. The increase
of lime in the solution is 0·295 grm. per litre of soluble lime, and
0·355 grm. per litre of insoluble lime, a total increase of 0·650 grm.;
that is, the ratio of soluble lime to insoluble lime in the original
puer is 1·46 : 1. In the used puer it is 1 : 1, so that in the above
case more than half the lime removed from the skins (54·5 per cent.)
has been precipitated in an insoluble form, some of it in the form of
calcium phosphate, and the remainder probably in the form of calcium
oxalate. Crystals of calcium oxalate may be seen under the microscope
in the puer residues.
The oxalic acid is produced by bacterial action, as has been shown by
Zopf[31] and Banning[32]; but it is difficult to estimate it in the
bate, and a reliable analytical method of doing so requires devising.
[31] Ber. Deutsch. Botan. Ges. 1900, xviii. 32, J.S.C.I. 1900, 386.
[32] Centr. Bakt. Parasitenk, ii. Abt. viii., 393, etc., J.S.C.I.
1902, 1151.
A further 30 per cent. to 40 per cent. of the lime in the skins is
removed by the chemical action of the complex amines of the organic
acids, and by the mechanical effect of the paddle or drum, so that the
final result is more or less as follows:--
Per cent.
Lime neutralized by free acids 9
Lime dissolved by complex amines 25
Lime precipitated 30
Lime remaining in the skins 36
---
100
The lime remaining in the skins is not in the caustic state, but
principally in the form of neutral salts (see footnote to p. 24).
[Illustration: Fig. 7.]
Some of these neutral salts appear to be absorbed by the skin during
the course of the bating, for, on examining pieces of the same skin at
frequent intervals during the operation, and determining the ash, it
was found that a minimum point for ash content was reached in about ten
minutes, after which the ash actually increased. The results are shown
in the following table, and also graphically by the curves, Fig. 7--in
which A is a “grain” previously washed as free from lime as possible;
B, an unwashed “roan.” The effect of the absorption of inorganic matter
is very noticeable in both cases. A part of the effect only is apparent
since a certain amount of skin substance passed into solution.
VARIATION OF ASH PERCENTAGE DURING PUERING.
-----------------+--------------------------------
-- | Ash, per cent. on Dried Skin
-----------------+----------------+---------------
Time of Puering | Washed Delimed | Limed Roan (B)
in Minutes | Grain (A) |
-----------------+----------------+---------------
0 | 2·88 | 7·03
5 | 2·91 | --
10 | 3·20 | 3·54
15 | 4·80 | --
20 | 4·08 | 4·24
25 | 4·29 | --
30 | 4·85 | 5·19
35 | 4·59 | --
40 | 4·70 | 5·45
45 | 4·60 | --
50 | 4·45 | 5·67
55 | 4·42 | --
60 | -- | 5·00
-----------------+----------------+---------------
The following analyses give the amount of lime in solution before and
after the bating of the skins, in grams per litre of filtered puer
liquor:--
---+-----------------+------------+-----------+---------------
No.| Bate |Before Goods|After Goods|Increase of CaO
---+-----------------+------------+-----------+---------------
1 |Fresh puer | 0·108 | 0·62 | 0·512
2 | " " | 0·34 | 0·72 | 0·38
3 | " " | 0·20 | 0·52 | 0·32
4 | " " | 0·19 | 0·49 | 0·30
5 |Old puer | 0·54 | 0·84 | 0·30
6 |{Old puer, goods}| 0·98 | 1·38 | 0·40
|{not washed. }| | |
7 |{French puer }| 0·308 | 0·548 | 0·24
|{shop. }| | |
---+-----------------+------------+-----------+---------------
The limit of the quantity of lime in solution in a normal puer, in
the form of calcium salts, appears to be about 1 grm. per litre. If
more lime be presented to the liquor, the goods stop coming down. If
now fresh dung be added, they will continue to come down, but the
quantity of lime in solution does not increase; the excess of lime is
precipitated, partly as phosphate and partly as oxalate, in the way
stated above.
The type of reaction by which the lime is dissolved is similar to that
occurring between ammonium chloride and lime, and is expressed by the
formula--
2NH_{4}Cl + Ca(OH)_{2} = CaCl_{2} + 2NH_{3} + 2H_{2}O
and in the case of the calcium carbonate in the skins--
2NH_{4}Cl + CaCO_{3} = CaCl_{2} + (NH_{4})_{2}CO_{3},
so that every molecule of lime neutralized, liberates two molecules of
ammonia.
Jean states that the production of ammonia progresses regularly during
the puering, and that when the free ammonia reaches 0·2 grm. per litre
the bate is unfit for further use. But if the excess of ammonia be
neutralized by the addition of phosphoric acid, which also precipitates
the lime brought in by the skins, the bate may be kept in constant
use for some time. Jean found 0·06 grm. NH_{3} per litre in the puer
as made up for use, and, after one lot of skins had been put through,
0·086 grm. per litre; after two lots of skins, 0·135 grm. per litre. In
ordinary puer wheels, as used at Trent Bridge, we find--
(_a_) (_b_)
Before goods 0·0816 0·0850 grm. NH_{3} per litre
After " 0·0833 0·0799
so that there is little or no difference before and after puering in
this case.
Part of the ammonia formed escapes into the air; a further portion
unites with the acids which are being formed by the action of bacteria
in the bate (see Chapter IV.), and it is also probable that part
combines in some way with the calcium salts in the bate.
The actual reactions taking place are of course much more complicated
than this simple case, because, instead of ammonia and ammonium
chloride, we have a number of complex salts formed by combination
of organic acids with substituted ammonia derivatives, such as
methylamine, ethylamine, etc. The chief of these are ethylamine and
methylamine butyrates, and lactates, and probably propionates,
although I have not been able to separate the latter.[33]
[33] Fitz (Berichte, 1876–1884, see Herfeldt, J.S.C.I. May 31, 1895),
has shown that lactates in dung are decomposed by bacteria, the chief
product being propionic acid.
The reaction with the butyrate is represented by the equation--
2C_{2}H_{5}NH_{2}C_{3}H_{7}COOH + CaO
= 2C_{2}H_{5}NH_{2} + C_{3}H_{7}COO
\
Ca + H_{2}O
/
C_{3}H_{7}COO
by which it will be seen that the amine is set free just in the same
way as ammonia in the equation on p. 40.
In order to ascertain if the action of the amines was the same as that
of salts of ammonia, I prepared the following compounds and tested
their action on skins at 37° C., a control piece of the same skin being
kept in water at the same temperature. The time in each case was one
hour. All the solutions were neutral.
1. Ethylamine lactate: skin swells slightly, not “down” equal to
puer.
2. Ethylamine propionate: skin moderately fallen, not equal to puer.
3. Ethylamine butyrate: about the same as Exp. 1.
4. Trimethylamine butyrate: very similar action to Exp. 3 and to
ammonium butyrate.
The results correspond very closely with those obtained in previous
experiments with various salts of ammonia (see Chapter VI.), and
justify us in assuming that in all essential respects the action is
similar. The free amines enter into fresh combinations with acids
which are produced by bacterial action, and this process goes on until
all the nutrient material is exhausted.
*The Role of Phosphates in the Bate.*--There is no doubt that the
phosphates in the bate play an important part, but exactly in what
manner they act is not yet known. One of the principal effects is the
part they play as “buffers,” in preventing brusque changes of the
hydrion concentration during the bating process. This has been pointed
out by Soerensen in the case of enzyme reactions. The phosphates in
dung are mixtures, which are capable of fixing both acids and bases;
and so the small quantities of these bodies, which are produced by the
splitting up of the organic matter, are taken up or released as the
case may be.
The chemistry of the phosphates is one of the most complicated branches
of inorganic chemistry, and, as a consequence, the determination of
the constitution of the various phosphates in dung is an extremely
difficult matter, and demands a lengthy research. For instance,
besides the salts directly derived from the three phosphoric acids,
HPO_{3}, H_{3}PO_{4} and H_{4}P_{2}O_{7}, phosphates exist which are
probably derived from hypothetical di-, tri-, or meta-phosphoric
acid, _n_HPO_{3}, and a few salts have been isolated, which are
perhaps derived from the hypothetical acids P_{4}O_{7}(OH)_{6} and
P_{10}O_{19}(OH)_{12} (Watt’s Dict., art. “Phosphates”). Including
the double salts, there are more than 16 different calcium salts of
phosphoric acids. The normal lime salt Ca_{3}(PO_{4})_{2} is very
slightly soluble in water, but its solubility is increased by the
presence of various organic substances such as exist in dung, and part
of the soluble phosphates found in the bate are undoubtedly nothing
more than this salt in solution. This fact has been utilized in the
manufacture of the artificial bate Erodin (see Chapter VII.).
The phosphoric acid in the puer is partly precipitated by the lime in
the skins, and hence diminishes during the bating process. In some
cases practically the whole of the phosphoric acid disappears from the
solution.
The following experiment will give an idea of the amount of lime
precipitated as phosphate. A filtered puer liquor was analysed for lime
and phosphoric acid, before and after the skins were passed through.
The results were, in grm. per litre--
Before After
Soluble lime as CaO 0·364 0·540
P_{2}O_{5} 0·424 0·328
Increase of lime, 0·176 grm.; diminution of P_{2}O_{5}, 0·096 grm.
Calculated to calcium phosphate Ca_{3}(PO_{4})_{2}, this amount of
phosphoric acid has combined with 0·114 grm. CaO. Assuming that the
ratio of soluble to insoluble lime is the same as given, p. 36, then
the lime is distributed as follows:--
Grm.
Increase of soluble CaO 0·176
" " insol. CaO 0·210
Lime as Ca_{3}(PO_{4})_{2} 0·114
Hence " " oxalate (?) 0·096
That is, of the lime precipitated, 54 per cent. is phosphate, 46 per
cent. oxalate.
In another puer containing before use 0·383 grm. P_{2}O_{5} per litre,
only traces of phosphates were found in solution _after_ goods had been
puered in the liquor, and in some analyses by Jean (39) the following
figures were obtained:--
GRAMS OF PHOSPHORIC ACID PER LITRE.
Fresh dung after four days’ maceration 0·082
Bate after one pack of skins 0·036
Bate after two packs of skins 0·018
Although these figures are less than those found at Trent Bridge, they
confirm the fact that the soluble phosphates diminish during the bating
process.
The phosphates in solution thus diminish during the bating, and are
found in the insoluble matter which separates out. A small portion of
the lime remaining in the skins is also converted into phosphate by
the action of the bate. In an experiment to determine this, a portion
of the same skin was taken before and after puering. The pieces
were dried, ashed, the ash dissolved in dilute nitric acid, and the
phosphates precipitated by ammonium molybdate. In the skin before
puering no phosphates were present, but in the skin after puering there
was a small amount, though not sufficient to weigh.
The action of ammonium phosphate on the lime in the skin is very small.
A skin was treated with a 0·1 per cent. solution of ammonium phosphate
at 100° F. for one hour. The CaO in the dry skin was estimated, and
found to be--
Per cent.
Before the experiment 1·93
After " " 1·45
A considerable amount of calcium phosphate was found in the skin after
the experiment.
Other chemical compounds existing in the puer, or formed by the
action of bacteria (principally _B. coli commune_, see Chapter IV.),
are indol, skatol and a number of aromatic oxyacids, principally
para-oxyphenyl-propionic acid, a little para-oxyphenylacetic acid and
skatol carbonic acid. In addition, tyrosin, leucin, tryptophan and
mercaptans have been separated.[34]
[34] Rettger, Amer. Jour. of Physiol., viii. p. 284; Koch’s
Jahresbericht, 1903, p. 112.
With these bodies no experiments on skin have been made, so far as I am
aware, except with indol and skatol. Kathreiner found that these had a
slight reducing action on skin, so that one may say they play some part
in the puering.
The action of the bile salts, glycocholate and taurocholate of soda,
also needs investigation. These have an indirect effect in the puer,
as they favour the development of some species of bacteria (chiefly
_coli_) and hinder the growth of others.
Some action has also been ascribed to sulphuretted hydrogen, but in the
puer liquors which I have examined no H_{2}S was found, either before
or after the skins were entered.
It will be seen that the ammonia compounds in the bate are not of
themselves particularly fitted for the purpose of removing lime[35]
from the skins, but owing to bacterial action (which we shall treat of
in Chapter IV.), acids are produced which combine with the ammonia,
and in this way the small quantity of these compounds originally
present is continually being regenerated while the bating is in
progress. Ammonia is set free by the lime in the skins. It is then
neutralized by acids produced by bacteria, and thus acts as a carrier
for the acids, and the bate remains in a nearly neutral condition. As
the lime increases in the liquid the action of the bacteria diminishes,
and finally the alkalinity becomes too great to allow the bacterial or
chemical action to proceed further.
[35] Deliming with acids when carefully done takes out more lime than
the puer, without in any way injuring the skin, but when tanned with
sumac the bellies and axilla are harsh, and of a browner colour than
in a puered skin. Analysis showed no more lime in the brown portions
than in the centre of the skin, where the colour was quite bright and
satisfactory.
It will be noted that the _concentration_ of the active salts in the
bate is extremely small. If the amine compounds be assumed to consist
of ethylamine butyrate or lactate, the concentration of the solution is
approximately 1 grm. per litre; it is important that the concentration
of salts should not greatly exceed this amount. I have found by
experiment with ammonium chloride solutions, that the best reducing
action is provided by a concentration of 0·7 to 1 grm. NH_{4}Cl per
litre; if the concentration be raised to 2 or 3 grm. per litre, the
skins become “leathery” and do not fall properly. The alkalinity must
not be greater than 3–5 c.c. N/10 per 100 c.c. bate, for the bate to
work at its best.
*Solution of Skin Substance during the Puering.*--The determination
of the total skin substance dissolved by the puer is best done by
Kjeldahl’s method before and after the goods.[36]
[36] Vide Procter, L.I.L.B., 1908, p. 64.
The difference in the total nitrogen found multiplied by 5·6 gives the
amount of skin substance dissolved by the bate, assuming the amount of
nitrogen in the dry ash-free skin to be 17·8 per cent. If very great
accuracy be required, a small correction for nitrogen, brought into
solution from the puer itself, is necessary.[37] This correction must
be ascertained for the particular puer used by actual experiment.
[37] In a blank experiment to determine this, 0·0476 grm. N per litre
was found to be brought into solution from the puer.
The following figures give the results in grams per litre obtained in
the puering of sheep grains. 50 c.c. of the filtered puer liquor are
slightly acidified with sulphuric acid, evaporated nearly to dryness
and Kjeldahled in the usual way.
Mean
Total nitrogen before skins {0·2632} 0·2604
{0·2576}
" " after " {0·4928} 0·4844
{0·4760}
Difference -- 0·2240
Equivalent to 1·254 grm. skin substance per litre. This was somewhat
over a kilogram of skin substance for the paddle in question, and equal
to 1 per cent. of the dry ash-free skin.
As to the differentiation of the dissolved skin substance into
albumoses, peptones, monamino acids, diamino acids, ammonia, etc., a
modification of Stiasny’s method[38] for the examination of soaks and
old limes may be used.
[38] Stiasny, On Old Limes. Collegium 1910, p. 181.
The method is based on the fact, discovered by Schiff, that
formaldehyde reacts with amino acids, forming methylen-amino
acids, which are distinctly acid and allow a sharp titration with
phenolphthalein as indicator, while the amino acids themselves react
almost neutral. Soerensen has worked out a method on this basis for the
determination of different amino acids, and for tracing the course of
hydrolysis of albuminous matters.
