MISCELLANEOUS USE OF BACTERIA IN THE ARTS.
The foods upon which bacteria live are in endless variety, almost
every product of animal or vegetable life serving to supply their
needs. Some species appear to require somewhat definite kinds of
food, and have therefore rather narrow conditions of life, but the
majority may live upon a great variety of organic compounds. As
they consume the material which serves them as food they produce
chemical changes therein. These changes are largely of a nature
that the chemist knows as decomposition changes. By this is meant
that the bacteria, seizing hold of ingredients which constitute
their food, break them to pieces chemically. The molecule of the
original food matter is split into simpler molecules, and the food
is thus changed in its chemical nature. As a result, the compounds
which appear in the decomposing solution are commonly simpler than
the original food molecules. Such products are in general called
decomposition products, or sometimes cleavage products. Sometimes,
however, the bacteria have, in addition to their power of pulling
their food to pieces, a further power of building other compounds
out of the fragments, thus building up as well as pulling down.
But, however they do it, bacteria when growing in any food
material have the power of giving rise to numerous products which
did not exist in the food mass before. Because of their
extraordinary powers of reproduction they are capable of producing
these changes very rapidly and can give rise in a short time to
large amounts of the peculiar products of their growth.
It is to these powers of producing chemical changes in their food
that bacteria owe all their importance in the world. Their power
of chemically destroying the food products is in itself of no
little importance, but the products which arise as the result of
this series of chemical changes are of an importance in the world
which we are only just beginning to appreciate. In our attempt to
outline the agency which bacteria play in our industries and in
natural processes as well, we shall notice that they are sometimes
of value simply for their power of producing decomposition; but
their greatest value lies in the fact that they are important
agents because of the products of their life.
We may notice, in the first place, that in the arts there are
several industries which may properly be classed together as
maceration industries, all of which are based upon the
decomposition powers of bacteria. Hardly any animal or vegetable
substance is able to resist their softening influence, and the
artisan relies upon this power in several different directions.
BENEFITS DERIVED FROM POWERS OF DECOMPOSITION.
Linen.--Linen consists of certain woody fibres of the stem of the
flax. The flax stem is not made up entirely of the valuable
fibres, but largely of more brittle wood fibres, which are of no
use. The valuable fibres are, however, closely united with the
wood and with each other in such an intimate fashion that it is
impossible to separate them by any mechanical means. The whole
cellular substance of the stem is bound together by some cementing
materials which hold it in a compact mass, probably a salt of
calcium and pectinic acid. The art of preparing flax is a process
of getting rid of the worthless wood fibres and preserving the
valuable, longer, tougher, and more valuable fibres, which are
then made into linen. But to separate them it is necessary first
to soften the whole tissue. This is always done through the aid of
bacteria. The flax stems, after proper preparation, are exposed to
the action of moisture and heat, which soon develops a rapid
bacterial growth. Sometimes this is done by simply exposing the
flax to the dew and rain and allowing it to lie thus exposed for
some time. By another process the stems are completely immersed in
water and allowed to remain for ten to fourteen days. By a third
process the water in which the flax is immersed is heated from 75
degrees to 90 degrees F., with the addition of certain chemicals,
for some fifty to sixty hours. In all cases the effect is the
same. The moisture and the heat cause a growth of bacteria which
proceeds with more or less rapidity according to the temperature
and other conditions. A putrefactive fermentation is thus set up
which softens the gummy substance holding the fibres together. The
process is known as "retting," and after it is completed the
fibres are easily isolated from each other. A purely mechanical
process now easily separates the valuable fibres from the wood
fibres. The whole process is a typical fermentation. A
disagreeable odour arises from the fermenting flax, and the liquid
after the fermentation is filled with products which make valuable
manure. The process has not been scientifically studied until very
recently. The bacillus which produces the "retting" is known now,
however, and it has been shown that the "retting" is a process of
decomposition of the pectin cement. No method of separating the
linen fibres in the flax from the wood fibres has yet been devised
which dispenses with the aid of bacteria.
