attention which they appeared to me to have deserved. The
fermentation of sugar was generally allowed to be occasioned by the
_Torula cerevisiae_; but it was not admitted that putrefaction was due
to an analogous agency. And yet the two cases present a very striking
parallel. In each a stable chemical compound, sugar in the one case,
albumen in the other, undergoes extraordinary chemical changes under
the influence of an excessively minute quantity of a substance which,
regarded chemically, we should suppose inert. As an example of this
in the case of putrefaction, let us take a circumstance often
witnessed in the treatment of large chronic abscesses. In order to
guard against the access of atmospheric air, we used to draw off the
matter by means of a canula and trocar, such as you see here,
consisting of a silver tube with a sharp-pointed steel rod fitted into
it, and projecting beyond it. The instrument, dipped in oil, was
thrust into the cavity of the abscess, the trocar was withdrawn, and
the pus flowed out through the canula, care being taken by gentle
pressure over the part to prevent the possibility of regurgitation.
The canula was then drawn out with due precaution against the reflux
of air. This method was frequently successful as to its immediate
object, the patient being relieved from the mass of the accumulated
fluid, and experiencing no inconvenience from the operation. But the
pus was pretty certain to reaccumulate in course of time, and it
became necessary again and again to repeat the process. And unhappily
there was no absolute security of immunity from bad consequences.
However carefully the procedure was conducted, it sometimes happened,
even though the puncture seemed healing by first intention, that
feverish symptoms declared themselves in the course of the first or
second day, and, on inspecting the seat of the abscess, the skin was
perhaps seen to be red, implying the presence of some cause of
irritation, while a rapid reaccumulation of the fluid was found to
have occurred. Under these circumstances, it became necessary to open
the abscess by free incision, when a quantity, large in proportion to
the size of the abscess, say, for example, a quart, of pus escaped,
fetid from putrefaction. Now, how had this change been brought about?
Without the germ theory, I venture to say, no rational explanation of
it could have been given. It must have been caused by the
introduction of something from without. Inflammation of the punctured
wound, even supposing it to have occurred, would not explain the
phenomenon. For mere inflammation, whether acute or chronic, though
it occasions the formation of pus, does not induce Putrefaction. The
pus originally evacuated was perfectly sweet, and we know of nothing
to account for the alteration in its quality but the influence of
something derived from the external world. And what could that
something be? The dipping of the instrument in oil, and the
subsequent precautions, prevented the entrance of oxygen. Or even if
you allowed that a few atoms of the gas did enter, it would be an
extraordinary assumption to make that these could in so short a time
effect such changes in so large a mass of albuminous material.
Besides, the pyogenic membrane is abundantly supplied with capillary
vessels, through which arterial blood, rich in oxygen, is perpetually
flowing; and there can be little doubt that the pus, before it was
evacuated at all, was liable to any action which the element might be
disposed to exert upon it.
On the oxygen theory, then, the occurrence of putrefaction under these
circumstances is quite inexplicable. But if you admit the germ
theory, the difficulty vanishes at once. The canula and trocar having
been lying exposed to the air, dust will have been deposited upon
them, and will be present in the angle between the trocar and the
silver tube, and in that protected situation will fail to be wiped off
when the instrument is thrust through the tissues. Then when the
trocar is withdrawn, some portions of this dust will naturally remain
upon the margin of the canula, which is left projecting into the
abscess, and nothing is more likely than that some particles may fail
to be washed off by the stream of out-flowing pus, but may be
dislodged when the tube is taken out, and left behind in the cavity.
The germ theory tells us that these particles of dust will be pretty
sure to contain the germs of putrefactive organisms, and if one such
is left in the albuminous liquid, it will rapidly develop at the high
temperature of the body, and account for all the phenomena.