Instead of using phenolphthalein as an indicator, the electrometric
apparatus of Sand (see p. 76) is employed. 50 c.c. of the filtered puer
liquor are put into a beaker, the hydrogen electrode is immersed in
the liquor, and the potential difference (P.D.) observed; this gives
the hydrogen ion concentration of the solution. 10 c.c. of neutral
formaldehyde solution (40 per cent.) are added, and the P.D. again
observed; it will be found to diminish rapidly, but soon becomes
constant, indicating that the reaction is a quick one.
The increase of acidity, as shown by the lowering of the potential
difference, is due to the acidity developed by the combination of
the formaldehyde with the amino acids forming methylen-amino acids
of appreciable hydrion concentration. The amount of such acids is
estimated by titrating with N/10 caustic soda solution until the P.D.
rises to the same voltage as that originally found. The following
figures were found in an experiment:--
Original Puer The same
Liquor After Goods
π (volts) 0·61 0·69
π after 10 c.c. formalin 0·53 0·54
N (Kjeldahl), grm. per litre 0·3136 0·5936
Increase of N -- 0·2800
N/10 soda for 50 c.c. to
original voltage 7·0 11·6
c.c. increase N/10 soda -- 4·6
∴ 1 c.c. N/10 soda = mg N -- 3·05
A preferable method is to add decinormal acid or alkali to the original
liquor until the P.D. of 0·69 is reached, at which point the liquor
will be neutral to phenolphthalein, and, after adding formaldehyde, to
titrate with N/10 soda until the P.D. of 0·69 is again reached.
The factor which connects the amount of decinormal soda required for
the titration, after the addition of formaldehyde, with the total
nitrogen as determined by Kjeldahl’s method, will afford information as
to the extent of the hydrolysis undergone by the proteid matter, in the
same manner as Stiasny (loc. cit.), has proposed to differentiate the
dissolved proteid matter in lime liquors. As hydrolysis proceeds the
percentage of nitrogen in the molecule increases, being at its maximum
in the ultimate nitrogenous product ammonia; the factor, therefore,
becomes less as hydrolysis becomes more advanced.
For ammonia 1 c.c. N/10 soda = 1·4 mg. N
" hydrolized gelatin[39] = 2·9 "
" Witte peptone completely hydrolized[39] = 3·6 "
" lysin = 2·8 "
" arginin = 5·6 "
" histidin = 4·2 "
[39] Stiasny. Collegium 1910, p. 184.
We may conclude that the skin substance dissolved in the puer liquor is
hydrolized almost as completely as gelatin is by boiling with sulphuric
acid.
I have previously pointed out that dilute acids dissolve a certain
amount of skin substance (see p. 157), and in this connexion, Dr.
Georges Abt has given me the results of some experiments, on the
solubility of skin in various organic acids, which he made in Vienna.
Pieces of skin, weighing 40 grm. in the wet state, were allowed to
remain for one month in N/10 solutions of the acids. The N was then
determined, by Kjeldahl’s method, with the following results, expressed
as per cent. of the wet skin dissolved:--
Per cent.
Acetic acid dissolved 0·645
Lactic " " 2·27
Butyric " " 0·577
Formic " " 1·47
It will be seen that butyric acid dissolved the least amount of skin,
lactic acid dissolving close upon four times as much.
*Scud.*--A certain amount of skin substance comes away in the “scud.”
This is the liquid squeezed out of the skin by the pressure of the
scudding knife after puering.
The liquid has the same composition as the puer liquor out of which the
goods have been taken, and in addition contains large quantities of
pigment granules, wool roots, and some skin substance, which together
constitute the so-called “filth” of the skin. Analysis of a scud from
English sheep grains showed only 0·164 per cent. N, equivalent to about
1 per cent. skin substance (9·15 grm. per litre). Fat, 7·9 grm. per
litre.
Eberle and Krall have recently[40] analysed the fatty matter which
adheres to the men’s knives in scudding lamb skins for gloving work.
They obtained the following results:--
[40] Ueber die Zusammensetzung des beim Beizen von Lammfellen
mit Hundekot abfällenden “festen Schmutzes”: ein Beitrag zur
Beizenfrage.--Coll., 1911, p. 445.
Per cent.
Water 29·7
Fat 42·0
Fatty acids combined with lime 6·6
Albuminous matter soluble in water 3·8
Hair and insoluble albuminous bodies 14·4
Ash (containing 57 per cent. CaO) 3·5
The fat had a--
Melting-point 40–44°
Saponification number about 121
Iodine number 31·6
Hehner value 91·9
Acid value 9·3
Dr. Fahrion found, in a sample of the fat extracted with ether:--
Per cent. Iodine number.
Unsaponifiable 47·6 27·3
Fatty acids (sol. in petrol ether) 39·3 30·2
Oxy acids (sol. in ether) 13·5 13·4
The figures obtained for the fat therefore agree closely with those for
wool fat.
*Action of the Bird-Dung Bate.*--The depleting action of the pigeon-
and hen-dung bate is very similar to that of the puer, or dog-dung
bate; but the bating process with these materials, as we have seen
(p. 18), is carried out at a lower temperature, and is consequently
more prolonged. The principal difference between the two bates appears
to be a chemical one, due to the fact that bird dung contains all the
urinary products which are present only to a small extent in the
dung of mammals. In birds uric acid is the chief stage in nitrogenous
katabolism, the mechanism of its formation being a process of synthesis
in the liver (Halliburton). Urea is also present in considerable
amount, and does not appear to be so easily decomposed as the urea
in animal urine.[41] As we shall show in the next chapter, urea, and
probably also urates, greatly facilitate the permeability of gelatine,
and to this fact may be ascribed the more gradual action of bird-dung
bates. If we attempt to bate hides with dog-dung, the grain of the hide
is found to be attacked and destroyed before the bate has penetrated
to the interior of the hide. On the other hand, a bird-dung bate may
be used at a temperature of 38° to 40° C. for the puering of skins
destined for light leather, but its action is not so favourable as that
of the puers.
[41] Urea is present to the extent of 5 per cent. in samples of
Peruvian guano.
COMPOSITION OF BIRD EXCRETA.
------------------------+---------------+-------+-------+------
| Pigeon | Hen | Duck | Goose
------------------------+---------------+-------+-------+------
Moisture | 58·32 | 56·08 | 60·88 | 46·65 | 77·08
Organic matter† | 28·25 | 19·56 | 19·22 | 36·12 | 13·44
Phosphates | 2·69 | 2·54 | 4·47 | 3·15 | 0·89
Carbonate and sulphate} | 1·75 | 3·08 | 7·85 | 3·01 |}
of calcium } | | | | |} 2·94
Alkaline salts | 1·99 | 0·82 | 1·09 | 0·32 |}
Silica and sand | 7·00 | 17·92 | 6·69 | 10·75 | 5·65
------------------------+-------+-------+-------+-------+------
|100·00 |100·00 |100·00 |100·00 |100·00
------------------------+-------+-------+-------+-------+------
† Containing nitrogen } | | | | |
equal to ammonia } | 1·75 | 1·21 | 0·74 | 0·85 | 0·67
------------------------+-------+-------+-------+-------+------
Macadam[42] states that pigeon dung is the most concentrated. Hen
manure contains the largest proportion of phosphates, and is followed
by duck droppings. That of the goose is the least valuable. The
preceding table is taken from his paper.
[42] Manures, Natural and Artificial, W. Ivison Macadam. Jour. Soc.
Chem. Ind. 1888, p. 79.
Procter[43] quotes the following, as a mean of 40 analyses of pigeon
dung by Schulze:--
[43] Principles of Leather Manufacture, p. 179.
Per cent.
Water 21·00
Nitrogen 2·53
Phosphoric acid 1·79
Potash 1·46
He remarks that the action of bird dung is more penetrating, but less
softening and loosening than that of dog dung, and this effect may be
explained by what has been said above.
Unfortunately, far less work has been done on the bird-dung bate than
on the puer, and there is a wide field open for research in this
direction.
CHAPTER III.
THE PHYSICS OF BATING.
“The most important aspect of any phenomenon, from a mathematical
point of view, is that of a measurable quantity.” --MAXWELL.
It is impossible in the space of a short chapter to give an adequate
explanation of the physical changes taking place during the puering
process. An outline only can be given, and perhaps a few signposts to
indicate for those interested, in what direction further work can be
usefully done. It is obvious that if more be attempted, a treatise on
physics and physical chemistry would be required; such a work is beyond
the scope of the present volume. It is to be hoped that the whole of
the questions dealt with here, including the physical chemistry of skin
and of the whole tanning process, will shortly be fully treated by the
master hand of our greatest tanning chemist, Professor H. R. Procter.
Since tanning, in the earlier stages, is for the greater part a
physical absorption, or colloidal co-precipitating action,[44] the
physical state of the skin fibre, or condition of the skin before it
enters the tanning liquor, is of the greatest importance. In fact,
the whole of the operations to which the skin is subjected previous
to tanning are directed towards changing its physical state, and the
chemical changes undergone are small and principally hydrolytic.
[44] Stiasny, Kritische und Experimentelle Beiträge zur Aufklärung
der Gerbvorgänge. Collegium 1908, p. 117.
Wood, Compounds of Gelatin and Tannin. Collegium 1908, p. 494.
The two most important physical influences over which we have control
are pressure and temperature.
The pressure during puering is practically constant, viz. the
atmospheric pressure, but, as we shall see later, a diminution of
pressure is favourable to falling or depletion. It would, therefore,
be interesting to conduct experiments on puering in vacuo, or under
reduced pressure.
Before considering the effect of temperature and the changes in the
volume of the skin during puering, it will be well to consider the
properties of the skin and the puer liquor.
In the skin prepared for tanning, practically all the keratin and
epidermis and soluble matters are got rid of, and we have a mass of
fibres which are composed of collagen, a proteoïd, which by prolonged
boiling with water is converted into gelatin.
Neither the chemical formula nor the molecular weight of collagen is
known with certainty, but, from a series of ultimate analyses, the
change of collagen into gelatin is represented by Hofmeister[45] by the
following equations:--
[45] Allen, Comm. Org. Analysis, iv. p. 459.
C_{102}H_{149}N_{31}O_{38} + H_{2}O = C_{102}H_{151}N_{31}O_{39}
collagen gelatin
from which it will be seen that he assigns a molecular weight of 2416
to collagen, and 2434 to gelatin. Other considerations, however, make
it probable that the molecular weight is double the above figures.
Gelatin is a typical colloid, and we may consider that skin is
practically a colloid with a structure (a very important point, as
we shall see later), but behaving in many ways as gelatin. The puer
solution is to a large extent colloidal. Therefore, both the skin
and the puer are in the colloidal state. In the typical crystalloid
solution of an electrolyte, the dissolved body is separated into its
molecules, and to a large extent into individual ions, while, in the
colloid state, the units of distribution are either large and often
conjugated molecules, or more frequently minute particles composed
of many molecules united by cohesive attraction.[46] In the case of
the skin the molecules are not free to move, but are held in place by
the structure of the skin, and the fibres thus act as semi-permeable
membranes, with capillary spaces between them, in which water and other
fluids are merely held by capillary attraction.
[46] Procter, Colloidal Chemistry. Brit. Assoc. Rep. 1908.
If filtered puer liquor is put into a vessel closed by a membrane of
skin, and the whole immersed in clear lime water, the puer solution
becomes turbid in a short time, but the outer solution remains clear,
showing that the skin is permeable to the lime solution (crystalloid),
but not to the puer solution (colloid). It was observed, however,
that the acids contained in the puer diffused through the membrane;
this was shown by the addition of a few drops of phenolphthalein to
the lime solution, when the pink colour disappeared after a short
time in the neighbourhood of the skin. These phenomena are due to
osmosis. It is the fundamental property of all animal membranes, to
allow some substances to pass through them more easily than others.
In many cases, such membranes, while freely permeable to water, are
practically impermeable to certain substances in solution, and play
the part of sieves in directing and controlling the diffusion. In the
case of skin the phenomena are complicated by the fact that the skin
combines chemically with many substances in solution, and thus we do
not always know what part to assign to chemical combination and what to
the osmotic phenomena.
Procter has shown (Colloid. chem. Beihefte 1911, ii., pp. 243–284)
that, while gelatin is very permeable as such to solutions of acids
and salts, there may be formed in the presence of excess of acid a
hydrolysable chemical complex of the nature of a salt, in which the
gelatin functions as base, and which is probably less permeable to
acids and their salts than the neutral gelatin. The conditions would
then be similar to those which obtain when solutions of an acid and
its salt are separated by a movable membrane, which is permeable for
the acid and water but not for the salt solution. From the organized
structure of the skin surface, it is unlikely that osmosis takes
place between the skin itself and the outer solution, with the two
surfaces of the skin as semi-permeable membrane. Osmotic action is most
likely to occur in the interior of the skin, between the skin fibres
themselves and the interfibrillar spaces. The colloids in the puer
solution, which constitute a large proportion of its material, cannot,
from their nature, penetrate the skin. This may be shown by the
above-mentioned experiment. From this it is reasonable to assume that
the lime is not actually dissolved from the interior of the skin by the
puer acids, but that solution takes place for the most part after it
has diffused out into the puer solution. It is probable, however, that
part of the bodies of acidic character present in the puer are capable
of penetrating the skin fibre, as has been explained above.
The intensity of the osmotic action of puer upon skin must depend upon
the quantity of substances contained in it, to which skin substance
acts as an impermeable membrane, and which on that account induces an
osmotic pressure between the outer puer solution and the solutions
held in the skin fibre. The effect of puering does not necessarily
imply the actual expulsion of water from the skin--in fact, well puered
skin may quite possibly contain as much water as it did in the swelled
condition. The difference consists in the manner in which the water
is held in the skin, and its freedom to move from parts which are
submitted to pressure. In the swollen skin, the fibres may be conceived
as swollen by the water and holding it in the same manner as a gelatin
jelly; after puering, the fibres are “fallen,” and the water, hitherto
held by them, surrounds them in the liquid form.
The osmotic pressure[47] of a solution of concentration _c_,
temperature T, and pressure _p_, is the difference of pressure
exerted on both sides of a semi-permeable membrane in thermodynamic
equilibrium, having on the one side the solution under the above
condition, and on the other side the pure solvent under the pressure
_p__{0} of its own saturated vapour. On this definition the osmotic
pressure of a normal solution is over 22 atmospheres, or 330 lb. per
sq. in.; and since a saturated lime solution is about 1/20 normal,
its osmotic pressure is about 1·1 atmospheres, or 16 lb. per sq.
in.--this represents the force causing the lime to diffuse into water
in which the skin is placed. The puer solution being of a colloidal
nature, exerts practically no osmotic pressure, and since it contains
substances capable of entering into combination with lime, the latter
is removed from the surface very quickly. The curve representing the
removal of lime by water has been given in Chapter I., p. 6. That for
puer is not of such a simple character (see Fig. 7, p. 38), but it
will be seen that the greater part of the lime is removed during the
first 10 minutes. The curve is plotted for percentage of ash, since
the lime is no longer in a caustic condition but in the form of salts.
It is remarkable that the percentage of ash, after reaching a minimum,
_increases_ considerably. This phenomenon still requires investigation.
[47] M. Planck, Zeit. f. Phys. Chem. xlii. p. 584 (1903).
*Density of Skin.*--Coming to the consideration of the volume of skin
and its changes during puering, we know that the volume _v_ is the
reciprocal of the density, i.e.--
_v_ = 1/δ,
and therefore
δ = 1/_v_.
Carini[48] has carried out exhaustive experiments on the density of
skin during tanning, but, so far as I am aware, little or no work has
been done as to the effect of puering on the density of raw skin.
[48] Sull’ appliccazione della bilancia idrostatica per il controllo
della concia delle pelli, Milan, 1903.