Jute and Hemp.--Almost exactly the same use is made of bacterial
action in the manufacture of jute und hemp. The commercial aspect
of the jute industry has grown to be a large one, involving many
millions of dollars. Like linen, jute is a fibre of the inner bark
of a plant, and is mixed in the bark with a mass of other useless
fibrous material. As in the case of linen, a fermentation by
bacteria is depended upon as a means of softening the material so
that the fibres can be disassociated. The process is called
"retting," as in the linen manufacture. The details of the process
are somewhat different. The jute is commonly fermented in tanks of
stagnant water, although sometimes it is allowed to soak in river
water for a sufficient length of time to produce the softening.
After the fermentation is thus started the jute fibre is separated
from the wood, and is of a sufficient flexibility and toughness to
be woven into sacking, carpets, curtains, table covers, and other
coarse cloth.
Practically the same method is used in separating the tough fibres
of the hemp. The hemp plant contains some long flexible fibres
with others of no value, and bacterial fermentation is relied upon
to soften the tissues so that they may be separated.
Cocoanut fibre, a somewhat similar material is obtained from the
husk of the cocoanut by the same means. The unripened husk is
allowed to steep and ferment in water for a long time, six months
or a year being required. By this time the husk has become so
softened that it can be beaten until the fibres separate and can
be removed. They are subsequently made into a number of coarse
articles, especially valuable for their toughness. Door mats,
brushes, ships' fenders, etc., are illustrations of the sort of
articles made from them.
In each of these processes the fermentation must have a tendency
to soften the desired fibres as well as the connecting substance.
Putrefaction attacks all kinds of vegetable tissue, and if this
"retting" continues too long the desired fibre is decidedly
injured by the softening effect of the fermentation. It is quite
probable that, even as commonly carried on, the fermentation has
some slight injurious effect upon the fibre, and that if some
purely mechanical means could be devised for separating the fibre
from the wood it would produce a better material. But such
mechanical means has not been devised, and at present a
putrefactive fermentation appears to be the only practical method
of separating the fibres.
Sponges.--A somewhat similar use is made of bacteria in the
commercial preparation of sponges. The sponge of commerce is
simply the fibrous skeleton of a marine animal. When it is alive
this skeleton is completely filled with the softer parts of the
animal, and to fit the sponge for use this softer organic material
must be got rid of. It is easily accomplished by rotting. The
fresh sponges are allowed to stand in the warm sun and very
rapidly decay. Bacteria make their way into the sponge and
thoroughly decompose the soft tissues. After a short putrefaction
of this sort the softened organic matter can be easily washed out
of the skeleton and leave the clean fibre ready for market.
Leather preparation.--The tanning of leather is a purely chemical
process, and in some processes the whole operation of preparing
the leather is a chemical one. In others, however, especially in
America, bacteria are brought into action at one stage. The dried
hide which comes to the tannery must first have the hair removed
together with the outer skin. The hide for this purpose must be
moistened and softened. In some tanneries this is done by steeping
it in chemicals. In others, however, it is put into water and
slightly heated until fermentation arises. The fermentation
softens it so that the outer skin can be easily removed with a
knife, and the removal of hair is accomplished at the same time.
Bacterial putrefaction in the tannery is thus an assistance in
preparing the skin for the tanning proper. Even in the subsequent
tanning a bacterial fermentation appears to play a part, but
little is yet known in regard to it.
Maceration of skeletons.--The making of skeletons for museums and
anatomical instruction in general is no very great industry, and
yet it is one of importance. In the making of skeletons the
process of maceration is commonly used as an aid. The maceration
consists simply in allowing the skeleton to soak in water for a
day or two after cleaning away the bulk of the muscles. The
putrefaction that arises softens the connective tissues so much
that the bones may be readily cleaned of flesh.
Citric acid.--Bacterial fermentation is employed also in the
ordinary preparation of citric acid. The acid is made chiefly from
the juice of the lemon. The juice is pressed from the fruit and
then allowed to ferment. The fermentation aids in separating a
mucilaginous mass and making it thus possible to obtain the citric
acid in a purer condition. The action is probably similar to the
maceration processes described above, although it has not as yet
been studied by bacteriologists.