But striking as is the parallel between putrefaction in this instance
and the vinous fermentation, as regards the greatness of the effect
produced, compared with the minuteness and the inertness, chemically
speaking, of the cause, you will naturally desire further evidence of
the similarity of the two processes. You can see with the microscope
the Torula of fermenting must or beer. Is there, you may ask, any
organism to be detected in the putrefying pus? Yes, gentlemen, there
is. If any drop of the putrid matter is examined with a good glass,
it is found to be teeming with myriads of minute jointed bodies,
called vibrios, which indubitably proclaim their vitality by the
energy of their movements. It is not an affair of probability, but a
fact, that the entire mass of that quart of pus has become peopled
with living organisms as the result of the introduction of the canula
and trocar; for the matter first let out was as free from vibrios as
it was from putrefaction. If this be so, the greatness of the
chemical changes that have taken place in the pus ceases to be
surprising. We know that it is one of the chief peculiarities of
living structures that they possess extraordinary powers of effecting
chemical changes in materials in their vicinity, out of all proportion
to their energy as mere chemical compounds. And we can hardly doubt
that the animalcules which have been developed in the albuminous
liquid, and have grown at its expense, must have altered its
constitution, just as we ourselves alter that of the materials on
which we feed. [Footnote: 'Introductory Lecture before the University
of Edinburgh.']
In the operations of Professor Lister care is taken that every portion
of tissue laid bare by the knife shall be defended from germs; that if
they fall upon the wound they should be killed as they fall. With
this in view he showers upon his exposed surfaces the spray of dilute
carbolic acid, which is particularly deadly to the germs, and he
surrounds the wound in the most careful manner with antiseptic
bandages. To those accustomed to strict experiment it is manifest
that we have a strict experimenter here--a man with a perfectly
distinct object in view, which he pursues with never-tiring patience
and unwavering faith. And the result, in his hospital practice, as
described by himself, has been, that even in the midst of abominations
too shocking to be mentioned here, and in the neighbourhood of wards
where death was rampant from pyaemia, erysipelas, and hospital
gangrene, he was able to keep his patients absolutely free from these
terrible scourges. Let me here recommend to your attention Professor
Lister's 'Introductory Lecture before the University of Edinburgh,'
which I have already quoted; his paper on The Effect of the Antiseptic
System of Treatment on the Salubrity of a Surgical Hospital;' and the
article in the 'British Medical Journal' of January 14, 1871.
If, instead of using carbolic acid spray, he could surround his wounds
with properly filtered air, the result would, he contends, be the
same. In a room where the germs not only float but cling to clothes
and walls, this would be difficult, if not impossible. But surgery is
acquainted with a class of wounds in which the blood is freely mixed
with air that has passed through the lungs, and it is a most
remarkable fact that such air does not produce putrefaction. Professor
Lister, as far as I know, was the first to give a philosophical
interpretation of this fact, which he describes and comments upon
thus:
I have explained to my own mind the remarkable fact that in simple
fracture of the ribs, if the lung be punctured by a fragment, the
blood effused into the pleural cavity, though freely mixed with air,
undergoes no decomposition. The air is sometimes pumped into the
pleural cavity in such abundance that, making its way through the
wound in the pleura costalis, it inflates the cellular tissue of the
whole body. Yet this occasions no alarm to the surgeon (although if
the blood in the pleura were to putrefy, it would infallibly occasion
dangerous suppurative pleurisy). Why air introduced into the pleural
cavity through a wounded lung, should have such wholly different
effects from that entering directly through a wound in the chest, was
to me a complete mystery until I heard of the germ theory of
putrefaction, when it at once occurred to me that it was only natural
that air should be filtered of germs by the air-passages, one of whose
offices is to arrest inhaled particles of dust, and prevent them from
entering the air-cells.
*****
I shall have occasion to refer to this remarkable hypothesis farther
on.
The advocates of the germ theory, both of putrefaction and epidemic
disease, hold that both arise, not from the air, but from something
contained in the air. They hold, moreover, that this 'something' is
not a vapour nor a gas, nor indeed a molecule of any kind, but a
_particle_. [Footnote: As regards size, there is probably no sharp line
of division between molecules and particles; the one gradually shades
into the other. But the distinction that I would draw is this: the
atom or the molecule, if free, is always part of a gas, the particle
is never so. A particle is a bit of liquid or solid matter, formed by
the Aggregation of atoms or molecules.] The term 'particulate 'has
been used in the Reports of the Medical Department of the Privy
Council to describe this supposed constitution of contagious matter;
and Dr. Sanderson's experiments render it in the highest degree
probable, if they do not actually demonstrate, that the virus of
small-pox is 'particulate.' Definite knowledge upon this point is of
exceeding importance, because in the treatment of _particles_ methods
are available which it would be futile to apply to _molecules_.