The usual methods of determining density are well known,[49] and
consist in weighing the body first in air, then in water or other
liquid. If _m_ be the weight of the body, and it loses the weight _w_
when weighed in water--
δ = _m_/_w_.
[49] _See_ Kohlrausch, An Introduction to Physical Measurements,
1894, p. 43. _See also_, Weighing Hides in Water, C. E. Parker and
G. H. Russell, Tanners’ Year-Book 1905, p. 45.
For experiments on skin, instead of weighing in water it has been found
more convenient to use a simple volumenometer, which was devised by Mr.
Douglas J. Law (see Coll. 1911, p. 230.)
[Illustration: Fig. 8.--Volumenometer for Raw Skin.]
The apparatus (Fig. 8) consists of the two vessels A and B, connected
by means of thick rubber tubing to the burette C, of which the top is
enlarged to a bulb. The bottle A, which was specially made for us by
Messrs. Townson and Mercer, London, is of about 1 litre capacity, and
the wide mouth is closed by a stopper, accurately ground to fit the
neck, and extending down to the bottom of the neck. The upper part
of the stopper is elongated to a tube, which is closed by the tap G.
The vessel A is also fitted with a tap E. The vessel B serves as a
reservoir, and is used to adjust the level of the liquid in the burette
C by means of the tap at F. To find the volume of a piece of skin, the
method of procedure is as follows. The bottle A is filled with water
up to the neck, and the stopper D, carefully greased, is inserted.
The tap E is then closed, and the burette is filled with water. Then,
with the taps G and E open, the bottle A is filled with water up to D
by raising the burette. G and E are then closed, and by opening the
tap F the level of the water in the burette is adjusted to zero when F
is again closed. G and E are then opened again, and, by lowering the
burette, the water in A is allowed to fall below the level of the neck
of the bottle. E is then shut, the stopper D removed, and the piece
of skin is carefully introduced, avoiding air bubbles. The stopper
D is then replaced with the tap open, and, by opening E and raising
the burette, the water is allowed to come up to the stopper D again.
The taps G and E are then closed, and the volume of the piece of skin
read off directly from the burette scale. Volumes up to 50 c.c. are
measurable as described above, but larger volumes may be measured if a
known volume of water is run from the burette into the reservoir before
introducing the skin.
By using various solutions in the apparatus instead of pure water,
the real swelling or contracting effect of these upon the skin may be
observed. The skin is introduced into the bottle A, and the solution
adjusted to G, which is then closed; then, by leaving the tap E open,
the real swelling or contraction of the skin is measured by the rise or
fall of the liquid in the burette.
Petroleum or other liquid may be used instead of water; in some cases,
the use of petroleum is more advantageous.
The density of dry gelatin as determined by Lüdeking is 1·412, which
is not greatly different from that of skin. Carini gives the following
figures for ox-hide:--
Skin with hair 1·450
" depilated with lime 1·425
" depilated with sodium sulphide 1·441
but does not give details how these figures were obtained, and if
corrected for ash and fat.
The density of limed and puered sheepskin, determined by drying
the skin over sulphuric acid until the weight was constant, then
determining the volume in petroleum, gave the following results:--
Limed skin 1·2335
Puered " 1·2590 I.
By determining the volume of the wet skin in the volumenometer, and the
per cent. of water on drying the skin, the calculated densities were--
Limed skin 1·438
Puered " 1·300 II.
Correcting for ash and fat, the dry ash-free skins had the densities--
Limed skin 1·397
Puered " 1·335 III.
The density of the wet limed skin was 1·063, but the density calculated
from the results (I.) above is 1·0475; from this, it is evident the
fibres of the swollen limed skin undergo compression on swelling, or
that the water contained in them is in a state of compression, in the
same way as gelatin swollen with water occupies a less volume than the
sum of the volumes of gelatin and water. Lüdeking[50] found for 10 per
cent. gelatin jelly δ = 1·069; δ calculated was 1·041. He attributed
the whole of the compression to the water, so that 1 c.c. of water in a
10 per cent. gelatin jelly occupied a volume of 0·96069 c.c. See also
par. 4 p. 68.
[50] Wiedemann’s Annal d. Physik, xxxv. p. 352 (1888).
It may be of interest to give the figures used in the preceding lines
in tabular form.
---------------------------------------+----------+------------
|Limed skin|Puered skin
---------------------------------------+----------+------------
Density of wet skin | 1·063 | 1·053
Per cent. of water found | 80·63 | 78·2
" " calculated | 79·50 | 79·9
" of ash on wet skin | 1·71 | 1·17
" of fat " " | 0·151 | 2·6
Density of dry ash-free skin substance | 1·3970 | 1·3356
---------------------------------------+----------+------------
In addition to the diminution of the density of the skin by puering,
the increase of fat is very marked.
The percentage of water referred to the wet skin may be calculated from
the formula
((_v__{2} - _v__{1})/(1 - _v__{1})) x 100
where _v__{1} = specific volume of the dry skin.
_v__{2} = specific volume of the wet skin.
The specific volume of the dry skin (_v__{1}) may be calculated from
the specific volume of the wet skin (_v__{2}), the percentage of water
(_w_) being known by the following formula:--
_v__{1} = (_v__{2} - (_w_/100))/(1 - (_w_/100)),
and by comparing the volume thus obtained with the volume determined by
direct experiment, the amount of contraction is ascertained. In the
case we have been considering (viz. limed skin with 80 per cent. water)
_v__{2} calculated = 0·955
_v__{2} found = 0·941
The specific volume of the dry skin
_v__{1} calculated = 0·6955
_v__{1} found = 0·8112
The difference for the dry skin is surprising, and considerably
greater than anticipated, but has been verified by a large number of
experiments. It may be remarked that the exact determination of the
density of skin by drying out pieces is liable to error on account of
the non-homogeneity of the pieces. There appears to be some chemical
combination between the water and the skin very similar to that
between water and alcohol, and although the figures obtained in the
above experiments by this method are accurate, it is not certain that
they represent the true density. It is possible that the interior of
the skin may still contain some moisture, and, in order to arrive at
absolute certainty, it would be necessary to powder the skin, and
ascertain its density in a finely divided condition.
When this is done, the results obtained are very much more concordant
than when pieces of skin are used. The following results were obtained
for the density of dry hide powder (as used for analysis by the
I.A.L.T.C.):--
In petroleum ether 1·2568
In carbon tetrachloride 1·2570
In alcohol 1·2580
Mean 1·2572
This is equivalent to a specific volume _v__{1} = 0·7954.
The density of the powdered skin may also be determined in the air
volumenometer (Say; Kopp. Kohlrausch Physical Measurements, p. 53).
*Swelling and Falling.*--The skin, in its living condition on the
healthy animal, is the most supple and perfect of coverings, and in
producing soft leathers it is the object of the tanner to retain this
supple condition. To do this, the swollen fibres must, as we have
seen, be got back to their natural state. The phenomena of swelling
and depletion of skin have been discussed by Körner,[51] and recently
Prof. H. R. Procter[52] has published a paper which goes into the whole
theory of colloidal swelling. In order to understand depletion, which
is the opposite of swelling, it is necessary to consider what takes
place when a body like skin is swollen. I am indebted to Dr. Th. Körner
for the following summary of the phenomena of swelling. There are three
types of swelling: 1. Capillary attraction; 2. Endosmose; 3. Molecular
imbibition.
[51] Th. Körner, 10 Jahres. Bericht, d. Deutsch. Gerberschule zu
Freiberg, 1899, p. 32.
[52] Procter, Ueber die Einwirkung Verdünnter Sauren und Salzlösungen
auf Gelatine, Kolloid Chem. Beihefte, 1911, ii. p. 243.
The last named is of the greatest importance in tanning. Körner (loc.
cit.) enumerates certain principles governing molecular swelling.
1. A body capable of swelling, when put into water, absorbs a
_definite_ quantity of the water up to a maximum, which cannot be
exceeded. (C. Ludwig.)
2. The maximum of swelling depends upon the chemical composition of
the body, on its cohesion and elasticity, and on the temperature and
interior pressure of the liquid. (C. Ludwig.)
3. Power of resistance to swelling increases from the exterior to the
interior, according to a parabolic law; i.e. the external layers of the
body attain the maximum swelling sooner than the internal portions. (L.
Mathiessen and A. Schwarz.)
4. The volume of the swollen body is smaller than its original volume,
plus that of the liquid absorbed. (Quincke.)
5. Swelling is accompanied by development of heat.[53]
[53] Duvernoy, E. Wiedemann, and Lüdeking, Wied. Ann. xxv. 1885, p.
145.
The production of heat is simply due to the contraction, and not to any
chemical phenomenon, such as hydration.[54] This explains a fact well
known to tanners, viz. that skins swell in cold water and “fall” in
warm water. Riecke[55] concludes that the degree of swelling, _m__{2}/M
(where _m__{2} = mass of water absorbed, M = mass of the body swollen),
in a space filled with aqueous vapour, unsaturated, is a function of
the pressure and temperature.
[54] Rodewald. Thermodynamik der Quellung, Zeit. f. Phys. Chem. xxiv.
1897, p. 193.
[55] Zur Lehre von d. Quellung, Wied. Ann. liii. 1894, p. 564.
The velocity of swelling (Pascheles) may be expressed by the formula--
_d_Q/_dt_ = (M - Q)K
where M = maximum of swelling, Q = amount of swelling in the time _t_,
and K = a constant.
The differential quotient _d_Q/_dt_ gives the velocity for each moment,
and it will be seen that the swelling becomes slower and slower as the
maximum is approached. Thus, the law of the velocity of swelling is
identical with that of the velocity of inversion of cane sugar, itself
an application of the law of masses.[56]
[56] Nernst and Schönfliess. Einleitung in die mathematische
Behandlung der Naturwissenschaft, München 2 Aufl. 67.
For every process of swelling, the constant K must be determined
experimentally from observation of M, and it may be shown that--
K = 1/_t_ log(M/(M - Q))
whence the value of K may be calculated for each series of
determinations.
On the manner in which water is held in swollen colloid bodies, three
hypotheses have been put forward.[57]
[57] See also Colloidal Chemistry, H. R. Procter, M.Sc., Brit. Assoc.
Reports, Dublin, 1908.
1. The hypothesis that colloids have a structure in the form of a
honeycomb. (Bütschli.)
2. The water is absorbed at the surface of colloids in a specially
condensed form.[58]
[58] Wilhemy. Pogg. Ann. cxix. pp. 121, 122.
The water forms, with the swollen body, a “solid solution.” (Nägeli.)
Swelling, and its opposite, contraction, are connected with the surface
tension between the swelling or contracting bodies and the surrounding
solution. With diminished surface tension, the surfaces of contact
between the two become greater, i.e. swelling takes place, with
simultaneous diminution of the volume of the whole system, and vice
versa.
For the absorption phenomena which occur, the following relation holds
good: When a substance in solution diminishes the surface tension at
the dividing surface, its concentration is increased; it is absorbed.
When a substance in solution increases the surface tension at the
dividing surface, its concentration is diminished.
In the system water-hide substance the researches of Wiedemann and
Lüdkeing have shown that swelling is accompanied by evolution of
heat. Since a rise of temperature is favourable to a system formed by
absorption of heat, it therefore hinders swelling and vice versa. This
is confirmed by practical experience, and most bating operations are
conducted at temperatures between 35° and 40° C.
With regard to the influence of pressure on swelling, a similar law
holds good as for temperature, which may be expressed as follows.
When a chemical system is compressed at constant temperature, its
equilibrium is shifted in that direction by which the reaction is
accompanied by diminution of volume. Quincke, however, has shown
what appears to be a paradox, namely, that swelling is accompanied
by diminution of volume, i.e. the swelling substance, plus the water
taken up, occupies a smaller space than the sum of the two constituents
taken together; therefore, an increase of pressure must be favourable
to swelling, and conversely a diminution of pressure is favourable to
“falling.”
We must clearly bear in mind that in all cases of swelling, it is the
entry of water into the system which is the cause of the swelling, and
since puering is a process which acts in a contrary direction, i.e. the
skin falls, this means that water is expelled from the system, skin
plus water. By direct determination, from 3 to 8 per cent. of water is
expelled during puering. Calculations made from density determinations
are masked by the fact, above referred to, that the density of the skin
changes during puering.
A fallen skin contains less water than when in the swollen condition,
but the difference between the percentages of water in the skin in the
two states is only relatively small, and obviously insufficient in
itself to account for the great difference in the physical properties
of the skin in the two conditions. It is evident, therefore, that
the state in which the water is held in the two stages must be
different. It is reasonable to suppose that, in the case of swollen
skin substance, the whole of the capillary cavities of the organized
structure of the skin are completely filled with water, which, owing to
its incompressible nature, confers upon the skin elastic and unyielding
properties which it always possesses in this condition. The water,
entering the organized cell structure in the first place by osmotic
pressure, is fixed there and confers upon the skin, in part, its own
property of incompressibility. It is a well-recognized fact that,
during the puering process, large quantities of the skin substance are
dissolved by the action of the enzymes in the bate, and it is probable
that the finer organized structure is first attacked. The walls of the
cells which hold the water are partly destroyed, leaving the skin with,
quite possibly, the same amount of water contained in it as a whole,
but with the water dispersed at large throughout its interior structure
instead of being held in the fibres. The result of this is, that when a
small area of the puered skin is subjected to local pressure the water
in the portion undergoing compression is free to move into the adjacent
portions of the skin, and there is no force acting upon it, except that
of capillarity, to cause it to return to that area when the pressure
is removed from it. When a portion of a puered skin is compressed,
the surrounding part is always swollen to an equivalent amount. That
this view is, in the main, correct is supported by an observation of
Abt (Paris), that, while cell nuclei may be demonstrated in the layers
near the epidermis of an unpuered skin, they are entirely absent from a
puered skin, showing that the puer has completely dissolved the nuclear
structure of the cells.
The swelling caused by alkalis is of a different nature to the swelling
caused by acids. Procter has pointed out[59] that alkaline swelling is
not repressed by sodium chloride, even when caused by sodium hydrate,
but is repressed by sufficient concentration of the hydroxyl ion in the
outer solution.
[59] Colloidal Chemistry, p. 19.
Müller[60] points out that jellies containing certain non-electrolytes
(glucose, glycerine, alcohol) render the diffusion of soluble matter
much slower than pure jellies of the same concentration, but the
presence of urea favours the permeability of gelatin and agar jellies.
The differences in the velocity of diffusion of various salt solutions
through jellies of the same strength, are thus not due altogether to
the greater diffusibility of the particular salt solution, but are to
be attributed to the influence of the salt on the permeability of the
colloidal medium. Limed skin treated with a 1 per cent. solution of
urea at 43° C. is depleted or “falls,” but both the solution and the
skin remain alkaline.
[60] Allgemeine Chem. d. Kolloide, p. 13.
Přibram[61] has recently shown that the swelling and contraction of
muscle are to be ascribed to absorption and expulsion of water from
the cells of the muscle; the rapid changes taking place, are brought
about by changes in the concentration and composition of the liquid
components of the muscle. Lactic and phosphoric acids are produced with
enormous rapidity, and of relatively high concentration; during a short
period these cause instantaneous changes in the swelling of the muscle
cells, followed by a return to their original state. For the evidence
of this the original paper must be consulted, but it goes to show that
the equilibrium of the system--colloids, electrolytes, water--depends
on the proportions and quantities of each of these constituents. The
phenomena we are considering thus conform to the general law of mass
action (Guldberg and Waage).
[61] Přibram, Die Bedeutung der Quellung und Entquellung für
physiologische und pathologische Erscheinungen. Kolloid Chem.
Beihefte, ii. p. 1.
*Influence of Solid Matter in the Bate.*--It was first pointed out by
Wood (J.S.C.I. 1899, p. 991) that a filtered puer liquor had less
action on the skin than an unfiltered liquor containing much finely
suspended matter.