BENEFITS DERIVED FROM THE PRODUCTS OF BACTERIAL LIFE.
While bacteria thus play a part in our industries simply from
their power of producing decomposition, it is primarily because of
the products of their action that they are of value. Wherever
bacteria seize hold of organic matter and feed upon it, there are
certain to be developed new chemical compounds, resulting largely
from decomposition, but partly also from constructive processes.
These new compounds are of great variety. Different species of
bacteria do not by any means produce the same compounds even when
growing in and decomposing the same food material. Moreover, the
same species of bacteria may give rise to different products when
growing in different food materials. Some of the compounds
produced by such processes are poisonous, others are harmless.
Some are gaseous, others are liquids. Some have peculiar odours,
as may be recognised from the smell arising from a bit of decaying
meat. Others have peculiar tastes, as may be realized in the gamy
taste of meat which is in the incipient stages of putrefaction. By
purely empirical means mankind has learned methods of encouraging
the development of some of these products, and is to-day making
practical use of this power, possessed by bacteria, of furnishing
desired chemical compounds. Industries involving the investment of
hundreds of millions of dollars are founded upon the products of
bacterial life, and they have a far more important relation to our
everyday life than is commonly imagined. In many cases the artisan
who is dependent upon this action of microscopic life is unaware
of the fact. His processes are those which experience has taught
produce desired results, but, nevertheless, his dependence upon
bacteria is none the less fundamental.
BACTERIA IN THE FERMENTATIVE INDUSTRIES.
We may notice, first, several miscellaneous instances of the
application of bacteria to various fermentative industries where
their aid is of more or less value to man. In some of the examples
to be mentioned the influence of bacteria is profound and
fundamental, while in others it is only incidental. The
fermentative industries of civilization are gigantic in extent,
and have come to be an important factor in modern civilized life.
The large part of the fermentation is based upon the growth of a
class of microscopic plants which we call yeasts. Bacteria and
yeasts are both microscopic plants, and perhaps somewhat closely
related to each other. The botanist finds a difference between
them, based upon their method of multiplication, and therefore
places them in different classes (Fig. 2, page 19). In their
general power of producing chemical changes in their food
products, yeasts agree closely with bacteria, though the kinds of
chemical changes are different. The whole of the great
fermentative industries, in which are invested hundreds of
millions of dollars, is based upon chemical decompositions
produced by microscopic plants. In the great part of commercial
fermentations alcohol is the product desired, and alcohol, though
it is sometimes produced by bacteria, is in commercial quantities
produced only by yeasts. Hence it is that, although the
fermentations produced by bacteria are more common in Nature than
those produced by yeasts and give rise to a much larger number of
decomposition products, still their commercial aspect is decidedly
less important than that of yeasts. Nevertheless, bacteria are not
without their importance in the ordinary fermentative processes.
Although they are of no importance as aids in the common
fermentative processes, they are not infrequently the cause of
much trouble. In the fermentation of malt to produce beer, or
grape juice to produce wine, it is the desire of the brewer and
vintner to have this fermentation produced by pure yeasts, unmixed
with bacteria. If the yeast is pure the fermentation is uniform
and successful. But the brewer and vintner have long known that
the fermentation is frequently interfered with by irregularities.
The troubles which arise have long been known, but the
bacteriologist has finally discovered their cause, and in general
their remedy. The cause of the chief troubles which arise in the
fermentation is the presence of contaminating bacteria among the
yeasts. These bacteria have been more or less carefully studied by
bacteriologists, and their effect upon the beer or wine
determined. Some of them produce acid and render the products
sour; others make them bitter; others, again, produce a slimy
material which makes the wine or beer "ropy." Something like a
score of bacteria species have been found liable to occur in the
fermenting material and destroy the value of the product of both
the wine maker and the beer brewer. The species of bacteria which
infect and injure wine are different from those which infect and
injure beer. They are ever present as possibilities in the great
alcoholic fermentations. They are dangers which must be guarded
against. In former years the troubles from these sources were much
greater than they are at present. Since it has been demonstrated
that the different imperfections in the fermentative process are
due to bacterial impurities, commonly in the yeasts which are used
to produce the fermentation, methods of avoiding them are readily
devised. To-day the vintner has ready command of processes for
avoiding the troubles which arise from bacteria, and the brewer is
always provided with a microscope to show him the presence or
absence of the contaminating bacteria. While, then, the alcoholic
fermentations are not dependent upon bacteria, the proper
management of these fermentations requires a knowledge of their
habits and characters.
