Chop up a beefsteak and allow it to remain for two or three hours just
covered with warm water; you thus extract the juice of the beef in a
concentrated form. By properly boiling the liquid and filtering it,
you can obtain from it a perfectly transparent beef-tea. Expose a
number of vessels containing this tea to the moteless air of your
chamber; and expose a number of vessels containing precisely the same
liquid to the dust-laden air. In three days every one of the latter
stinks, and examined with the microscope every one of them is found
swarming with the bacteria of putrefaction. After three months, or
three years, the beef-tea within the chamber is found in every case as
sweet and clear, and as free from bacteria, as it was at the moment
when it was first put in. There is absolutely no difference between
the air within and that without save that the one is dustless and the
other dust-laden.
Clinch the experiment thus: Open the door of your chamber and allow
the dust to enter it. In three days afterwards you have every vessel
within the chamber swarming with bacteria, and in a state of active
putrefaction. Here, also, the inference is quite as certain as in the
case of the powder sown in your garden. Multiply your proofs by
building fifty chambers instead of one, and by employing every
imaginable infusion of wild animals and tame; of flesh, fish, fowl,
and viscera; of vegetables of the most various kinds. If in all these
cases you find the dust infallibly producing its crop of bacteria,
while neither the dustless air nor the nutritive infusion, nor both
together, are ever able to produce this crop, your conclusion is
simply irresistible that the dust of the air contains the germs of the
crop which has appeared in your infusions. I repeat there is no
inference of experimental science more certain than this one. In the
presence of such facts, to use the words of a paper lately published
in the 'Philosophical Transactions,' it would be simply monstrous to
affirm that these swarming crops of bacteria are spontaneously
generated.
Is there then no experimental proof of spontaneous generation? I
answer without hesitation, none! But to doubt the experimental proof
of a fact, and to deny its possibility, are two different things,
though some writers confuse matters by making them synonymous. In
fact, this doctrine of spontaneous generation, in one form or another,
falls in with the theoretic beliefs of some of the foremost workers of
this age; but it is exactly these men who have the penetration to see,
and the honesty to expose, the weakness of the evidence adduced in its
support.
*****
And here observe how these discoveries tally with the common practices
of life. Heat kills the bacteria, colds numbs them. When my
housekeeper has pheasants in charge which she wishes to keep sweet,
but which threaten to give way, she partially cooks the birds, kills
the infant bacteria, and thus postpones the evil day. By boiling her
milk she also extends its period of sweetness. Some weeks ago in the
Alps I made a few experiments on the influence of cold upon ants.
Though the sun was strong, patches of snow still maintained themselves
on the mountain slopes. The ants were found in the warm grass and on
the warm rocks adjacent. Transferred to the snow the rapidity of
their paralysis was surprising. Ina few seconds a vigorous ant, after
a few languid struggles, would wholly lose its power of locomotion and
lie practically dead upon the snow. Transferred to the warm rock, it
would revive, to be again smitten with death-like numbness when
retransferred to the snow. What is true of the ant is specially true
of our bacteria. Their active life is suspended by cold, and with it
their power of producing or continuing putrefaction. This is the
whole philosophy of the preservation of meat by cold. The fishmonger,
for example, when he surrounds his very assailable wares by lumps of
ice, stays the process of putrefaction by reducing to numbness and
inaction the organisms which produce it, and in the absence of which
his fish would remain sweet and sound. It is the astonishing activity
into which these bacteria are pushed by warmth that renders a single
summer's day sometimes so disastrous to the great butchers of London
and Glasgow. The bodies of guides lost in the crevasses of Alpine
glaciers have come to the surface forty years after their interment,
without the flesh showing any sign of putrefaction. But the most
astonishing case of this kind is that of the hairy elephant of Siberia
which was found incased in ice. It had been buried for ages, but when
laid bare its flesh was sweet, and for some time afforded copious
nutriment to the wild beasts which fed upon it.
Beer is assailable by all the organisms here referred to, some of
which produce acetic, some lactic, and some butyric acid, while yeast
is open to attack from the bacteria of putrefaction. In relation to
the particular beverage the brewer wishes to produce, these foreign
ferments have been properly called ferments of disease. The cells of
the true leaven are globules, usually somewhat elongated. The other
organisms are more or less rod-like or eel-like in shape, some of them
being beaded so as to resemble necklaces. Each of these organisms
produces a fermentation and a flavour peculiar to itself. Keep them
out of your beer and it remains for ever unaltered. Never without
them will your beer contract disease. But their germs are in the air,
in the vessels employed in the brewery; even in the yeast used to
impregnate the wort. Consciously or unconsciously, the art of the
brewer is directed against them. His aim is to paralyze, if he cannot
annihilate them.