On adding an inert solid (kaolin) to the filtered bate, the action was
hastened. No doubt much of the colloidal matter, and with it some of
the enzymes, are removed by filtration, but nevertheless, the suspended
particles in the bate have some effect on the process.
In a most interesting paper, Perrin[62] has recently shown, that
the granules in suspension in a colloidal liquid function like the
invisible molecules of a perfect gas with a molecular weight of 3·3
x 10^{-9}. Such granules are endowed with the molecular (Brownian)
movement, and therefore may exert a mechanical effect on the fibres
of the skin. Although the mass of the particles is large[63] compared
with molecular dimensions, they are small enough to penetrate the
pores of the skin, and where puering is carried too far, may become
deposited beneath the fine hyaline layer, and thus render it cloudy and
unsuitable for fine colours.
[62] Perrin, Kolloid Chem. Beihefte, i. p. 221.
[63] A particle of gamboge in a colloidal solution has a mass 10^9
times that of a molecule of hydrogen.
*Hydrogen ion Concentration of Puer Liquors.*--It has already been
shown, in Chapter II., that fresh puer liquors have a certain acidity
(7 c.c. N/10 per 100 c.c.) at the commencement of the operation, but
that at the end they are alkaline (3 c.c. N/10 per 100 c.c.). If an
artificially acid liquor be made by diluting hydrochloric acid until it
shows the same number of c.c. by titration, it will be found far too
“strong,” and will swell the skins. This brings us to the consideration
of what is meant by the strength of acids.
Procter and Jones[64] have drawn attention to the point in their paper
on “Acids in Tan Liquors.” As is well known, the ionic theory affirms
that degree of acidity depends on the concentration of hydrogen ions, a
strongly acid solution being one in which the hydrion concentration is
great, an alkaline solution one in which it is extraordinarily minute,
and if we adopt pure water as our standard of neutrality, a neutral
solution is one in which the hydrion concentration is approximately
10^{-7} normal. A normal solution of hydrogen ions would contain 1 gram
of hydrogen ions per litre; in the case of hydrochloric acid this would
equal 1·35 N/1 HCl.
[64] Acids in Tan Liquors, Journ. Soc. of Chem. Ind., 1910, p. 1354.
Sand and Law,[65] and Wood, Sand and Law,[66] have described the mode
of estimating the hydrogen ion concentration in tan liquors directly
by means of the electrometric method, and this method is especially
applicable to the estimation of the hydrogen ion concentration in
puer liquors. It can also be used to titrate the liquors, and we have
already given some of the results in Chapter II.
[65] Journ. Soc. Chem. Ind., 1911, p. 3.
[66] Ibid., 1911, p. 872.
The method is based on the theory of Nernst, that the difference of
potential between a metal plate and the solution of one of its salts
into which the metal is dipping, depends on the osmotic pressure of
the free ions of that metal in the solution (in other words, on the
concentration of the solution). In the case of hydrogen ions, we use
a plate of platinum coated with platinum black and saturated with
hydrogen, and the difference of potential depends, therefore, on the
concentration of the hydrogen ions in solution.
[Illustration: Fig. 9.--Diagram of Connexions of Electrometric
Apparatus.]
The accompanying figure (Fig. 9) shows the hydrogen electrode I, and
the auxiliary electrode II, drawn to scale,[67] on the right, whereas
the electrical apparatus is explained diagrammatically on the left.
[67] An improved form of hydrogen electrode devised by Dr. H. Sand
may now be obtained from Universitäts-mecanikes Fritz Köhler,
Leipzig. It is shown at I in Fig. 10.
The principle of the method of measurement consists in connecting the
two ends P and Q, of a sliding rheostat to the terminals of a dry cell,
D, and balancing the potential-difference to be measured against the
potential-difference between one end, P, and the slider, S, by means
of a special form of enclosed capillary electrometer, E. The value of
this potential-difference is read directly on a delicate voltmeter, V.
The connexions, which are found ready-made in the box, have been drawn
out, whereas, those to be made by the operator are shown by dotted
lines. The steps to be taken by the latter, consist first in taking off
the capillary electrometer and manipulating it in such a manner, that
on returning it into position the capillary may be partly filled with
a thread of mercury and partly with the acid. The terminals, X and Y,
marked battery + and −, are connected to a dry cell, and the terminals,
Z and U, marked cathode and auxiliary respectively, to the hydrogen and
calomel electrode. Very careful insulation of the connexion between the
terminal marked auxiliary and the calomel electrode is necessary. The
hydrogen is passed through the hydrogen electrode until a constant P.D.
between it and the calomel electrode is obtained. This P.D. is measured
by moving the slider up and down until no movement of the mercury in
the capillary electrometer is observed on depressing the key K marked
electrometer.
Fig. 10 is a view of the apparatus as set up for the titration of
a puer liquor. H is a cylinder of compressed hydrogen;[68] I, the
hydrogen electrode, dipping into the beaker C containing the liquor for
titration; _b_, the burette, containing N/10 acid or alkali; II, the
auxiliary electrode, the capillary of which is also seen dipping into
the beaker C; P, the potentiometer box containing the sliding rheostat
S and electrometer E; D, a dry battery. The acid or alkali is run in
from the burette until the voltmeter shows 0·69 volts, indicating that
the liquid is neutral or has a hydrogen ion concentration of 10^{-7}.
[68] It is necessary to use pure hydrogen. This may now be obtained
commercially from the Knowles’ Oxygen Co., Wolverhampton.
[Illustration: Fig. 10.--Electrometric Apparatus.]
The following table shows some results obtained on puer liquors before
and after skins have been put through. _p__{H+} has been called by
Sorensen the exponent of the hydrogen ion concentration C, and is
defined by the equation
_p__{H+} = log(1/C)
i.e. it is equivalent to the logarithm of the reciprocal of the factor
of normality of the solution with respect to the hydrogen ions.[69]
_p__{H+} for pure water or a neutral solution is 7, corresponding
to 0·69 volts. The measurements were made on filtered puer liquors,
using a N/1 KCl calomel electrode as auxiliary, the capillary of the
electrode being filled with 3·5N potassium chloride:--
[69] The formula for calculating _p__{H+} for the N/1 auxiliary
electrode used is as follows:--
Since π = (0·283 + 0·0575 log(1/C) volt)
log(1/C) = _p__{H+} = (π - 0·283)/0·0575
π = potential difference found
C = concentration of hydrogen-ions.
---+------------------+--------+---------
| Before goods. | After goods.
+--------+---------+--------+---------
No.| Volts. | _p__{H+}| Volts. | _p__{H+}
---+--------+---------+--------+---------
1 | 0·560 | 4·7 | 0·755 | 8·16
2 | 0·585 | 5·16 | -- | --
3 | 0·600 | 5·4 | 0·658 | 6·44
4 | 0·595 | 5·35 | 0·710 | 7·35
5 | 0·600 | 5·4 | 0·725 | 7·6
6 | -- | -- | 0·770 | 8·35
---+--------+---------+--------+---------
No. 6 was a very old “spent” liquor. The mean hydrogen ion
concentration before goods was 0·588 volt, i.e. the concentration
was 10^{-5·32} normal equivalent to 0·00000479 grm. per litre of
hydrogen ions. Therefore the value of _p__{H+} was 5·32. A solution of
hydrochloric acid of the same strength by titration consumed 0·7 c.c.
N/1 alkali per 100 c.c. Measured by the electrometric apparatus, it
showed 0·410 volt, corresponding to _p__{H+} = 2·1, or a hydrion
concentration of ·0079N. In other words, the HCl solution has an
acidity or strength 1600 times that of the puer liquor.
The mean hydrogen ion concentration of the liquors after goods was
0·000000076 grm. per litre, corresponding to 0·715 volt and _p__{H+} =
7·12, i.e. the liquor was alkaline to a slight extent. For comparison
saturated lime-water gave a reading of 1·01 volt, corresponding to
_p__{H+} = 12·5.
The hydrogen ion concentration is of the greatest importance for the
proper action of the enzymes in the bate;[70] we shall, however, treat
of this in Chapter VII.
[70] _Vide_ Sœrensen, Sur la mesure et l’importance de la
concentration des ions hydrogène dans les réactions enzymatiques.
Comp. rend. Lab. de Carlsberg, 8me. vol. 1^{ere} livraison,
Copenhagen, 1909.
*Conductivity of Puer Liquors.*--It was thought of interest to examine
the electrical conductivity of puer liquors in actual use, in the hope
that the numbers obtained might give some useful indications. It was
found that the conductivity increased, as might be expected from the
lime going into solution, but the difficulties of the method render it
of less use than ordinary chemical analysis. The results of a typical
liquor are given here as a record--
Conductivity (K) of liquor before goods
0·00316(1/(ohm × cm.))
Conductivity (K) of liquor after goods
0·00423(1/(ohm × cm.))
The difficulty of expressing the complex reactions of puering
numerically is, we have seen, very great, for, as Minot[71] says, “with
human minds constituted as they actually are, we cannot anticipate that
there will ever be a mathematical expression for any organ or even a
simple cell, although formulæ will continue to be useful for dealing
now and then with isolated details. Nevertheless, the value of graphic
methods to every student of science has been immense.”
[71] Minot, Address to Amer. Assoc. for Advancement of Science,
Minneapolis, Dec. 29, 1910. Nature, 1911, p. 96.
It has long been my endeavour to express quantitatively the degree to
which a skin has fallen. My friend Dr. Sand has suggested that this may
be done by subjecting a piece of the skin successively to increasing
and then decreasing pressures, and measuring the thickness under each
load. Experiments carried out with the apparatus described below show
that a limed skin treated in this way is first compressed, and then on
releasing the pressure recovers more or less of its former thickness,
according to the amount of plumping it has received, i.e. it shows a
certain amount of resilience. A well-puered sheep-skin, on the other
hand, shows no resilience at all, i.e. on releasing the pressure the
whole of the compression persists. In the case of an ox-hide subjected
to a bate of hen-dung, a slight recovery takes place on releasing the
pressure. This accords with the fact that it will never be possible
to puer a thick ox-hide so effectively as a thin sheep-skin. A piece
of india-rubber, on the other hand, is completely resilient, i.e. it
wholly recovers its thickness on releasing the pressure. The relative
thickness of the same skin in the limed and puered conditions under
varying loads is also of interest. The process of puering may, as
a rule, be taken to reduce a limed skin to between two-thirds and
one-half of its thickness in the swollen condition. If both limed and
puered skin be then subjected to the same load, the puered skin will at
first be compressed very much more than the limed one. This is probably
due to the expulsion from it of water, held simply by capillary
attraction. On further increasing the load, however, the compression
decreases greatly in the case of the puered skin; with both limed and
puered skin increase of compression ultimately becomes practically
proportional to increase of pressure, and is slightly greater with the
former than with the latter.
The table gives representative results obtained on the same sheep-skin
(roan) in the limed and in the puered condition. These results are
expressed graphically in Fig. 12.
------------+--------------------------+-------
Load | Thickness in mm | Δ
per sq.cm. +------------+-------------+-------
in grm. | Limed skin | Puered skin |
------------+------------+-------------+-------
0 | 3·45 | 1·78 | 1·67
20 | 3·43 | 1·58 | 1·85
40 | 3·33 | 1·43 | 1·90
60 | 3·28 | 1·35 | 1·93
80 | 3·22 | 1·23 | 1·99
100 | 3·15 | 1·13 | 2·02
120 | 3·08 | 1·08 | 2·00
140 | 3·03 | 1·05 | 1·98
160 | 2·95 | 1·01 | 1·94
180 | 2·90 | ·98 | 1·92
200 | 2·83 | ·95 | 1·88
300 | 2·73 | ·88 | 1·85
All off | 2·98 | -- | --
380 | 2·61 | ·82 | 1·79
600 | 2·43 | ·76 | 1·67
All off | -- | ·76 | --
------------+------------+-------------+-------
Δ = difference in thickness of the skin--i.e. compression under the
same load.
[Illustration: Fig. 11.--Apparatus for Measuring Degree of Falling
_m_ = micrometer dial.
JJ = jaws between which the skin is placed.
_b_ = balance-weight attached to cord passing over pulleys _p p_,
to counterbalance weight of frame _f f_.
_k_ = knife edge supporting pan and weights _w_.]
Fig. 11 shows the apparatus[72] that was employed to obtain these
results. It consists essentially of a commercial form of micrometer
for measuring the thickness of leather. To one of its jaws a pan for
weights is attached, by means of the frame _f f_, in such a manner as
to secure a perfectly straight pull. The weights of the frame and pan
are counterbalanced in the manner shown by a counterpoise _b_. The
delicacy of measurement may be increased by inserting larger jaws in
the form of suitably fashioned disks, but even when this is done the
results are to a certain extent vitiated by the rather considerable
friction of the micrometer.
[72] The apparatus was constructed by Mr. W. Linney, of the
University College, Nottingham.
Since this apparatus was constructed Professor H. R. Procter has
informed me that an appliance devised by Mr. Anderson, of the Leeds
University, for measuring the thickness of leather under varying
pressures, has been in use in the leather industries department
for some months for the purpose of measuring the proportion of the
permanent to elastic compression.
[Illustration: Fig. 12.--Curve obtained by Measuring Apparatus.
(The dotted lines show the pressure on taking off the load.)]
An apparatus free from this fault is shown in Fig. 13. It consists
essentially of a counterbalanced lever A, to which the upper jaw J is
rigidly attached. By means of a sliding weight W, any desired load,
from zero upwards, may be put on this jaw. The lever carries a very
delicate spirit level, which allows it to be set accurately horizontal
in every experiment. The lower jaw is movable vertically between
parallel guides, and its position is controlled by the screw-wheel S
which bears a divided circle on its circumference. The position of this
wheel, and therefore of the lower jaw, may be accurately read on the
vernier _v_. In every experiment it is adjusted so as to make the upper
lever accurately horizontal.
[Illustration: Fig. 13.--Improved Apparatus for Measuring the Degree of
Falling. (Sand.)]
CHAPTER IV.
THE BACTERIOLOGY OF THE BATE.
“Omne vivum ex ovo.”--HARVEY (1578–1675).
When a drop of liquid from a puer wheel in use is examined under the
microscope[73] with 1/12 o.i. objective, it is seen to be swarming with
bacteria.
[73] A good microscope, with 1/12 oil-immersion objective and Abbe
condenser, is necessary for bacteriological work. The new dark-ground
condenser made by James Swift and Son, London, is extremely useful
for examining living bacteria under high magnifications.
The majority are short rods (bacilli), but other forms, cocci and
spirilli, are seen in lesser numbers. Most of these bacteria move
briskly in the liquid; as the temperature of the slide sinks, their
movements become slower, and finally cease. The illustration, Fig. 14,
shows the various forms of bacteria observed by the author in puer
liquors × 1000 diam.
[Illustration: Fig. 14.--Various Forms of Bacteria in Puer Liquors.]
The living bacteria are best examined in a drop culture in the
following manner. A clean cover-glass, of the proper thickness for the
objective to be used, is laid upon a black glass plate. With a platinum
loop, previously heated to redness in the flame, a drop of sterile
physiological salt solution (0·6 to 0·75 per cent.) or sterile broth
is placed in the centre of the cover-glass. With a platinum needle a
minute quantity of the puer liquor is stirred into the drop. A slide
with a depression in the centre is taken, the edge of the depression
painted round with vaseline, and pressed over the cover-glass, so that
the drop is exactly central. If the whole be now turned smartly over,
the drop will hang central in the hollow space.
If the ring of vaseline is continuous, and the cover well pressed
down, the drop is preserved from evaporation, and the bacteria may be
examined in their natural condition--best on the edge of the drop.