The Luminous beam as a means of Research.
My own interference with this great question, while sanctioned by
eminent names, has been also an object of varied and ingenious attack.
On this point I will only say that when angry feeling escapes from
behind the intellect, where it may be useful as an urging force, and
places itself athwart the intellect, it is liable to produce all
manner of delusions. Thus my censors, for the most part, have
levelled their remarks against positions which were never assumed, and
against claims which were never made. The simple history of the
matter is this: During the autumn of 1868 I was much occupied with the
observations referred to at the beginning of this discourse, and in
part described in the preceding article. For fifteen years it had
been my habit to make use of floating dust to reveal the paths of
luminous beams through the air; but until 1868 I did not intentionally
reverse the process, and employ a luminous beam to reveal and examine
the dust. In a paper presented to the Royal Society in December, 1869,
the observations which induced me to give more special attention to
the question of spontaneous generation, and the germ theory of
epidemic disease, are thus described:
The Floating Matter of the Air.
Prior to the discovery of the foregoing action (the chemical action of
light upon vapours, Fragment IV.), and also during the experiments
just referred to, the nature of my work compelled me to aim at
obtaining experimental tubes absolutely clean upon the surface, and
absolutely free within from suspended matter. Neither condition is,
however, easily attained.
For however well the tubes might be washed and polished, and however
bright and pure they might appear in ordinary daylight, the electric
beam infallibly revealed signs and tokens of dirt. The air was always
present, and it was sure to deposit some impurity. All chemical
processes, not conducted in a vacuum, are open to this disturbance.
When the experimental tube was exhausted, it exhibited no trace of
floating matter, but on admitting the air through the U-tubes
(containing caustic potash and sulphuric acid), a _dust-cone_ more or
less distinct was always revealed by the powerfully condensed electric
beam.
The floating motes resembled minute particles of liquid which had been
carried mechanically from the U-tubes into the experimental tube.
Precautions were therefore taken to prevent any such transfer. They
produced little or no mitigation. I did not imagine, at the time,
that the dust of the external air could find such free passage through
the caustic potash and sulphuric acid. This, however, was the case;
the motes really came from without. They also passed with freedom
through a variety of aethers and alcohols. In fact, it requires
long-continued action on the part of an acid first to wet the motes
and afterwards to destroy them. By carefully passing the air through
the flame of a spirit lamp, or through a platinum tube heated to
bright redness, the floating matter was sensibly destroyed. It was
therefore combustible, in other words, organic, matter. I tried to
intercept it by a large respirator of cotton-wool. Close pressure was
necessary to render the wool effective. A plug of the wool, rammed
pretty tightly into the tube through which the air passed, was finally
found competent to hold back the motes. They appeared from time to
time afterwards, and gave me much trouble; but they were invariably
traced in the end to some defect in the purifying apparatus--to some
crack or flaw in the sealing-wax employed to render the tubes
air-tight. Thus through proper care, but not without a great deal of
searching out of disturbances, the experimental tube, even when filled
with air or vapour, contains nothing competent to scatter the light.
The space within it has the aspect of an absolute vacuum.
An experimental tube in this condition I call _optically empty_.
The simple apparatus employed in these experiments will be at once
understood by reference to a figure printed in the last article (Fig.
3.) s s' is the glass experimental tube, which has varied in length
from 1 to 5 feet, and which may be from 2 to 3 inches in diameter.
From the end s, the pipe pp' passes to an air-pump. Connected with
the other end s' we have the flask F, containing the liquid whose
vapour is to be examined; then follows a U-tube, T, filled with
fragments of clean glass, wetted with sulphuric acid; then a second
U-tube, T, containing fragments of marble, wetted with caustic potash;
and finally a narrow straight tube t t', containing a tolerably
tightly fitting plug of cotton-wool. To save the air-pump gauge from
the attack of such vapours as act on mercury, as also to facilitate
observation, a separate barometer tube was employed.