There are certain other fermentative processes of more or less
importance in their commercial aspects, which are directly
dependent upon bacterial action, Some of them we should
unhesitatingly look upon as fermentations, while others would
hardly be thought of as belonging to the fermentation industries.
VINEGAR.
The commercial importance of the manufacture of vinegar, though
large, does not, of course, compare in extent with that of the
alcoholic fermentations. Vinegar is a weak solution of acetic
acid, together with various other ingredients which have come from
the materials furnishing the acid. In the manufacture of vinegar,
alcohol is always used as the source of the acetic acid. The
production of acetic acid from alcohol is a simple oxidation. The
equation C2H6O + O2 = C2H4O2 + H2O shows the chemical change that
occurs. This oxidation can be brought about by purely chemical
means. While alcohol will not readily unite with oxygen under
common conditions, if the alcohol is allowed to pass over a bit of
platinum sponge the union readily occurs and acetic acid results.
This method of acetic-acid production is possible experimentally,
but is impracticable on any large scale. In the ordinary
manufacture of vinegar the oxidation is a true fermentation, and
brought about by the growth of bacteria.
In the commercial manufacture of vinegar several different weak
alcoholic solutions are used. The most common of these are
fermented malt, weak wine, cider, and sometimes a weak solution of
spirit to which is added sugar and malt. If these solutions are
allowed to stand for a time in contact with air, they slowly turn
sour by the gradual conversion of the alcohol into acetic acid. At
the close of the process practically all of the alcohol has
disappeared. Ordinarily, however, not all of it has been converted
into acetic acid, for the oxidation does not all stop at this
step. As the oxidation goes on, some of the acid is oxidized into
carbonic dioxide, which is, of course, dissipated at once into the
air, and if the process is allowed to continue unchecked for a
long enough period much of the acetic acid will be lost in this
way.
The oxidation of the alcohol in all commercial production of
vinegar is brought about by the growth of bacteria in the liquid.
When the vinegar production is going on properly, there is formed
on the top of the liquid a dense felted mass known as the "mother
of vinegar." This mass proves to be made of bacteria which have
the power of absorbing oxygen from the air, or, at all events, of
causing the alcohol to unite with oxygen. It was at first thought
that a single species of bacterium was thus the cause of the
oxidation of alcohol, and this was named Mycoderma aceti. But
further study has shown that several have the power, and that even
in the commercial manufacture of vinegar several species play a
part (Fig. 18), although the different species are not yet very
thoroughly studied. Each appears to act best under different
conditions. Some of them act slowly, and others rapidly, the slow-
growing species appearing to produce the larger amount of acid in
the end. After the amount of acetic acid reaches a certain
percentage, the bacteria are unable to produce more, even though
there be alcohol still left unoxidized. A percentage as high as
fourteen per cent, commonly destroys all their power of growth.
The production of the acid is wholly dependent upon the growth of
the bacteria, and the secret of the successful vinegar manufacture
is the skilful manipulation of these bacteria so as to keep them
in the purest condition and to give them the best opportunity for
growth.