For illuminating the drop culture, the concave mirror is used, and a
small diaphragm without condenser; whereas, for stained preparations,
the flat mirror is used in conjunction with the Abbe condenser.
If the cover-glass be carefully removed, and dried under a bell glass,
the culture may be preserved in a dry condition, or may be stained and
mounted.[74]
[74] The most recent method is to preserve the slides without
cover-glasses: a drop of cedar oil is placed directly on the
preparation, and, after examination, carefully washed off with xylol.
Care should be taken not to touch the preparation with the fingers.
If the dried preparation is on a cover-glass, it should be held in the
fingers (prepared side upwards), and passed slowly three times through
the flame of a Bunsen burner. By holding the preparation in this way,
the exact temperature for proper fixation is obtained.
A drop of fuchsin stain, or gentian violet, is allowed to remain on the
preparation for five minutes; wash off the superfluous dye with water,
and examine, either in the wet state or after drying and mounting in
balsam.
[Illustration: Fig. 15.--B. Coli Commune. Stained to show Flagellae.]
For a detailed account of the technique of staining and mounting, the
following works may be consulted:--
Methods and Formulæ. P. W. Squire. (Churchill.)
Taschenbuch für den bakteriologischen Praktikanten. Dr. Rudolf
Abel. (Stubers-Verlag, Würzburg.)
Technique Microbiologique. Nicolle and Remlinger. (Octave Doin,
Paris.)
Practical Bacteriology. Kanthack and Drysdale. (Macmillan, London.)
The recent researches of Tissier and Metchnikoff have shown that
the flora of the intestines, both of men and animals, consist very
largely of anaerobic bacteria. These have been overlooked in previous
researches, owing to imperfect means of studying this class of
organisms. Indeed, in one work on the microbes of the alimentary canal
of the dog, no mention was made of them, whereas they are all very
active.
Most of these organisms, and the new methods by which they have been
isolated, are fully described in a new work entitled “Les Anærobies,”
by M. Jungano and A. Distaso, of the Pasteur Institute, Paris.[75]
[75] Masson et Cie, Publishers.
The following bacteria have up to the present been isolated from dung
(mostly dog dung), and studied in pure cultures:--
1. _Micrococcus ureae_ (Cohn). (Pasteur.)
2. " _fulvus_ (Cohn).
3. " _prodigiosus._
4. " _ureae liquefaciens._
5. _Bacterium sulphureum._
6. " _coli commune._ (Fig. 15.)
7. " _coli anindolicum._
8. _Bacterium coli anaerogenes._
9. " _furfuris_ α (Wood). (Fig. 30.)
10. " _furfuris_ β (Wood). (Fig. 31.)
11. _Bacillus fluorescens putridus._
12. " " " _liquefaciens._
13. " _subtilis._
14. " _saprogenes_ (Herfeld), three varieties.
15. " _butyricus_ (Hueppe). (Fig. 23.)
16. " _putrificus._ (Fig. 19.)
17. " _pyocyaneus._
18. " _janthinus._
19. " _coprogenes fœtidus._
20. " _pyogenes fœtidus_ (a variety of _B. coli_).
21. " _zenkeri._
22. " _magnus._
23. " _spinosus._
24. " _liquefaciens_ (Eisenberg, Frankland).
25. " _amylobacter_ (Van Tieghem).
26. " _acidi paralactici._
27. " {I. } Isolated from horse manure by Severin,
28. " {II. } Centr. Bl. f. Bakt. (2), i., 97.
29. " {III.}
30. " from horse dung (anaerobic) Severin, Centr. Bl. f.
Bakt. (2) iii., 708.
31. " from horse dung (anaerobic), No. 3, ditto.
32. " _oedematis maligni_ (Vibrion Septique, Pasteur).
33. " _mesentericus vulgatus._
34. " _lactis aerogenes._
35. " _cavicida_ (Brieger).
36. " _albuminis_ (Bienstock).
37. " _Bienstockii._
38. " _tenuis._
39. " _enteritidis sporogenes_ (Klein).
40. " _lactis acidi_ (Ankerschmid, 1905).
41. " _megatherium._
42. " _cadaveris sporogenes_ (Klein) said to be identical
with No. 16.
43. " _thermophilus._ (Houston).
44. " _a._ from puer. See p. 162.
45. " _b._ " " "
47. _Bacillus mycoides._
48–61. 14 species isolated from dog and pigeon dung by Prof.
H. Becker. Zeit. f. Offentlich. Chemie. Heft xxiii.
Jahrgang X. p. 447, includes _B. erodiens_ (Fig. 16).
62. _Sarcina fimentaria_ (Lehmann and Neumann).
63. _Streptococcus_ from sewage. (Houston.)
64. " _brevis._
65. " _longus._
66. " _pyogenes._
67. " _liquefaciens coli._ (Gamgee Phys. Chem. 2.)
68. _Streptothrix_ from stable manure. (Severin, 6.)
69. _Spirillum serpens_ (Kutscher).
70. " _tenue_ "
71. " _undula_ "
72. " _volutans_ " (Figs. 24 and 25).
73. " from pig dung. Smith, Centr. Bl. f. Bakt. 16, (1),
124
74–76. _Vibrio_, three species isolated by Kutscher.
77. _Clostridium butyricum_ (Prazmowski), said to be identical with
No. 25.
78. _Streptococcus faecalis._ Sidney Martin, 37 and 38; Ann. Rep.
Loc. Gov. Board, 1907–9; Nature, March 3, 1910, p. 22.
79. _Bacillus bifidus._
80. " _perfringens._
81. " _bifermentans._
82. " _funduliformis_ (Veillon).
83. " _capillosus._
84. " _sporogenes._
85. " _ventriosus._
86. " _rodella III._
87. _Staphylococcus parvulus._
88. _Diplococcus orbiculus._
89. _Coccobacillus preacutus._
90. _Coccobacillus oviformis._
91. _Bacillus faecalis alkaligenes_ (Petruschky).
(79–90 are anaerobic bacteria, described and figured by
Jungano and Distaso.)
It will be surmised from the above list, to which additions are still
being made, that the flora of the intestines is pretty extensive, and,
consequently, the study of the part played by the various species of
bacteria is a long and difficult one.
The methods of isolating these bacteria, and the compositions of the
media employed, would demand a treatise on bacteriology; but, for
general purposes, a good liquid medium for the cultivation of puer
bacteria is a gelatin peptone broth, made by digesting 10 grm. gelatin
with 6-1/2 grm. 80 per cent. lactic acid in 100 c.c. water under
pressure for three hours, neutralizing with ammonia, adding 1 grm.
potassium phosphate, making up to 1000 c.c., and filtering. A sterile
infusion of fresh dung may be used, but it is troublesome to prepare
and not easy to get uniform in strength or composition. The culture
liquids are left slightly alkaline, an alkalinity equal to 0·0636 per
cent. Na_{2}CO_{3} or 12 c.c. N/1 soda per litre. The amount of alkali
may be increased to 0·15 per cent. Na_{2}CO_{3} without affecting the
growth of the bacteria. Of solid media, 10 per cent. nutrient gelatin,
or in summer 15 per cent., is good if used at temperatures below 25° C.
For higher temperatures, up to 39° and 40°, nutrient agar is required.
The best nutrient gelatin for general work is made according to Klein’s
formula.[76] For media in general, a most useful compendium is Abel’s
Taschenbuch.
[76] Klein, E., Micro-organisms and Disease (Macmillan), p. 22. See
also, Kanthack and Drysdale, Practical Bacteriology (Macmillan 1896),
p. 86.
The number of bacteria in fresh fæces varies greatly, but is of the
order of 10,000,000 per grm. of dry matter, capable of developing in
nutrient gelatin. Of this number, about 100,000 are spore-bearing
organisms. This estimate applies to healthy animals; in a diseased
condition, the numbers vary enormously.
Dr. A. C. Houston found in raw London sewage from 3,000,000 to
9,000,000 microbes per c.c., of which more than one-tenth were
gelatin-liquefying organisms. There were only about 300 spores of
aerobic bacteria, about 100,000 B. coli, 100 B. enteritidis sporogenes,
and streptococci, in one gram of fæces.
With the object of ascertaining the effect of the various species of
bacteria contained in the dung upon skins, a large number have been
isolated, and the effect of pure cultures in different media has been
tried upon skin.[77] A number of the results have been published in
the Journal of the Society of Chemical Industry. Professor H. Becker,
who has done a great deal of this part of the work, is of opinion that
the principal organisms concerned in the bating exist in the dog’s
intestines, and belong to the group of coli bacteria. These are very
widely distributed bacteria, and are found in the large intestines of
mammals, and, as a consequence, in almost all soils, and in the mud of
rivers and lakes. The principal variety is B. coli commune.
[77] The subject is not so far removed from direct human interest as
one might suppose. For many years Metchnikoff, in Paris, has been
studying the bacterial flora of the human intestines. His theory is,
that old age is caused by the poisonous products of these intestinal
bacteria, and he proposes to counteract the effects of these
poisonous organisms, by introducing into the system large quantities
of lactic acid bacteria, either in the form of tabloids, or in the
form of sour milk cultures.
Lortet found it, along with other organisms, in the mud of the Lake of
Geneva, at a spot where the water was chemically very pure. Dr. A. C.
Houston, the bacteriologist of the Metropolitan Water Board, enumerates
sixteen varieties of this organism, 80 per cent. of which produced acid
and gas in lactose-peptone cultures, indol in peptone-water cultures,
and when grown in milk produced acid and clot. The bacterium (Fig. 15)
resembles that of typhoid fever, and has frequently been mistaken for
it. It is, however, much more resistent to destructive influences. It
is a short bacillus, possessing flagellae, by which it moves more or
less rapidly.
B. coli forms short rods 0·8 µ wide, 1 to 3 µ long. It moves somewhat
slowly by means of flagellæ, which may be demonstrated by staining with
Loffler’s method.[78] It grows equally well in absence or presence of
air, that is, it is a facultative anaerobe. Although it will grow at
room temperature, the optimum growth is at 37° C. In plate cultures the
appearance of the colonies below the surface of the gelatin is quite
different from that of the surface colonies. The former are small
round colonies, about the size of a pin head; the latter spread into a
whitish iridescent film, with irregular edges.
[78] For the demonstration of flagellæ, the material is taken from
a culture on solid media--a young agar culture is best. Make a
dilution by Soyka’s method (p. 103), dry and fix on a cover-glass as
described, p. 88, then proceed as follows:--
1. Mordant with a mixture of 10 c.c. 20 per cent. tannin solution,
5 c.c. cold saturated ferrous sulphate, 1 c.c. fuchsin or wool-black
solution. This solution is put on the preparation, which is then
heated for one minute until steam is given off.
2. Wash under the tap, then in alcohol.
3. Stain with anilin-water-fuchsin solution, prepared by dissolving
the dye in anilin-water and adding 1 per cent. of a 1 per cent.
solution of caustic soda until the liquid begins to go cloudy.
4. Wash off the stain with distilled water.
B. coli does not liquefy the gelatin. When grown in nutrient solutions
containing sugars, it produces much acid, and at the same time gases
are given off, consisting of CO_{2} and hydrogen. If the growth in this
solution be allowed to continue a secondary fermentation ensues, and
the culture eventually becomes alkaline.
Indol is produced by B. coli, and may be demonstrated by adding to
10 c.c. of the culture, 1 c.c. of a 1/50 per cent. solution of pure
potassium nitrite; then adding a few drops of concentrated sulphuric
acid, when, if indol be present, a red coloration (nitroso-indol) is
produced. This bacterium reduces nitrates to nitrites. Cultivated
in a 1 per cent. solution of peptone, to which 1/10000 per cent. of
potassium nitrate has been added, after four hours at 37° C., the
presence of nitrite may be shown; after the growth has continued for
seventeen hours, the nitrite is further reduced to ammonia. Among other
products of B. coli, Harden found lactic, formic, acetic, and succinic
acids, ethyl-alcohol, CO_{2} and hydrogen.
In Germany, W. Lembke and H. Becker have specially investigated the
bacterial flora of the dog’s intestines. Lembke, in 1896[79] cultivated
the bacteria from the fæces of the dog, fed in various ways--bread,
meat, and fat diet--and found B. coli constantly present, although the
form of the individuals, as well as the colonies, and the intensity of
the indol and gas formation, showed great variations.
[79] “Beitrag zur Bakterienflora des Darmes,” Archiv f. Hygiene, Bd.
26, p. 293.
The other species of bacteria present varied with the kind of food;
this has a great influence on the flora of the intestines, which was
found to be very different when the dogs were fed on bread to what it
was when they were fed on meat.
Lembke describes two other species of bacteria closely resembling B.
coli, one of which he calls B. coli anindolicum, which, as the name
implies, gives no indol reaction; the other, B. coli anaerogenes, is
non-motile, possesses no flagellæ, and differs from B. coli by the
absence of gas production in the fermentation of sugars.
Besides B. coli, there are several species of bacteria which liquefy
gelatin, and a number of facultative organisms, whose presence is
more or less accidental. By changing the food, and introducing with
it quantities of foreign organisms, the composition of the intestinal
flora may be changed. By introducing for a considerable period B. coli
anindolicum, Lembke succeeded in entirely suppressing B. coli commune.
On returning to normal feeding, the foreign organisms in some cases
entirely disappeared.
The researches of Dr. H. Becker[80] were applied more directly to
the use of bacterial cultures for the bating of skins, and to the
elucidation of the bacterial action of dog-dung infusions. He isolated
54 varieties of bacteria from dog-dung, and tried the action of pure
cultures of many of them on a skin.
[80] Zeit. f. Offt. Chem., Heft. xxiii. Jahr. X. p. 447.
A list of the various bacteria isolated by Becker is given in tabular
form on pp. 98–101.
[Illustration: Fig. 16.--B. Erodiens (Becker).]
[Illustration: Fig. 17.--Plate Culture from Fresh Puer.]
Professor Becker’s Bacterium No. 12, which he has named Bacillus
erodiens (Fig. 16), is undoubtedly a variety of B. coli, but has a
more rapid motion, and does not coagulate milk, although it renders it
somewhat thick. Cultivated in broth it gives off much gas, consisting
of 12 per cent. carbon dioxide, 85 per cent. hydrogen, 3 per cent.
oxygen. If glucose be added, the quantity of carbon dioxide rises to 40
per cent., and acid is produced. The most rapid growth is at 37° C.,
and at this temperature a broth culture has a distinct reducing action
on skin. According to the medium in which it is grown, it produces
acid or alkali, and thus comes under the heading of mixed bacteria. In
sugar[81] solutions acid is produced, and in proteid solutions ammonia
compounds, indol, and evil-smelling gases are given off. Thus, by
varying the medium, the effect produced may also be varied.
[81] Dr. A. C. Houston has been kind enough to make an examination
of B. erodiens, and to ascertain its action on various sugars. It
produces fluorescence in neutral-red broth cultures, acid and gas
in lactose cultures, indol, and acid, and clot in milk cultures.
It ferments dulcite with production of acid, but _not_ cane sugar,
adonite, inulin, inosite, salicin, or raffinose.
B. erodiens does not secrete any tryptic enzymes, hence its action
on the skin is to be attributed either to an intracellular enzyme,
or to its chemical products, which, being secreted _in situ_, have
a more favourable and powerful action than if merely added to the
bating liquid. It was for this reason that I proposed to use a mixed
culture of bacteria, especially bacteria from the sweating process (see
p. 105), which secrete a mild form of proteolytic ferment, capable
of dissolving the more easily soluble portion of the skin fibres (or
certain constituents), but not capable of attacking the hyaline layer.