Through the cork which stops the flask F two glass tubes, a and b,
pass air-tight. The tube a ends immediately under the cork; the tube
b, on the contrary, descends to the bottom of the flask and dips into
the liquid. The end of the tube b is drawn out so as to render very
small the orifice through which the air escapes into the liquid.
The experimental tube s s' being exhausted, a cock at the end s' is
turned carefully on. The air passes slowly through the cotton-wool,
the caustic potash, and the sulphuric acid in succession. Thus
purified, it enters the flask F and bubbles through the liquid.
Charged with vapour, it finally passes into the experimental tube,
where it is submitted to examination. The electric lamp L placed at
the end of the experimental tube furnishes the necessary beam.
*****
The facts here forced upon my attention had a bearing too evident to
be overlooked. The inability of air which had been filtered through
cotton-wool to generate animalcular life, had been demonstrated by
Schroeder and Pasteur: here the cause of its impotence was rendered
evident to the eye. The experiment proved that no sensible amount of
light was scattered by the molecules of the air; that the scattered
light always arose from suspended particles; and the fact that the
removal of these abolished simultaneously the power of scattering
light and of originating life, obviously detached the life-originating
power from the air, and fixed it on something suspended in the air.
Gases of all kinds passed with freedom through the plug of
cotton-wool; hence the thing whose removal by the cotton-wool rendered
the gas impotent, could not itself have been matter in the gaseous
condition. It at once occurred to me that the retina, protected as it
was, in these experiments, from all extraneous light, might be
converted into a new and powerful instrument of demonstration in
relation to the germ theory.
But the observations also revealed the danger incurred in experiments
of this nature; showing that without an amount of care far beyond that
hitherto bestowed upon them, such experiments left the door open to
errors of the gravest description. It was especially manifest that
the chemical method employed by Schultze in his experiments, and so
often resorted to since, might lead to the most erroneous
consequences; that neither acids nor alkalies had the power of rapid
destruction hitherto ascribed to them. In short, the employment of
the luminous beam rendered evident the cause of success in experiments
rigidly conducted like those of Pasteur; while it made equally evident
the certainty of failure in experiments less severely carried out.
Dr. Bennett's Experiments.
But I do not wish to leave an assertion of this kind without
illustration. Take, then, the well-conceived experiments of Dr.
Hughes Bennett, described before the Royal Society of Surgeons in
Edinburgh on January 17, 1868. [Footnote: 'British Medical Journal,'
13, pt. ii. 1868.] Into flasks containing decoctions of
liquorice-root, hay, or tea, Dr. Bennett, by an ingenious method,
forced air. The air was driven through two U-tubes, the one
containing a solution of caustic potash, the other sulphuric acid.
'All the bent tubes were filled with fragments of pumice-stone to
break up the air, so as to prevent the possibility of any germs
passing through in the centre of bubbles.' The air also passed
through a Liebig's bulb containing sulphuric acid, and also through a
bulb containing gun-cotton.
It was only natural for Dr. Bennett to believe that his 'bent tubes'
entirely cut off the germs. Previous to the observations just
referred to, I also believed in their efficacy. But these
observations destroy any such notion. The gun-cotton, moreover, will
fail to arrest the whole of the floating matter, unless it is tightly
packed, and there is no indication in Dr. Bennett's memoir that it was
so packed. On the whole, I should infer, from the mere inspection of
Dr. Bennett's apparatus, the very results which he has described--a
retardation of the development of life, a total absence of it in some
cases, and its presence in others.
In his first series of experiments, eight flasks were fed with sifted
air, and five with common air. In ten or twelve days all the five had
fungi in them; whilst it required from four to nine months to develop
fungi in the others. In one of the eight, moreover, even after this
interval no fungi appeared. In a second series of experiments there
was a similar exception. In a third series the cork stoppers used in
the first and second series were abandoned, and glass stoppers
employed. Flasks containing decoctions of tea, beef, and hay were
filled with common air, and other flasks with sifted air. In every
one of the former fungi appeared and in not one of the latter. These
experiments simply ruin the doctrine that Dr. Bennett finally
espouses.