One method of vinegar manufacture which is quite rapid is carried
on in a slightly different manner. A tall cylindrical chamber is
filled with wood shavings, and a weak solution of alcohol is
allowed to trickle slowly through it. The liquid after passing
over the shavings comes out after a number of hours well charged
with acetic acid. This process at first sight appears to be a
purely chemical one, and reminds us of the oxidation which occurs
when alcohol is allowed to pass over a platinum sponge. It has
been claimed, indeed, that this is a chemical oxidation in which
bacteria play no part. But this appears to be an error. It is
always found necessary in this method to start the process by
pouring upon the shavings some warm vinegar. Unless in this way
the shavings become charged with the vinegar-holding bacteria the
alcohol will not undergo oxidation during its passage over them,
and after the bacteria thus introduced have grown enough to coat
the shavings thoroughly the acetic-acid production is much more
rapid than at first. If vinegar is allowed to trickle slowly down
a suspended string, so that its bacteria may distribute themselves
through the string, and then alcohol be allowed to trickle over it
in the same way, the oxidation takes place and acetic acid is
formed. From the accumulation of such facts it has come to be
recognised that all processes for the commercial manufacture of
vinegar depend upon the action of bacteria. While the oxidation of
alcohol into acetic acid may take place by purely chemical means,
these processes are not practical on a large scale, and vinegar
manufacturers everywhere depend upon bacteria as their agents in
producing the oxidation. These bacteria, several species in all,
feed upon the nitrogenous matter in the fermenting mass and
produce the desired change in the alcohol.
This vinegar fermentation is subject to certain irregularities,
and the vinegar manufacturers can not always depend upon its
occurring in a satisfactory manner. Just as in brewing, so here,
contaminating bacteria sometimes find their way into the
fermenting mass and interfere with its normal course. In
particular, the flavour of the vinegar is liable to suffer from
such causes. As yet our vinegar manufacturers have not applied to
acetic fermentation the same principle which has been so
successful in brewing--namely, the use, as a starter of the
fermentation, of a pure culture of the proper species of bacteria.
This has been done experimentally and proves to be feasible. In
practice, however, vinegar makers find that simpler methods of
obtaining a starter--by means of which they procure a culture
nearly though not absolutely pure--are perfectly satisfactory. It
is uncertain whether really pure cultures will ever be used in
this industry.
LACTIC ACID.
The manufacture of lactic acid is an industry of less extent than
that of acetic acid, and yet it is one which has some considerable
commercial importance. Lactic acid is used in no large quantity,
although it is of some value as a medicine and in the arts. For
its production we are wholly dependent upon bacteria. It is this
acid which, as we shall see, is produced in the ordinary souring
of milk, and a large number of species of bacteria are capable of
producing the acid from milk sugar. Any sample of sour milk may
therefore always be depended upon to contain plenty of lactic
organisms. In its manufacture for commercial purposes milk is
sometimes used as a source, but more commonly other substances.
Sometimes a mixture of cane sugar and tartaric acid is used. To
start the fermentation the mixture is inoculated with a mass of
sour milk or decaying cheese, or both, such a mixture always
containing lactic organisms. To be sure, it also contains many
other bacteria which have different effects, but the acid
producers are always so abundant and grow so vigorously that the
lactic fermentation occurs in spite of all other bacteria. Here
also there is a possibility of an improvement in the process by
the use of pure cultures of lactic organisms. Up to the present,
however, there has been no application of such methods. The
commercial aspects of the industry are not upon a sufficiently
large scale to call for much in this direction.
At the present time the only method we have for the manufacture of
lactic acid is dependent upon bacteria. Chemical processes for its
manufacture are known, but not employed commercially. There are
several different kinds of lactic acid. They differ from each
other in the relations of the atoms within their molecule, and in
their relation to polarized light, some forms rotating the plane
of polarized light to the right, others to the left, while others
are inactive in this respect. All the types are produced by
fermentation processes, different species of bacteria having
powers of producing the different types.
BUTYRIC ACID.
Butyric acid is another acid for which we are chiefly dependent
upon bacteria. This acid is of no very great importance, and its
manufacture can hardly be called an industry; still it is to a
certain extent made, and is an article of commerce. It is an acid
that can be manufactured by chemical means, but, as in the case of
the last two acids, its commercial manufacture is based upon
bacterial action. Quite a number of species of bacteria can
produce butyric acid, and they produce it from a variety of
different sources. Butyric acid is a common ingredient in old milk
and in butter, and its formation by bacteria was historically one
of the first bacterial fermentations to be clearly understood. It
can be produced also in various sugar and starchy solutions.