--------+-------+-------------+--------+---------------------------+------------
No. of | | Shape | | | Growth
the Bac-| Where | and |Motility| Growth on Gelatin | on
terium | Found | Arrangement | | | Agar-agar
--------+-------+-------------+--------+-----------------------------------+----
1 |Dog |Small rods |Lively |In the gelatin stab-culture|A white
|dung |of the size | |the bacteria show a good |surface
| |of the _Bac. | |growth in the depth. At the|layer is
| |prodigiosus_.| |surface it forms a small |formed on
| | | |white button. The gelatin |inclined
| | | |is not liquefied. The col- |stiffened
| | | |onies which have reached |agar-agar.
| | | |the surface of the gelatin-|
| | | |plate spread in the shape |
| | | |of a leaf, with a mother- |
| | | |of-pearl-like gloss. |
| | | | |
2 | Do. |Small rods of| Do. |Stab-culture: The germs |A yellowish-
| |the size of | |develop along the entire |white layer
| |the hay | |track. Small arms extend |is formed
| |bacillus. | |sideways into the gelatin. |along the
| | | |A white layer is formed on |inoculating
| | | |the surface. The gelatin is|stab.
| | | |slowly liquefied. |
| | | | |
| | | |Gelatin-plate: When they |
| | | |reach the surface, the col-|
| | | |onies spread out in the |
| | | |shape of a leaf and then |
| | | |are slightly fluorescent. |
| | | | |
3 | Do. |Very small | Do. |Stab-culture: Very good |A white
| |rods rounded | |growth in depth. Very many |deposit is
| |at the | |arms extend laterally from |formed on
| |ends. | |the track of the stab into |inclined
| | | |the gelatin. Small knots |agar-agar.
| | | |are formed at the ends of |
| | | |the arms. A thin white |
| | | |coating is formed on the |
| | | |surface. Gelatin is not |
| | | |liquefied. |
| | | | |
| | | |Gelatin-plates: The colon- |
| | | |ies located deeper down |
| | | |appear as pale-yellow small|
| | | |round disks, which gradual-|
| | | |ly work up toward the sur- |
| | | |face and there form circu- |
| | | |lar disks which show larger|
| | | |dots in the middle. |
| | | | |
4 | Do. |Small rods as|Slow |The gelatin stab-culture |Heavy white
| |large as hay |movement|resembles that of the hay |deposit on
| |bacilli. | |bacillus, while the growth |the entire
| | | |in the gelatin-plate more |surface.
| | | |resembles that of the an- |
| | | |thrax bacillus. Threads ex-|
| | | |tend from the liquid colon-|
| | | |ies which have been let in,|
| | | |which threads are at first |
| | | |braided and twisted, and |
| | | |later on extend straight |
| | | |into the gelatin. |
| | | | |
7 | Do. |Small rods |Lazy |Stab-culture: Strongly li- |White
| |similar to | |quefying. A white skin |unevenly
| |the hay | |forms on the surface. Along|thin layers
| |bacillus. | |the liquefied prick are ra-||withspurs.
| | | |diations into the solid |
| | | |gelatin. |
| | | | |
| | | |Gelatin-plate: Quickly li- |
| | | |quefying colonies which |
| | | |form a white skin at the |
| | | |top. |
| | | | |
11 | Do. |Medium-sized |Motile |Stab-culture: A white coat-|A white
| |small rods. | |ing is formed on the sur- |deposit
| | | |face. The gelatin is not |along the
| | | |liquefied. The bacteria |puncture.
| | | |grow well in the depth. |
| | | | |
| | | |The colonies which come to |
| | | |the surface spread out |
| | | |leaf-like with a mother-of-|
| | | |pearl-like gloss. |
| | | | |
12 |Dog |Medium-sized |Lively |Stab-culture: Grows evenly |Heavy white
|dung |small rods. | |along along the track. Ge- |deposit;
| | | |latin is not liquefied. A |glossy.
| | | |thin glossy deposit on the |
| | | |surface. |
| | | | |
| | | |Gelatin-plates: The lower- |
| | | |lying colonies appear as |
| | | |pale-yellow circular small |
| | | |disks. Braids are noticed |
| | | |in some colonies similar to|
| | | |the superficial colonies of|
| | | |_Proteus_. Strong decaying |
| | | |smell. |
| | | | |
13 | Do. | Do. |Motile |Stab-culture: A thin coat- |White
| | | |ing forms on the surface. |deposit
| | | |The bacteria grow downward |along the
| | | |bristle-like. Small buttons|puncture.
| | | |are formed at the ends of |
| | | |the bristles. |
| | | | |
| | | |Gelatin-plates: Leaf-like, |
| | | |mother-of-pearl glossy, |
| | | |spreading. |
| | | | |
38 |Pigeon |Small rods |Lively |Stab-culture: Bag-shaped |Yellow
|and | | |liquefying of the gelatin, |spreading
|poultry| | |thesame being coloured |over the
|dung. | | |yellow. |surface of
| | | | |the culture
| | | |Gelatin-plates: The deep- |medium.
| | | |seated colonies are gran- |
| | | |ular, yellow. Those that |
| | | |have forced their way to |
| | | |the surface form white |
| | | |glistening small buttons. |
| | | | |
40 | Do. | Do. | Do. |Stab-culture: A white heavy|White
| | | |deposit is formed on the |irregular
| | | |surface of the culture me- |deposit.
| | | |dium; grows very well along|
| | | |the track. |
| | | | |
| | | |Gelatin-plates: Leaf-like |
| | | |deposits with line system. |
| | | | |
42 | Do. | Do. | Do. |Stab-culture: A white heavy| Do.
| | | |Spreading. Very good growth|
| | | |along the prick. |
| | | | |
| | | |Gelatin-plates: Leaf-shaped|
| | | |deposits with line system. |
| | | | |
43 | Do. |Large, |Not |Stab-culture: The gelatin |White
| |grouped, |motile |is slowly liquefied. Only |puncture
| |grape-like. | |slight growth in the depth.|in yellow.
| | | |The culture medium is col- |
| | | |oured chamois colour. |
| | | | |
| | | |Gelatin-plates: Yellow |
| | | |disks. |
| | | | |
44 |Pigeon |Small rods, |Lively |Stab-culture: A heavy white|White
|and |quite | |spreading on the surface. |irregular
|poultry|different | |Very good growth along the |deposit.
|dung. |in size. | |prick. |
| | | | |
| | | |Gelatin-plates Leaf-shaped |
| | | |deposits with the line sys-|
| | | |tem. |
| | | | |
45 | Do. |Small rods | Do. |Stab-culture: A heavy white|Very thin
| | | |spreading on the surface. |deposit.
| | | |Slight growth only in |
| | | |depth. |
| | | | |
| | | |Gelatin-plates: Leaf-shaped|
| | | |depositwith clear line sys-|
| | | |tem. The entire colonies |
| | | |appear much thinner than |
| | | |those of the preceding |
| | | |numbers. |
--------+-------+-------------+--------+---------------------------+------------
[table continued]
--------+-----------+----------+------+-------------------+---------------------
No. of | Growth | Growth | Best | Development |
the Bac-| on | in |Growth| of | Special Remarks
terium | Potatoes | Milk | at-- | Gas |
--------+-----------+----------+------+-------------------+---------------------
1 |The bacter-|Milk is |37° C | Only slight |Without doubt a var-
|ium shows |not | | |iety of bacterium
|only a weak|changed | | |_Coli commune_.
|growth on | | | |
|potatoes. | | | |
|It forms a | | | |
|yellow | | | |
|layer. | | | |
| | | | |
2 |Dirty |Milk |Room |Does not occur | --
|yellowish |remains |temp. | |
|layer. |unchanged.| | |
| | | | |
3 |Yellowish |Milk is |37° C |Very pronounced. |Culture-medium to
|deposit |caused to | |From fifty cubic |which blue litmus
|at the |curdle | |centimeters of |is added turns red.
|place of |only after| |broth 6·5 cubic |
|inocula- |it has | |centimeters gas |
|tion. |been in | |were produced in |
| |the incu- | |fifteen hours, of |
| |bator for | |which 3·5 per cent.|
| |four days.| |was oxygen, 10·7 |
| | | |per cent. carbonic-|
| | | |acid gas, and 85·8 |
| | | |per cent. nitrogen.|
| | | | |
4 |White, dry,|Milk is | Do. |Does not occur | --
|spreading. |changed. | | |
| |Serum is | | |
| |separated | | |
| |out. | | |
| | | | |
7 |White, dry.|Strong | Do. | Do. | --
| |serum | | |
| |formation.| | |
| | | | |
11 |Yellowish |Milk | Do. |Weak |Strongly resembles
|glossy |curdles | | |the bacterium_Coli
|deposit. | | | |commune_ and differs
| | | | |therefrom only in
| | | | |that the milk
| | | | |curdles quicker.
| | | | |
12 |Yellowish |Milk |37°C |Considerable. Five |If 0·25 cubic centi-
|glossy |becomes | |cubic centimeters |meters of broth-
|covering. |pappy. | |of gas will be de- |culture are injected
| | | |veloped from fifty |under the epigastri-
| | | |cubic centimeters |um, the animal is
| | | |of common broth in |taken violently ill.
| | | |an incubator during|After four hours
| | | |the first fifteen |violent diarrhea
| | | |hours and six cubic|occurs. Soon the
| | | |centimeters during |mouse can hardly move;
| | | |the first forty- |looks bristly. On the
| | | |eight hours, con- |third day the animal
| | | |sisting of 12·12 |dies. On opening the
| | | |per cent. carbonic |body a strong putrid
| | | |acid, 3 per cent. |smell is noticed.
| | | |oxygen, and 84·9 |Some of the injected
| | | |per cent. hydrogen.|bacteria are found in
| | | |The gas obtained |the blood. The intes-
| | | |from a culture- |tines are coloured
| | | |medium containing |green and black.
| | | |grape-sugar |The other organs are
| | | |contains about 40 |pale.
| | | |per cent. carbonic |
| | | |acid. |
| | | | |
13 |Glistening,|Strong | Do. |Weak |In old stab-cultures
|yellowish. |curdling. | | |a brown discoloration
| | | | |of the culture-bed is
| | | | |noticed along the
| | | | |length of the stab.
| | | | |Differs in the gelatin
| | | | |stab-culture from the
| | | | |common bacterium _Coli
| | | | |commune_likewise in the
| | | | |curdling of the milk.
| | | | |
38 |Yellow |Milk | Do. |Not noticed | --
|glistening |is not | | |
|deposits. |changed. | | |
| | | | |
40 |White, | Do. | Do. |Weak. Is only | --
|glistening.| | |noticed in culture-|
|Only very | | |bed containing |
|slight | | |grape-sugar. |
|growth. | | | |
| | | | |
42 |Sulphur |No change | Do. |Strong only in | --
|yellow, |of the | |media containing |
|glistening.|milk. | |grape-sugar. |
| | | | |
43 |No growth | Do. | Do. |None | --
| | | | |
44 |Weak devel-|Curdling | Do. |Very weak. Only in |
|opment. The| | |media containing |
|culture is | | |grape-sugar. |
|sulphur | | | |
|yellow. | | | |
| | | | |
45 |Weak |Milk is | Do. |Not noticed | --
|yellowish |not | | |
|deposit. |changed. | | |
--------+-----------+----------+------+-------------------+---------------------
The practical difficulty is to keep such cultures uniform during
propagation, and so far this has prevented their introduction in
practice. Similar difficulties have influenced the use of pure cultures
of yeast in the brewing of English beers, although the use of a single
species of yeast is common in the low fermentation breweries on the
Continent.
I found in studying the bacteria of dog dung, that the species existing
in the _fresh_ dung, which developed in ordinary plate cultures,
appeared to belong to four or five species only, mostly bacilli. At
the end of two or three weeks, the original species had given place to
others, mostly cocci, in a very similar way to the change which takes
place in putrefaction. In fact, many of the organisms are identical
with those which cause putrefaction. It will be seen, therefore, that
no single species produces the complex chemical and physiological
changes which take place, or the bodies necessary for the bating of
skin, as some observers have supposed; but the various species succeed
one another as the medium changes its reaction and composition,
until finally the organic portion is resolved into the simplest
bodies such as carbon dioxide, ammonia, and hydrogen. There is thus
a moment when the dung is at its best so far as the bating action is
concerned, and this moment is due to the vital activity of bacteria,
and consequently varies according to the temperature and some other
influences (electrical condition of the atmosphere, etc.). One may say
it is at its best at about fifteen days in summer, and one month or
more in winter. Puer which has been dried, is not so powerful in its
action as that which is immediately made into a paste with water. It
appears to lose its “nature,” partly owing to irreversible dehydration
processes, and partly because some of the bacteria are killed. Plate
cultures on agar from fresh puer (Fig. 17), and from a puer wheel in
use (Fig. 18), show the number of bacteria in the puer wheel to be much
greater than in the fresh puer. Whence it is evident, that the bacteria
continue to develop in the puer and to produce their various products,
enzymes, etc. We have already considered the action of the chemical
products, and in Chapter V. we propose to discuss the action of enzymes.
[Illustration: Fig. 18.--Plate Culture from Puer Wheel.]
[Illustration: Fig. 19.--B. Putrificus.]
*Pigeon-Dung Bate as used for Hides.*--The bacteria contained in the
intestines of birds and in bird dung have not been studied to the same
extent as those of mammals, so that it is not possible to give anything
but a meagre account of them. A microscopical examination of fresh
pigeon dung, collected on a sterile Petri dish, showed debris of food,
cellulose, etc., among the debris, a large number of dumb-bell bacteria
(_b_) (Fig. 20), and a few motile pairs (_c_); no bacilli were seen.
Cells of a saccharomyces (_a_) were also observed. From this pigeon
dung attenuations were made by a modification of Soyka’s method,[82]
and from the fourth attenuation a plate culture was made in ordinary
nutrient gelatin. The colonies from this plate were principally of
two varieties (both non-liquefying organisms), corresponding to the
bacteria observed in the original dung. Large cultures were made in a
Carlsberg vessel, as described in Chapter VI., and the effect of these
cultures tried upon skin. No particular reducing effect was obtained.
[82] The modification of Soyka’s method of making attenuations of
bacteria is that of Günther (Bakteriologie, 1898, p. 204), and
is carried out as follows:--On the inner surface of the cover of
a sterile Petri dish (which is to be used for making the plate
culture), place four drops of sterile broth, or sterile water;
inoculate the first drop, by means of a platinum needle, with the
material to be examined; heat the needle in the flame, dip it into
the first drop, and, with the liquid adhering, inoculate the second
drop. Proceed in this way, each time heating the needle, to the
fourth drop. From this fourth drop a tube of nutrient gelatin is
inoculated, and poured on to the plate. The cover is then put on, and
the plate put into the incubator. The drops on the cover do not in
any way contaminate the culture.
[Illustration: Fig. 20.--Organisms in Pigeon Dung. × 1000.]
A microscopical examination of a bating pit used for kips, showed an
extraordinary mixture of bacteria, bacilli, vibrios, and monads; some
comparatively large dumb-bell shaped bacteria, very motile, were
present. The difference between the bating liquor and the fresh dung
was very marked, especially in the variety of species present. Cultures
made from several colonies isolated from the above bate, in a nutrient
liquid, consisting of 10 litres water, and 20 grm. gelatin, peptonized
by heating under pressure with 10 c.c. sulphuric acid, afterwards
neutralizing with ammonia, and adding the soluble matter from 200 grm.
bone-meal, had no action on skin.
It would be unsafe to say from these two experiments that the bacterial
effect of the pigeon-dung bate is negligible, but we may assume that it
is different and not so great as with the dog-dung bate or puer.
A complete research as to the various species of bacteria developing in
the bird-dung bate is necessary before this question can be answered.