In all these negative cases, the prepared air was forced into the
infusion when it was boiling hot. Dr. Bennett made a fourth series of
experiments, in which, previous to forcing in the air, he permitted
the flasks to cool. Into four bottles thus treated he forced prepared
air, and after a time found fungi in all of them. What is his
conclusion? Not that the boiling hot liquid, employed in his first
experiments, had destroyed such germs as had run the gauntlet of his
apparatus; but that air which, previous to being sealed up, had been
exposed to a temperature of 212°, _is too rare to support life_. This
conclusion is so remarkable that it ought to be stated in Dr.
Bennett's own words. 'It may be easily conceived that air subjected
to a boiling temperature is so expanded as scarcely to merit the name
of air, and that it is more or less unfit for the purpose of
sustaining animal or vegetable life.'
Now numerical data are attainable here, and as a matter of fact I live
and flourish for a considerable portion of each year in a medium of
less density than that which Dr. Bennett describes as scarcely
meriting the name of air. The inhabitants of the higher Alpine
chalets, with their flocks and herds, and the grasses which support
these, do the same; while the chamois rears its kids in air rarer
still. Insect life, moreover, is sometimes exhibited with monstrous
prodigality at Alpine heights.
In a fifth series of experiments sixteen bottles were filled with
infusions. Into four of them, while cold, ordinary unheated and
unsifted air was pumped. In these four bottles fungi were developed.
Into four other bottles, containing a boiling infusion, ordinary air
was also pumped--no fungi were here developed. Into four other
bottles containing an infusion which had been boiled and permitted to
cool, sifted air was pumped--no fungi were developed. Finally, into
four bottles containing a boiling infusion sifted air was pumped no
fungi were developed. Only, therefore, in the four cases where the
infusions were cold infusions, and the air ordinary air, did fungi
appear.
Dr. Bennett does not draw from his experiments the conclusion to which
they so obviously point. On them, on the contrary, he founds a
defence of the doctrine of spontaneous generation, and a general
theory of spontaneous development. So strongly was he impressed with
the idea that the germs could not possibly pass through his potash and
sulphuric acid tubes, that the appearance of fungi, even in a small
minority of cases, where the air had been sent through these tubes,
was to him conclusive evidence of the spontaneous origin of such
fungi. And he accounts for the absence of life in many of his
experiments by an hypothesis which will not bear a moment's
examination. But, knowing that organic particles may pass unscathed
through alkalies and acids, the results of Dr. Bennett are precisely
what ought wider the circumstances to be expected. Indeed, their
harmony with the conditions now revealed is a proof of the honesty and
accuracy with which they were executed.
The caution exercised by Pasteur both in the execution of his
experiments, and in the reasoning based upon them, is perfectly
evident to those who, through the practice of severe experimental
enquiry, have rendered themselves competent to judge of good
experimental work. He found germs in the mercury used to isolate his
air. He was never sure that they did not cling to the instruments he
employed, or to his own person. Thus when he opened his hermetically
sealed flasks upon the Mer de Glace, he had his eye upon the file used
to detach the drawn-out necks of his bottles; and he was careful to
stand to leeward when each flask was opened. Using these precautions,
he found the glacier air incompetent, in nineteen cases out of twenty,
to generate life; while similar flasks, opened amid the vegetation of
the lowlands, were soon crowded with living things. M. Pouchet
repeated Pasteur's experiments in the Pyrenees, adopting the
precaution of holding his flasks above his head, and obtaining a
different result. Now great care would be needed to render this
procedure a real precaution. The luminous beam at once shows us its
possible effect. Let smoking brown paper be placed at the open mouth
of a glass shade, so that the smoke shall ascend and fill the shade. A
beam sent through the shade forms a bright track through the smoke.
When the closed fist is placed underneath the shade, a vertical wind
of surprising violence, considering the small elevation of
temperature, rises from the band, displacing by comparatively dark air
the illuminated smoke. Unless special care were taken such a wind
would rise from M. Pouchet's body as he held his flasks above his
head, and thus the precaution of Pasteur, of not coming between the
wind and the flask, would be annulled.