For beer, moreover, the question of temperature is one of supreme
importance; indeed, the recognised influence of temperature is causing
on the continent of Europe a complete revolution in the manufacture of
beer. When I was a student in Berlin, in 1851, there were certain
places specially devoted to the sale of Bavarian beer, which was then
making its way into public favour. This beer is prepared by what is
called the process of low fermentation; the name being given partly
because the yeast of the beer, instead of rising to the top and
issuing through the bunghole, falls to the bottom of the cask; but
partly, also, because it is produced at a low temperature. The other
and older process, called high fermentation, is far more handy,
expeditious, and cheap. In high fermentation eight days suffice for
the production of the beer; in low fermentation, ten, fifteen, even
twenty days are found necessary. Vast quantities of ice, moreover,
are consumed in the process of low fermentation. In the single
brewery of Dreher, of Vienna, a hundred million pounds of ice are
consumed annually in cooling the wort and beer. Notwithstanding these
obvious and weighty drawbacks, the low fermentation is rapidly
displacing the high upon the Continent. Here are some statistics
which show the number of breweries of both kinds existing in Bohemia
in 1860, 1865, and 1870:
1860. 1865. 1870.
High Fermentation 281 81 18
Low Fermentation 135 459 831
Thus in ten years the number of high-fermentation breweries fell from
281 to 18, while the number of low-fermentation breweries rose from
135 to 831. The sole reason for this vast change--a change which
involves a great expenditure of time, labour, and money--is the
additional command which it gives the brewer over the fortuitous
ferments of disease. These ferments, which, it is to be remembered,
are living organisms, have their activity suspended by temperatures
below 10°C, and as long as they are reduced to torpor the beer remains
untainted either by acidity or putrefaction. The beer of low
fermentation is brewed in winter, and kept in cool cellars; the brewer
being thus enabled to dispose of it at his leisure, instead of forcing
its consumption to avoid the loss involved in its alteration if kept
too long. Hops, it may be remarked, act to some extent as an
antiseptic to beer. The essential oil of the hop is bactericidal:
hence the strong impregnation with hop juice of all beer intended for
exportation.
These low organisms, which one might be disposed to regard as the
beginnings of life, were we not warned that the microscope, precious
and perfect as it is, has no power to show us the real beginnings of
life, are by no means purely useless or purely mischievous in the
economy of nature. They are only noxious when out of their proper
place. They exercise a useful and valuable function as the burners
and consumers of dead matter, animal and vegetable, reducing such
matter, with a rapidity otherwise unattainable, to innocent carbonic
acid and water. Furthermore, they are not all alike, and it is only
restricted classes of them that are really dangerous to man. One
difference in their habits is worthy of special reference here. Air,
or rather the oxygen of the air, which is absolutely necessary to the
support of the bacteria of putrefaction, is, according to Pasteur,
absolutely deadly to the vibrios which provoke the butyric acid
fermentation. This has been illustrated by the following beautiful
observation.
A drop of the liquid containing those small organisms is placed upon
glass, and on the drop is placed a circle of exceedingly thin glass;
for, to magnify them sufficiently, it is necessary that the
object-glass of the microscope should come very close to the
organisms. Round the edge of the circular plate of glass the liquid
is in contact with the air, and incessantly absorbs it, including the
oxygen. Here, if the drop be charged with bacteria, we have a zone of
very lively ones. But through this living zone, greedy of oxygen and
appropriating it, the vivifying gas cannot penetrate to the centre of
the film. In the middle, therefore, the bacteria die, while their
peripheral colleagues continue active. If a bubble of air chance to
be enclosed in the film, round it the bacteria will pirouette and
wabble until its oxygen has been absorbed, after which all their
motions cease. Precisely the reverse of all this occurs with the
vibrios of butyric acid. In their case it is the peripheral organisms
that are first killed, the central ones remaining vigorous while
ringed by a zone of dead. Pasteur, moreover, filled two vessels with
a liquid containing these vibrios; through one vessel be led air, and
killed its vibrios in half an hour; through the other he led carbonic
acid, and after three hours found the vibrios fully active. It was
while observing these differences of deportment fifteen years ago that
the thought of life without air, and its bearing upon the theory of
fermentation, flashed upon the mind of this admirable investigator.