*General Considerations on the Growth of Bacteria in Various
Media.*--Since the publication of Further notes on the action of the
dung bate (Chapter VI.), I have found that the bating organisms grow
better in the special medium, when it is neutralized with ammonia, than
when it is neutralized with sodium carbonate, i.e. the presence of
organic ammonium salts is more favourable to the growth of the bacteria
than the corresponding sodium salts.
I also found that bacteria obtained from other sources than dung,
viz. from the roots of wool just beginning to “slip” in a sweating
stove, were equally effective in causing the skin to fall. Now these
bacteria produce ammonia, and it seems clear that they are essential
to the chemical part of the process. They also produce proteoclastic
enzymes, which act upon the skin fibre (see chapter on Enzyme Action).
The products of the bacteria depend very much upon the composition of
the nutrient medium. Many organisms grown in media containing sugar
or other carbohydrates produce acids, but, grown in proteids free
from sugars, they produce alkaline compounds. Villon (“The Leather
Industry,” 1901, p. 408) describes a bacterium which he considers to be
the special micro-organism concerned in the depilation of skins, which
resembles Bacillus _d_ (Wood) (Fig. 21), but he does not describe the
appearance of the cultures; he states, however (p. 410), that this is
the only bacterium which can develop in the limes,[83] and that it is
the cause of the unhairing in this case also. Since the production of
ammonia in limes is known to be due to bacterial action, it is very
probable that this bacterium, which is ubiquitous, is also of use in
the bate, and a research in this direction would be interesting.[84]
[83] Villon found that Bacterium pilline developed 0·142 per cent.
ammonia in ten days in lime liquors used for unhairing skin.
[84] Cultures made from old limes have, however, not been found
effective in bating.
Some of the fermentations taking place in the dung come under the
heading of putrefactive processes (see p. 116). Tyrosin is formed in
considerable quantities during putrefactive fermentation, but is soon
further decomposed, according to Nencki, with formation of indol,
CO_{2} and hydrogen. Leucin gives valerianic acid, ammonia, CO_{2} and
hydrogen; nitrogenous bodies of the aromatic series are also produced.
[Illustration: Fig. 21.--Bacillus _d_.]
[Illustration: Fig. 22.--Bacillus _e_.]
Bacillus ureaæ, B. prodigiosus, and B. fluorescens putridus, evolve
trimethylamine (Herfeldt), and, as the writer has shown, this amine has
an important action in the puering process. In combination with organic
acids, it removes lime from the skin, and in addition it favours the
growth of bacteria, such as bacillus _d_ and _e_ (Figs. 21 and 22) and
B. coli.
The albumens and peptones of the dung are pretty well decomposed
and absorbed before evacuation; the bacteria subsequently split up
the amido acids into fatty acids and ammonia. The fatty acids are
then decomposed generally in the form of the calcium salts, in the
manner shown in the table (p. 108), for which I am indebted to Dr. E.
Herfeldt, of Bonn.
We have already treated of the action of these various products in
Chapter II., but it will be seen from what has been said in the present
chapter that the chemistry and bacteriology of the puer overlap, and
that it is difficult, if not impossible, to separate them entirely.
The bacteria are continually manufacturing chemical compounds, and
decomposing others.
In this respect it is interesting and instructive to note that Nencki,
in his classical work “The Chemical Mechanism of Putrefaction,”[85]
considers the processes by which the putrefaction of proteids is
brought about by bacteria, to be analogous to those taking place by
melting the bodies with potash, and he holds the view that in the
hydration processes brought about by bacteria, the water plays the same
part as the potash.
[85] Journ. f. Prakt. Chem., Bd. xvii., 1878; see also Stoklasa,
Cent. Bl. f. Bakt. vi., p. 526.
---+-------------+--------------+---------------------+----------------
No.| Fermenting | Cause of | Fermentation | Authors.
| Substance. |Fermentation. | Product. |
---+-------------+--------------+---------------------+----------------
1 |Calcium |Bacteria from |_Calcium carbonate, |Hoppe-Seyler,
|formate |sewer slime. |CO_{2} and H_ |Archiv f. d. g.
| | | |Physiol. xii.
| | | |
2 |Calcium | " " |_Calcium carbonate, | " "
|acetate | |CO_{2} and CH_(4)_ |
| | | |
3 |Calcium |Thin bacillus |1. _Propionic acid_, |Fitz, nine
|lactate | |and, as by-products, |papers in
|Undergoes | |_acetic acid_, |the “Berichte
|four | |_succinic acid_ and |der Deutsch.
|different | |_alcohol_. |Chem.
|fermentations| | |Gesellschaft,”
| |Other species |2. _Propionic acid_ |1876–1884.
| |of bacteria: |and _valerianic |
| |short aerobic,|acid_. |
| |butyric | |
| |bacteria |3. _Butyric acid_ and|
| |(Fitz). |_propionic acid_. |
| | | |
| | |4. _Butyric acid_, |
| | |according to Pasteur |
| | |(Comptes rend. 1861) |
| | | |
4 |Calcium |Bacteria |1. Chief product, |Schützenberger,
|malate |(not |_propionic acid_; |“Fermentation,”
| |described). |and, as by-product, |1876.
| |Thin bacilli. |_acetic acid_. |
| | | |
| | |2. Chief product, |
| | |_succinic acid_; |
| | |and, as by-product, |
| | |some _acetic acid_. |
| | | |
| | |3. _Butyric acid_ |
| | |and _H_. |
| | | |
| |Bacteria |4. _Lactic acid_ |
| | |and _CO_{2}_. |
| | | |
5 |Calcium |Different |1. Chief product, | " "
|tartrate |species of |_propionic acid_; |
| |bacteria. |by-product, _acetic |
| | |acid_. |
| | | |
| | |2. _Butyric acid_. |
| | | |
| | |3. Chief product, |
| | |_calcium acetate_; |
| | |by-products, _ethyl |
| | |alcohol_, _butyric_ |
| | |and _succinic acids_.|
| | | |
6 |Calcium |Small, thin |_Acetic acid_ in |Fitz.
|citrate |bacilli |large quantities, |
| | |along with small |
| | |quantities of _ethyl |
| | |alcohol_ and |
| | |_succinic acid_. |
| | | |
7 |Calcium |Micrococci |1. _Calcium acetate_,| " "
|glycerate | |along with small |
| | |quantities of |
| | |_succinic acid_ |
| | |and _ethyl alcohol_. |
| | | |
| |Medium-sized |2. _Formic acid_, |
| |bacilli |with some _methyl |
| | |alcohol_ and _acetic |
| | |acid_. |
---+-------------+--------------+-------------------+----------------
Nencki explains, for example, the metamorphosis of leucin by
putrefaction in this way: The bacteria decompose the water into
hydrogen and hydroxyl, which act upon the leucin as follows:--
CH_{3}
\ OH
CH - CH_{2} - CH - COOH + H = NH_{3}
/ |
CH_{3} |
Leucin NH_{2}
+ OH - CH_{2} (CH_{2})_{4} COOH (oxycaproic acid)
The resulting oxycaproic acid is then split up by the second water
molecule into methylenglycol and valerianic acid:--
OH
|
CH_{2} OH
| + H = CH_{2} (OH)_{2} + CH_{3} (CH_{2})_{3} COOH
(CH_{2})_{4}
|
COOH
The methylenglycol, which changes into formaldehyde and water, is now
split up into CO_{2} and hydrogen, as it would be by melting with
caustic alkali.
OH
H H.OH /
C O + = CO + 2H_{2}
H H.OH \
OH
As we shall see in the chapter on the action of enzymes, the phenomena
are of a catalytic nature. Any urea present is decomposed, by the
direct action of micrococcus ureæ, into ammonium carbonate and ammonium
carbamate, so that it does not play any part in the bating process as
usually carried out with dung which has been kept for some time, but
the ammonia produced plays an important part in the chemical action of
the bate, as we have already seen.
If, however, dung containing the urinary products be used in a fresh
condition, the urea has indirectly a very important influence on the
bating, as it favours the permeability of the skin fibre. (See p. 72.)
The fermentation of the cellulose in the dung has not been studied from
the bating standpoint, but it is well known that it is fermented by
various species of bacteria, which have been grouped together under the
generic name of Amylobacter.
Deherain and Gayon first showed that the solution and fermentation of
cellulose in the form of dead vegetable matter, which had previously
been observed, also took place in dung. Van Tieghem, in 1879, showed
that the solution of cellulose is caused by bacteria, whose properties
correspond with those described by him as Amylobacter. Tappeiner was
able to ferment cellulose by mixed cultures of bacteria from the
intestines of oxen--in neutral solution, CO_{2}, methane, H_{2}S,
aldehyde, butyric acid, and acetic acid, were all recognized. In
alkaline solutions, the principal products were CO_{2} and hydrogen,
together with the same by-products as before.
From the researches of Van Sennis, in 1890, it seems pretty certain
that the fermentation of cellulose is due to the symbiotic action of
at least two different organisms The decomposition of the cellulose
may be explained by considering that first a sugar-like carbohydrate
is formed by hydrolysis, and that this is then split up into equal
volumes of CO_{2} and CH_{4}. It may be noted that the fermentation
is anaerobic, and no doubt, so far as bating is concerned, the chief
products are the organic acids produced, principally butyric and acetic
acids. Van Sennis nearly always found Clostridium butyricum associated
with this fermentation.[86]
[86] Proc. Roy. Soc., lxvii., 1900.
Another group of organisms which have some influence in the bating
process, are the class called by Beijerinck, Granulobacter. They
produce butyric acid, and this acid, combining with the ammonia
compounds of the dung, forms salts which undoubtedly exert an effect on
the lime in the skins, though its action on the fibre is, perhaps, not
so great as the compounds of lactic and propionic acids.
The most common butyric ferment is the old Clostridium butyricum,
now known as B. butyricus, (Prazmowsky), which is anaerobic. It
forms spindle-shaped spores, hence the name Clostridium (from
_κλωστηρ_κλωστηρ, a spindle). Another species (Fig. 23), found in milk
by Hueppe (1884), is aerobic, and ferments lactic acid and its salts
to butyric acid, CO_{2}, and hydrogen; it appears to correspond with
Granulobacter polymyxa of Beijerinck.
Oxalic acid is known to be produced by some bacteria and the moulds
Penicillium and Sclerotinia, and in the white rot of the turnip it is
produced by Pseudomonas; it is also produced by some saccharomycetes,
such as B. Hansenii.[87] There is reason to believe that its
production plays a part in the bate, as we have already mentioned in
Chapter II., but the organisms producing it and their mode of action
still remain to be investigated.
[87] Reynolds Green, Fermentation, p. 350.
There are, of course, a large number of putrefactive bacteria in the
puer, among these B. putrificus (Fig. 19), isolated by Bienstock; it
is a spore-bearing anaerobic bacillus, and is interesting as specially
attacking fibrin. Now fibrin is extremely resistant to the action of
most putrefactive bacteria, and it is very probable that specific
organisms ferment the different albuminous compounds, in the same
way that the different carbohydrates are each decomposed by specific
ferments.
Very interesting are the various forms of spirilla met with in dung;
Figs. 24 and 25 show Spirillum volutans in the unstained condition, and
also stained to show the flagellæ. It will be noted that the appearance
is so different that, to an inexperienced observer, they might be
taken for different species. The rôle played by these organisms still
requires investigation.
[Illustration: Fig. 23.--B. Butyricus. (Hueppe.)]
[Illustration: Fig. 24.--Spirillum Volutans. (Kutscher.) Stained to
show Flagellae.]
[Illustration: Fig. 25.--Spirillum Volutans. (Kutscher.) Unstained
Preparation.]
I have pointed out previously the importance of the nutrient medium,
or substratum, in which the bacteria grow, on the species surviving.
In it one can see on a small scale the Darwinian process of natural
selection. There is a great struggle for existence between the
various species, and the circumstances determining the survival of
this or that organism are extremely complicated, and we are yet very
much in the dark as to the action of the various chemical compounds
contained in the puer, so that it is unsafe to neglect even those
which are present in only small amounts. Very minute quantities of
certain bodies, almost too small for detection by chemical means,
are sufficient to cause large differences in the growth of certain
organisms. For instance, Raulin found that the addition of a trace
of zinc to his nutrient liquids increased the crop of the mould
Aspergillus niger more than four times the weight of a crop grown in
the same liquid free from zinc.
If we inoculate a nutrient material with a pure culture of bacteria,
and the medium is not exactly adjusted to the needs of the particular
organism, it will not thrive, and will speedily be overgrown by some
other species obtaining access from the air. This fact very much
discounts the use of pure cultures of bacteria which have been proposed
for bating, although in the case of erodin, where the medium has been
adjusted to suit the organism, considerable success has been attained.
The whole of the enzymes and chemical compounds essential for a perfect
bate, are not present in the dung when it leaves the animal’s body, but
these compounds are produced by the continued action of the intestinal
bacteria and other organisms which obtain access from the air. The
production of the enzymes depends, too, upon the composition of the
nutrient medium, since this exerts a selective influence on the species
of bacteria obtaining access to it. Just as in the spontaneous souring
of milk numerous bacteria have free access to it, yet the lactic
ferment is generally so pure that it may be, and is, used as a pure
culture on a large scale in the manufacture of lactic acid.
Coming to the action of the bacteria on the skin fibres, from the
work of Abt and Stiasny,[88] we may conclude that the substance of
the conjunctive fibres is less profoundly decomposed by bacterial
fermentation than by the action of lime. The latter dissolves about 2
per cent. of skin substance from a fresh skin, whereas a puer acting
normally dissolves about 1 per cent.
[88] Sensibilité de la peau verte, et de la peau après l’échauffe,
les pelains, et les confits, à l’égard de la chaux du sel, et de
l’acide acétique. Georges Abt et Edmund Stiasny, Collegium 1910, p. 1
9.
The nuclein of the skin fibres appears to be all removed by the puer,
since Abt confirms the fact that no nuclei can be seen under the
microscope in a puered skin. The actual solution of the skin substance
is brought about by enzymes of a tryptic character. (See Chapter V.)
While the main lines of the bacteriology of the dung bate are now
pretty well known and understood, it will be seen that much work
still remains to be done as to details, and this principally with
the anaerobic bacteria of the dung, which have been studied by few
investigators.[89] I have suggested[90] that such a research might
well be undertaken by the bacteriological laboratories of our Leather
Industries Schools in Leeds and London.
[89] See Les Anaerobies, Jungano and Distaso (Masson et Cie Paris,
1910).
[90] The Bacteriology of the Leather Industry, J.S.C.I., 1910, p. 666.
*Moulds and Putrefaction.*--In view of the fact that moulds are of
frequent occurrence on dog dung, a brief mention of them is necessary.
So far as our present knowledge goes the researches of Van Tieghem, De
Bary, Rankin, Marshall Ward, V. H. Blackman and others indicate that
their action on the essential bating constituents of the dung is a
destructive one. They grow usually on acid media, and in so doing break
down the acids present into simple inorganic bodies, such as CO_{2} and
water, utilizing the carbon and nitrogen for their own growth. Although
these fungi secrete almost all varieties of enzymes (Bourquelot), yet
we have no evidence that any of the enzymes contained in dog dung are
from this source. In the usual case of dung preserved in pits or casks,
the upper surface only becomes mouldy, since moulds require a free
supply of oxygen. The mycelium penetrates but a very little way into
the body of the dung, and cannot therefore effect any decomposition,
except of the surface layer. The dung exposed to the action of the
mould is generally a bad colour, and is rejected as unsuitable for
puering.
The following species have been noted and classified as growing on dog
dung, though probably not all of them are specific.