Glycerine may also undergo a butyric fermentation. The presence of
this acid is occasionally troublesome, since it is one of the
factors in the rancidity of butter and other similar materials.
INDIGO PREPARATION.
The preparation of indigo from the indigo plant is a fermentative
process brought about by a specific bacterium. The leaves of the
plant are immersed in water in a large vat, and a rapid
fermentation arises. As a result of the fermentation the part of
the plant which is the basis of the indigo is separated from the
leaves and dissolved in the water; and as a second feature of the
fermentation the soluble material is changed in its chemical
nature into indigo proper. As this change occurs the
characteristic blue colour is developed, and the material is
rendered insoluble in water. It therefore makes its appearance as
a blue mass separated from the water, and is then removed as
indigo.
Of the nature of the process we as yet know very little. That it
is a fermentation is certain, and it has been proved that it is
produced by a definite species of bacterium which occurs on the
indigo leaves. If the sterilized leaves are placed in sterile
water no fermentation occurs and no indigo is formed. If, however,
some of the specific bacteria are added to the mass the
fermentation soon begins and the blue colour of the indigo makes
its appearance. It is plain, therefore, that indigo is a product
of bacterial fermentation, and commonly due to a single definite
species of bacterium. Of the details of the formation, however, we
as yet know little, and no practical application of the facts have
yet been made.
BACTERIA IN TOBACCO CURING.
A fermentative process of quite a different nature, but of immense
commercial value, is found in the preparation of tobacco. The
process by which tobacco is prepared is a long and somewhat
complicated one, consisting of a number of different stages. The
tobacco, after being first dried in a careful manner, is
subsequently allowed to absorb moisture from the atmosphere, and
is then placed in large heaps to undergo a further change. This
process appears to be a fermentation, for the temperature of the
mass rises rapidly, and every indication of a fermentative action
is seen. The tobacco in these heaps is changed occasionally, the
heap being thrown down and built up again in such a way that the
portion which was first at the bottom comes to the top, and in
this way all parts of the heap may become equally affected by the
process. After this process the tobacco is sent to the different
manufacturers, who finish the process of curing. The further
treatment it receives varies widely according to the desired
product, whether for smoking or for snuff, etc. In all cases,
however, fermentations play a prominent part. Sometimes the leaves
are directly inoculated with fermenting material. In the
preparation of snuff the details of the process are more
complicated than in the preparation of smoking tobacco. The
tobacco, after being ground and mixed with certain ingredients, is
allowed to undergo a fermentation which lasts for weeks, and
indeed for months. In the different methods of preparing snuff the
fermentations take place in different ways, and sometimes the
tobacco is subjected to two or three different fermentative
actions. The result of the whole is the slow preparation of the
commercial product. It is during the final fermentative processes
that the peculiar colour and flavour of the snuff are developed,
and it is during the fermentation of the leaves of the smoking
tobacco--either the original fermentation or the subsequent ones--
that the special flavours and aromas of tobacco are produced.
It can not be claimed for a moment that these changes by which the
tobacco is cured and finally brought to a marketable condition are
due wholly to bacteria. There is no question that chemical and
physical phenomena play an important part in them. Nevertheless,
from the moment when the tobacco is cut in the fields until the
time it is ready for market the curing is very intimately
associated with bacteria and fermentative organisms in general.
Some of these processes are wholly brought about by bacterial
life; in others the micro-organisms aid the process, though they
perhaps can not be regarded as the sole agents.