*****
We now approach an aspect of this question which concerns us still
more closely, and will be best illustrated by an actual fact. A few
years ago I was bathing in an Alpine stream, and returning to my
clothes from the cascade which had been my shower-bath, I slipped upon
a block of granite, the sharp crystals of which stamped themselves
into my naked shin. The wound was an awkward one, but being in
vigorous health at the time, I hoped for a speedy recovery. Dipping a
clean pocket-handkerchief into the stream, I wrapped it round the
wound, limped home, and remained for four or five days quietly in bed.
There was no pain, and at the end of this time I thought myself quite
fit to quit my room. The wound, when uncovered, was found perfectly
clean, uninflamed, and entirely free from matter. Placing over it a
bit of goldbeater's-skin, I walked about all day. Towards evening
itching and heat were felt; a large accumulation of matter followed,
and I was forced to go to bed again. The water-bandage was restored,
but it was powerless to check the action now set up; arnica was
applied, but it made matters worse. The inflammation increased
alarmingly, until finally I had to be carried on men's shoulders down
the mountain and transported to Geneva, where, thanks to the kindness
of friends, I was immediately placed in the best medical hands. On
the morning after my arrival in Geneva, Dr. Gautier discovered an
abscess in my instep, at a distance of five inches from the wound. The
two were connected by a channel, or sinus, as it is technically
called, through which he was able to empty the abscess, without the
application of the lance.
By what agency was that channel formed--what was it that thus tore
asunder the sound tissue of my instep, and kept me for six weeks a
prisoner in bed? In the very room where the water dressing had been
removed from my wound and the goldbeater's-skin applied to it, I
opened this year a number of tubes, containing perfectly clear and
sweet infusions of fish, flesh, and vegetable. These hermetically
sealed infusions had been exposed for weeks, both to the sun of the
Alps and to the warmth of a kitchen, without showing the slightest
turbidity or sign of life. But two days after they were opened the
greater number of them swarmed with the bacteria of putrefaction, the
germs of which had been contracted from the dust-laden air of the
room. And had the matter from my abscess been examined, my memory of
its appearance leads me to infer that it would have been found equally
swarming with these bacteria--that it was their germs which got into
my incautiously opened wound, and that they were the subtile workers
that burrowed down my shin, dug the abscess in my instep, and produced
effects which might easily have proved fatal.
This apparent digression brings us face to face with the labours of a
man who combines the penetration of the true theorist with the skill
and conscientiousness of the true experimenter, and whose practice is
one continued demonstration of the theory that the putrefaction of
wounds is to be averted by the destruction of the germs of bacteria.
Not only from his own reports of his cases, but from the reports of
eminent men who have visited his hospital, and from the opinions
expressed to me by continental surgeons, do I gather that one of the
greatest steps ever made in the art of surgery was the introduction of
the antiseptic system of treatment, introduced by Professor Lister.
The interest of this subject does not slacken as we proceed. We began
with the cherry-cask and beer-vat; we end with the body of man. There
are persons born with the power of interpreting natural facts, as
there are others smitten with everlasting incompetence in regard to
such interpretation. To the former class in an eminent degree
belonged the illustrious philosopher Robert Boyle, whose words in
relation to this subject have in them the forecast of prophecy. 'And
let me add,' writes Boyle in his 'Essay on the Pathological Part of
Physic,' 'that he that thoroughly understands the nature of ferments
and fermentations shall probably be much better able than he that
ignores them, to give a fair account of divers phenomena of several
diseases (as well fevers as others), which will perhaps be never
properly understood without an insight into the doctrine of
fermentations.'
Two hundred years have passed since these pregnant words were written,
and it is only in this our day that men are beginning to fully realise
their truth. In the domain of surgery the justice of Boyle's surmise
has been most strictly demonstrated. But we now pass the bounds of
surgery proper, and enter the domain of epidemic disease, including
those fevers so sagaciously referred to by Boyle. The most striking
analogy between a _contagium_ and a ferment is to be found in the power
of indefinite self-multiplication possessed and exercised by both. You
know the exquisitely truthful figures regarding leaven employed in the
New Testament. A particle hid in three measures of meal leavens it
all. A little leaven leaveneth the whole lump. In a similar manner,
a particle of _contagium_ spreads through the human body and may be so
multiplied as to strike down whole populations. Consider the effect
produced upon the system by a microscopic quantity of the virus of
smallpox. That virus is, to all intents and purposes, a seed. It is
sown as yeast is sown, it grows and multiplies as yeast grows and
multiplies, and it always reproduces itself. To Pasteur we are
indebted for a series of masterly researches, wherein he exposes the
looseness and general baselessness of prevalent notions regarding the
transmutation of one ferment into another. He guards himself against
saying it is impossible. The true investigator is sparing in the use
of this word, though the use of it is unsparingly ascribed to him;
but, as a matter of fact, Pasteur has never, been able to effect the
alleged transmutation, while he has been always able to point out the
open doorways through which the affirmers of such transmutations had
allowed error to march in upon them. [Footnote: 'Those who wish for an
illustration of the care necessary in these researches, and of the
carelessness with which they have in some cases been conducted, will
do well to consult the Rev. W. H. Dallinger's excellent 'Notes on
Heterogenesis' in the October number of the Popular Science Review.]