1. Pilaira dimidiata (Grove).
2. Mucor caninus (a variety of Mucor mucedo).
3. Circinella simplex (Van Tieghem).
4. Pilobolus crystallinus (also on cow-dung).
Certain myxobacteria are found on dung, among these Chondromyces,
described as long ago as 1857 by Berkeley, and at that time included
among the Hyphomycetes. It was rediscovered in 1892 by Thaxton, and
owing to his researches the whole class of myxomycetes is now generally
considered as a division of Bacteria. Another myxomycete, Polyangium
primigenum (Quehl), forming a red fructification on dog dung, is
figured in the Encyclopædia Britannica, XI. edition, vol. 3, p. 163.
The following abstract gives some account of putrefaction, and may be
of use in conjunction with the account of the bacteriology of the bate
which has been given. Since it was written Dr. G. Abt (see Bibliography
51) has also given a very full description of putrefactive processes
as affecting leather manufacture. The subject is still occupying the
attention of a large number of bacteriologists, and we may expect more
light to be thrown on the whole question during the next few years.
ABSTRACT OF PAPER ON RECENT ADVANCES IN THE BACTERIOLOGY OF
PUTREFACTION. Read before the Nottingham section of the Society of
Chemical Industry, January 24, 1906.[91]
[91] Reprinted from the Journal of the Society of Chemical Industry,
February 15, 1906, No. 3, vol. xxv. The numbers in brackets refer to
the Bibliography, Chapter XI.
To those who have to do with the manufacture of leather, the changes
which take place in the skin from the time it leaves the animal are of
the utmost interest. The most important of these changes is the natural
process of decomposition known as putrefaction.
Putrefaction may be defined as the decomposition of nitrogenous organic
matter by living organisms, accompanied by the evolution of malodorous
gases. The study of it may be divided into two parts--(1) the
biological, (2) the chemical. The first concerns the organisms which
break down the proteid molecule either directly or by means of enzymes;
the second that of the different products of the action of these
organisms. It is extremely difficult to separate these two studies.
Dr. Sims Woodhead (59) gives a concise account of the earliest
researches on the organisms causing putrefaction by Leeuwenhoek (1692),
Plenciz of Vienna, Müller of Copenhagen (1786), Needham (1749),
Spallanzani (1769), Schwann (1837), Schroeder and Van Dusch (1854),
Tyndall (1870), Lister (1878). These names show that the history of
putrefaction proceeds parallel with the evolution of the microscope and
the development of the comparatively recent science of bacteriology. I
propose to-night briefly to carry it up to the present day.
I need scarcely say that putrefaction is not a specific fermentation
like alcoholic or acetic fermentation, but that it is extremely
complex. In any putrefying matter, such as gelatin or albumin, a large
number of different species of bacteria may be observed as well as
monads and infusoria, and in some cases moulds, all of which take
part in the process. The first stage is a process of oxidation in the
presence of air, in which ærobic bacteria use up the oxygen present and
only simple inorganic compounds are formed, carbon dioxide, nitrates
and sulphates; this part of the process is generally without odour.
The second stage, or true putrefaction, takes place in the absence of
oxygen by anærobic bacteria, and is a process of reduction. It has
been shown that there are no bacteria in healthy tissues, and if a
muscle or any organ is taken from an animal under antiseptic conditions
it may be preserved indefinitely in a sterile vessel to which filtered
air has free access. Solid matter is usually liquefied by organisms
like B. liquefaciens magnus, which are invariably present in the air,
and which prepare the way for more specifically putrefactive bacteria,
such as Proteus vulgaris and B. putrificus, but if one observes a
number of putrefactions of the same kind of matter under natural
conditions, scarcely any two follow the same course. The modern study
of putrefaction dates from Hauser (58), who, in 1885, isolated from
putrefying flesh the three organisms--Proteus vulgaris, P. mirabilis,
and P. zenkeri. He studied the action of these in pure cultures, and
came to the following conclusions:--
That Bacterium termo (Ehr.) is not a single definite species; various
forms and stages of other organisms have been described under this
name. The various species of Proteus go through a wide range of forms
during their development in which cocci, short and long rods, thread
forms, vibrios, spirilli, and spirochætæ occur. Under special nutritive
conditions Proteus goes through a swarm stage, in which condition
it is capable of moving over the surface and in the solid gelatin.
The Proteus bacteria are facultatively anærobic, they all cause
putrefaction; P. vulgaris and P. mirabilis are the commonest and most
active of all putrefactive bacteria. They do not secrete an unorganised
ferment, but decompose albuminous bodies by direct action. They also
produce a powerful poison, of which small quantities injected into
animals produce septicæmia.
Tito Carbone (60) found amongst the products of P. vulgaris, choline,
ethylenediamine, gadinine, and trimethylamine. Macé (61), criticising
Hauser’s work, considers the cocci form of Proteus to be spores.
Bienstock (62) believes the rôle of the Proteus group somewhat
doubtful. He discovered (1884) another widely distributed putrefactive
organism, which he called Bacillus putrificus; it is a spore bearing,
drumstick shaped bacillus found in fæces; it is anærobic and specially
attacks fibrin. Now fibrin is extremely resistent to the action of
most putrefactive bacteria, and it is very probable that specific
organisms ferment the different albuminous compounds in the same way
that the different carbohydrates are each decomposed by specific
ferments. A certain number of species of bacteria are able to decompose
both carbohydrates and proteids. Tissier and Martelly (70) call these
mixed ferments, and divide them further into two groups (1), mixed
proteolytic ferments, including B. perfringens, B. bifermentans
sporogenes, Staphylococcus albus, Micrococcus flavus liquefaciens,
Proteus vulgaris, this group decompose albumin by means of tryptic
enzymes. (2) Mixed peptolytic ferments are only able to attack the
albumin when it has undergone a preliminary decomposition. This group
comprises B. coli, B. filiformis, Streptococcus pyogenes, Diplococcus
griseus non liquefaciens.
The second class of bacteria are those which are without action on
carbohydrates, and only attack proteids; these consist of the true
proteolytic bacteria B. putrificus, and B. putidus gracilis, and the
peptolytic bacteria, Diplococcus magnus anaerobius and Proteus zenkeri,
which can only decompose peptones.
These authors state that B. putrificus is always present in putrefying
albumin, but always accompanied by facultative ærobes which favour the
growth and development of the special putrefactive bacteria.
In the putrefaction of meat the reaction is first acid owing to the
action of the mixed ferments on the sugars present. In the next stage
ammonia is formed by the tryptic enzymes secreted by the ærobic
bacteria, and so the anærobic organisms are enabled to develop. We can
thus understand how it is that putrefaction proceeds more rapidly the
more mixed ferments there are present, although these were formerly
supposed to hinder putrefaction from taking place.
When meat is exposed to air it is first attacked by the mixed ferments,
Micrococcus flavus liquefaciens, Staphylococcus, Bacillus coli,
Bacillus filiformis, Streptococcus and Diplococcus, and becomes acid;
at the same time, the presence of decomposition products of albumin
may be detected, proteoses, amidoacids, amines and ammonia; the
latter quickly neutralise the acids, and in three to four days the
meat is alkaline, and has a faint putrid smell. Bacillus perfringens
and Bacillus bifermentans sporogenes now make their appearance; the
latter of these organisms produces amines, amido-acids and ammonia. In
this stage the simple anærobic ferments are able to begin their work,
and real putrefaction sets in; as this proceeds, the mixed ferments
gradually disappear, and finally the only organisms remaining are
Bacillus putrificus, Bacillus putidus gracilis, and Diplococcus griseus
non liquefaciens.
Another organism, which appears to play an important part in the
decomposition of animal bodies, is described by Klein (63); he found
that in bodies, which had been buried from three to six weeks, bacteria
such as B. coli and B. proteus had almost disappeared, and an anærobic
bacterium, which he calls B. cadaveris sporogenes, was very active. It
is a motile bacillus 2–4 µ long, with flagellæ all over its surface.
Spores are formed at the rounded ends, giving it a drumstick form. It
coagulates milk, the clot gradually dissolving. It grows on all the
usual nutritive media, but only under strictly anærobic conditions.
In a paper, entitled “Fermentation in the Leather Industry,”[92] I
gave a short account of the progress of putrefaction as it takes
place in the animal skin, and also described some of the organisms
I had observed in putrefying skin. A small piece of skin was placed
in water and allowed to stand at room temperature. During the first
two days there was little change, but on the third day a number of
swiftly moving darting monads made their appearance. Some of these
were propelled by flagellæ, but a few had assumed amœboid forms. A
slowly moving bacillus consisting of a long straight rod, apparently
broken up into cells exactly like the Vibrio subtilis, illustrated
in the “Micrographic Dictionary,” was observed, accompanied by some
species of spirillum. Higher organisms present were a Paramœcium and a
colourless transparent piece of protoplasm, shaped like a dumb-bell,
with a slow rotating motion. On the fifth day the number of vibrios
and spirilli had greatly increased, some with a swifter motion than
others. There were also many large infusoria present; one of a peculiar
double form, which appeared to be a development of the dumb-bell shaped
piece of protoplasm seen on the third day. On the seventh day the most
striking feature was the great increase in the number of vibrios; the
field of the microscope was crowded; masses of the bacilli could be
seen clustered round small particles of the disintegrating skin as
if feeding upon it; there were more infusoria, many of them short,
boat-shaped monads, with a trembling motion, refracting light strongly;
these evidently accompany the putrefaction bacteria, and assist in the
final disintegration. On the ninth day the piece of skin was entirely
dissolved.
[92] J.S.C.I., 1894, 218.
Procter calls attention to the relative putrescibility of the different
constituents of skin, and especially to the rapid putrescence of the
lymph and serum. So far as I know, this part of the subject has not
been studied at all thoroughly, and there is a considerable field open
to workers in our research laboratories.
Pure fat is not decomposed by bacteria, but if albuminous matter is
present, the fat is split up by several species of bacteria and moulds.
Schreiber (73) has shown that the presence of oxygen is necessary. As
this subject scarcely comes within the category of putrefaction, I
refer you to Schreiber’s paper, and also to an important paper by Otto
Rahn (74) recently published.
In the putrefaction of vegetable matter the cellulose is attacked
by specific organisms, which have been thoroughly investigated by
Omeliansky (75). He has shown that the fermentation of cellulose is
an anærobic process, caused by two species of bacteria belonging to
the class of butyric ferments. Morphologically the organisms closely
resemble one another, but one of them decomposes the cellulose with
evolution of hydrogen, the other with evolution of methane; in both
cases considerable amounts of acetic acid and normal butyric acid are
produced.
I have previously stated that monads and infusoria take part in the
process of putrefaction, but I do not know that their action has
been studied in the same way as that of bacteria. The life history
and morphology of some of these monads was studied in 1871 to 1875
by Dallinger and Drysdale (76). These authors, in their researches
into the life history of the monads found in a putrefying infusion of
cod’s head, came to the conclusion that “bacteria are not the only or
even (in the end) the chief organic agents of putrefaction, for most
certainly in the later stages of a disintegration of dead organic
matter the most active agents are a large variety of flagellate monads.”
Dallinger cultivated some of the monads in Cohn’s fluid, and found
that they lived and multiplied in it. Their spores were killed at a
temperature of 250° F. There is a big field of research open in this
direction.
The consideration of the chemical aspect of putrefaction is a vast
subject, and would demand a special treatise. I shall only call your
attention to one or two points of interest.
Taking the simpler bodies first, sulphuretted hydrogen is formed in
putrefying liquids in two ways: (1) by reduction of the sulphates in
the liquid by an anærobic organism Spirillum desulfuricans; (2) by
bacteria capable of growing in the presence of oxygen such as B. coli
commune and B. lactis ærogenes, which ferment glucoses with formation
of lævorotatory lactic acid and evolution of CO_{2} and hydrogen, and
if at the same time the material contains albumin or sulphur, H_{2}S
is given off; these organisms are incapable of reducing sulphates.
Beijerinck (64) has investigated this process, and found a variety of
different forms intermediate between the two above-mentioned, but all
possessing the same characteristics so far as their chemical action is
concerned, so that they may be classed as one order, which he calls
Aerobacter.
Stich (65) found phosphorus pentoxide in the residue from the
putrefaction of casein, nuclein, lecithin, and protagon; and in the
putrefaction of certain organs of animals and plants, gases containing
phosphorus are evolved. The nucleic acid of yeast yielded phosphoric
acid along with hypoxanthin and xanthin.
Vitali (66) found in the putrefaction of muscle, which had been freed
from sugars and fat, that some alcohol was produced. He considers that
a hexose is split off from the albumin in a similar manner to the
splitting off of a fermentable sugar from the glucoproteids (compounds
of simple proteins with carbohydrates). The formation of alcohol in the
putrefaction of muscle occurs in the alkaline stage. Thus alcoholic
fermentation is caused not alone by saccharomyces, but also by certain
putrefactive bacteria.
Lermer (77) finds that the putrefaction of barley resembles butyric
fermentation. An analysis of the gases given off during the later
stages of the process gave the following result: nitrogen, 58·88;
hydrogen, 37·43; methane, 3·15. In the residue from the putrefaction he
found acetic, butyric and valerianic acids, but not caproic or caprilic
acid. In the normal steeping process employed for barley the gases
given off consisted almost entirely of carbon dioxide and nitrogen.
This observation is interesting to compare with the evolution of
nitrogen in the fermentation of bran shown by Wood and Willcox.[93]
[93] J.S.C.I., 1893, 442.
The action of putrefactive bacteria has been found capable of
transforming hexoses into pentoses. Salkowski and Neuberg (78)
inoculated a solution of _d_-glukuronic acid with putrefying meat, and
showed that it was changed into _l_-xylose with evolution of CO_{2}
according to the following formula:--
COH(CHOH)_{4}COOH = CO_{2} + COH[CHOH]_{3}CH_{2}OH.
This is an interesting fact, especially as, according to Neuberg, the
pentose contained in animal nucleo-proteids is _l_-xylose.
I wish to express my indebtedness to Dr. Alfred Koch’s “Jahresbericht
über Gärungs-organismen” for some of the abstracts.
The following is a list of putrefactive bacteria which have been
studied in pure cultures:--
1. Proteus Vulgaris (Hauser). 2. Proteus mirabilis. 3. Proteus
Zenckeri. 4. Bacillus Oedematis maligni (Kerry, Nencki, Bovet).
5. Bacillus Chauvæi = B. sarcophyematos bovis. 6. B. Liquefaciens
magnus. 7. B. spinosus. 8. B. putrificus (Bienstock). 9. B. pseudo
œdematicus (Liborius). 10. B. enteritidis sporogenes (Klein). 11.
B. tetani. 12. Clostridium fœtidum. 13. B. cadaveris sporogenes
(Klein). 14. Spirillum desulfuricans (Beijerinck). 15. B. coli
commune. 16. B. lactis ærogenes. 17. B. fermentationis cellulosæ.
18. Micrococcus flavus liquefaciens (Flügge). 19. Diplococcus
griseus non liquefaciens (n. sp.). 20. Streptococcus pyogenes. 21.
Staphylococcus pyogenes albus. 22. Bacillus filiformis ærobius
(n. sp.). 23. Diplococcus magnus anærobius (n. sp.). 24. Bacillus
putidus gracilis (n. sp.). 25. B. perfringens (Frankel). 26. B.
bifermentans sporogenes (n. sp.).
Moulds taking part in putrefaction, principally of fruit and vegetable
matter:--
1. Penicillium glaucum. 2. Mucor mucedo. 3. Mucor piriformis
(Fischer, possibly identical with 2). 4. Mucor stolonifer
(Ehrenberg). 5. Botrytis cinerea (Pers). 6. Mucor racemosus
(Fres). 7. Monilia fructigena (Pers). 8. Fusarium putrefaciens
(Osterwalder). 9. Cephalothecium roseum.