At the outset the tobacco producer has to contend with a number of
micro-organisms which may produce diseases in his tobacco. During
the drying process, if the temperature or the amount of moisture
or the access of air is not kept in a proper condition, various
troubles arise and various diseases make their appearance, which
either injure or ruin the value of the product. These appear to be
produced by micro-organisms of different sorts. During the
fermentation which follows the drying the producer has to contend
with micro-organisms that are troublesome to him; for unless the
phenomena are properly regulated the fermentation that occurs
produces effects upon the tobacco which ruin its character. From
the time the tobacco is cut until the final stage in the curing
the persons engaged in preparing it for market must be on a
constant watch to prevent the growth within it of undesirable
organisms. The preparation of tobacco is for this reason a
delicate operation, and one that will be very likely to fail
unless the greatest care is taken. In the several fermentative
processes which occur in the preparation there is no question that
micro-organisms aid the tobacco producer and manufacturer.
Bacteria produce the first fermentation that follows the drying,
and it is these organisms too, in large measure, that give rise to
all the subsequent fermentations, although seemingly in some cases
purely chemical processes materially aid. Now the special quality
of the tobacco is in part dependent upon the peculiar type of
fermentation which occurs in one or another of these fermenting
actions. It is the fermentation that gives rise to the peculiar
flavour and to the aroma of the different grades of tobacco.
Inasmuch as the various flavours which characterize tobacco of
different grades are developed, at least to a large extent, during
the fermentation processes, it is a natural supposition that the
different qualities of the tobacco, so far as concerns flavour,
are due to the different types of fermentation. The number of
species of bacteria which are found upon the tobacco leaves in the
various stages of its preparation is quite large, and from what we
have already learned it is inevitable that the different kinds of
bacteria will produce different results in the fermenting process.
It would seem natural, therefore, to assume that the different
flavours of different grades may not unlikely be due to the fact
that the tobacco in the different cases has been fermented under
the influence of different kinds of bacteria.
Nor is this simply a matter of inference. To a certain extent
experimental evidence has borne out the conclusion, and has given
at least a slight indication of practical results in the future.
Acting upon the suggestion that the difference between the high
grades of tobacco and the poorer grades is due to the character of
the bacteria that produce the fermentation, certain
bacteriologists have attempted to obtain from a high quality of
tobacco the species of bacteria which are infesting it. These
bacteria have then been cultivated by bacteriological methods and
used in experiments for the fermentation of tobacco. If it is true
that the flavour of high grade tobacco is in large measure, or
even in part, due to the action of the peculiar microbes from the
soil where it grows, it ought to be possible to produce similar
flavours in the leaves of tobacco grown in other localities, if
the fermentation of the leaves is carried on by means of the pure
cultures of bacteria obtained from the high grade tobacco. Not
very much has been done or is known in this connection as yet. Two
bacteriologists have experimented independently in fermenting
tobacco leaves by the action of pure cultures of bacteria obtained
from such sources. Each of them reports successful experiments.
Each claims that they have been able to improve the quality of
tobacco by inoculating the leaves with a pure culture of bacteria
obtained from tobacco having high quality in flavour. In addition
to this, several other bacteriologists have carried on experiments
sufficient to indicate that the flavours of the tobacco and the
character of the ripening may be decidedly changed by the use of
different species of micro-organisms in the fermentations that go
on during the curing processes.
In regard to the whole matter, however, we must recognise that as
yet we have very little knowledge. The subject has been under
investigation for only a short time; and, while considerable
information has been derived, this information is not thoroughly
understood, and our knowledge in regard to the matter is as yet in
rather a chaotic condition. It seems certain, however, that the
quality of tobacco is in large measure dependent upon the
character of the fermentations that occur at different stages of
the curing. It seems certain also that these fermentations are
wholly or chiefly produced by microorganisms, and that the
character of the fermentation is in large measure dependent upon
the species of micro-organisms that produce it. If these are
facts, it would seem not improbable that a further study may
produce practical results for this great industry. The study of
yeasts and the methods of keeping yeast from contaminations has
revolutionised the brewing industry. Perhaps in this other
fermentative industry, which is of such great commercial extent,
the use of pure cultures of bacteria may in the future produce as
great revolutions in methods as it has in the industry of the
alcoholic fermentation.
It must not, however, be inferred that the differences in grades
of tobacco grown in different parts of the world are due solely to
variations in the curing processes and to the types of
fermentation. There are differences in the texture of the leaves,
differences in the chemical composition of the tobaccoes, which
are due undoubtedly to the soils and the climatic conditions in
which they grow, and these, of course, will never be affected by
changing the character of the ferment active processes. It is,
however, probable that in so far as the flavours that distinguish
the high and low grades of tobacco are due to the character of the
fermentative processes, they may be in the future, at least to a
large extent, controlled by the use of pure cultures in curing
processes. Seemingly, then, there is as great a future in the
development of this fermentative industry as there has been in the
past in the development of the fermentative industry associated
with brewing and vinting.
OPIUM.
Opium for smoking purposes is commonly allowed to undergo a curing
process which lasts several months. This appears to be somewhat
similar to the curing of tobacco. Apparently it is a fermentation
due to the growth of microorganisms. The organisms in question are
not, however, bacteria in this case, but a species of allied
fungus. The plant is a mould, and it is claimed that inoculation
of the opium with cultures of this mould hastens the curing.
TROUBLESOME FERMENTATIONS.
Before leaving this branch of the subject it is necessary to
notice some of the troublesome fermentations which are ever
interfering with our industries, requiring special methods, or,
indeed, sometimes developing special industries to meet them. As
agents of decomposition, bacteria will of course be a trouble
whenever they get into material which it is desired to preserve.
Since they are abundant everywhere, it is necessary to count upon
their attacking with certainty any fermentable substance which is
exposed to air and water. Hence they are frequently the cause of
much trouble. In the fermentative industries they occasionally
cause an improper sort of fermentation to occur unless care is
taken to prevent undesired species of bacteria from being present.
In vinegar making, improper species of bacteria obtaining access
to the solution give rise to undesirable flavours, greatly
injuring the product. In tobacco curing it is very common for the
wrong species of bacteria to gain access to the tobacco at some
stage of the curing and by their growth give rise to various
troubles. It is the ubiquitous presence of bacteria which makes it
impossible to preserve fruits, meats, or vegetables for any length
of time without special methods. This fact in itself has caused
the development of one of our most important industries. Canning
meats or fruits consists in nothing more than bringing them into a
condition in which they will be preserved from attack of these
micro-organisms. The method is extremely simple in theory. It is
nothing more than heating the material to be preserved to a high
temperature and then sealing it hermetically while it is still
hot. The heat kills all the bacteria which may chance to be lodged
in it, and the hermetical sealing prevents other bacteria from
obtaining access. Inasmuch as all organic decomposition is
produced by bacterial growth, such sterilized and sealed material
will be preserved indefinitely when the operation is performed
carefully enough. The methods of accomplishing this with
sufficient care are somewhat varied in different industries, but
they are all fundamentally the same. It is an interesting fact
that this method of preserving meats was devised in the last
century, before the relation of micro-organisms to fermentation
and putrefaction was really suspected. For a long time it had been
in practical use while scientists were still disputing whether
putrefaction could be avoided by preventing the access of
bacteria. The industry has, however, developed wonderfully within
the last few years, since the principles underlying it have been
understood. This understanding has led to better methods of
destroying bacterial life and to proper sealing, and these have of
course led to greater success in the preservation, until to-day
the canning industries are among those which involve capital
reckoned in the millions.
Occasionally bacteria are of some value in food products. The gamy
flavour of meats is nothing more than incipient decomposition.
Sauer Kraut is a food mass intentionally allowed to ferment and
sour. The value of bacteria in producing butter and cheese
flavours is noticed elsewhere. But commonly our aim must be to
prevent the growth of bacteria in foods. Foods must be dried or
cooked or kept on ice, or some other means adopted for preventing
bacterial growth in them. It is their presence that forces us to
keep our ice box, thus founding the ice business, as well as that
of the manufacture of refrigerators. It is their presence, again,
that forces us to smoke hams, to salt mackerel, to dry fish or
other meats, to keep pork in brine, and to introduce numerous
other details in the methods of food preparation and preservation.