The great source of error here has been already alluded to in this
discourse. The observers worked in an atmosphere charged with the
germs of different organisms; the mere accident of first possession
rendering now one organism, now another, triumphant. In different
stages, moreover, of its fermentative or putrefactive changes, the
same infusion may so alter as to be successively taken possession of
by different organisms. Such cases have been adduced to show that the
earlier organisms must have been transformed into the later ones,
whereas they are simply cases in which different germs, because of
changes in the infusion, render themselves valid at different times.
By teaching us how to cultivate each ferment in its purity--in other
words, by teaching us how to rear the individual organism apart from
all others,--Pasteur has enabled us to avoid all these errors. And
where this isolation of a particular organism has been duly effected
it grows and multiplies indefinitely, but no change of it into another
organism is ever observed. In Pasteur's researches the Bacterium
remained a Bacterium, the Vibrio a Vibrio, the Penicillium a
Penicillium, and the Torula a Torula. Sow any of these in a state of
purity in an appropriate liquid; you get it, and it alone, in the
subsequent crop. In like manner, sow small-pox in the human body,
your crop is small-pox. Sow there scarlatina, and your crop is
scarlatina. Sow typhoid virus, your crop is typhoid--cholera, your
crop is cholera. The disease bears as constant a relation to its
_contagium_ as the microscopic organisms just enumerated do to their
germs, or indeed as a thistle does to its seed. No wonder then, with
analogies so obvious and so striking, that the conviction is spreading
and growing daily in strength, that reproductive parasitic life is at
the root of epidemic disease--that living ferments finding lodgment in
the body increase there and multiply, directly ruining the tissue on
which they subsist, or destroying life indirectly by the generation of
poisonous compounds within the body. This conclusion, which comes to
us with a presumption almost amounting to demonstration, is clinched
by the fact that virulently infective diseases have been discovered
with which living organisms are as closely and as indissolubly
associated as the growth of Torula is with the fermentation of beer.
And here, if you will permit me, I would utter a word of warning to
well-meaning people. We have now reached a phase of this question
when it is of the very last importance that light should once for all
be thrown upon the manner in which contagious and infectious diseases
take root and spread. To this end the action of various ferments upon
the organs and tissues of the living body must be studied; the habitat
of each special organism concerned in the production of each specific
disease must be determined, and the mode by which its germs are spread
abroad as sources of further infection. It is only by such rigidly
accurate enquiries that we can obtain final and complete mastery over
these destroyers. Hence, while abhorring cruelty of all kinds, while
shrinking sympathetically from all animal suffering--suffering which
my own pursuits never call upon me to inflict,--an unbiassed survey of
the field of research now opening out before the physiologist causes
me to conclude, that no greater calamity could befall the human race
than the stoppage of experimental enquiry in this direction. A lady
whose philanthropy has rendered her illustrious said to me some time
ago, that science was becoming immoral; that the researches of the
past, unlike those of the present, were carried on without cruelty. I
replied to her that the science of Kepler and Newton, to which she
referred, dealt with the laws and phenomena of inorganic nature; but
that one great advance made by modern science was in the direction of
biology, or the science of life; and that in this new direction
scientific enquiry, though at the outset pursued at the cost of some
temporary suffering, would in the end prove a thousand times more
beneficent than it had ever hitherto been. I said this because I saw
that the very researches which the lady deprecated were leading us to
such a knowledge of epidemic diseases as will enable us finally to
sweep these scourges of the human race from the face of the earth.
This is a point of such capital importance that I should like to bring
it home to your intelligence by a single trustworthy illustration. In
1850, two distinguished French observers, MM. Davainne and Rayer,
noticed in the blood, of animals which had died of the virulent
disease called splenic fever, small microscopic organisms resembling
transparent rods, but neither of them at that time attached any
significance to the observation. In 1861, Pasteur published a memoir
on the fermentation of butyric acid, wherein he described the organism
which provoked it; and after reading this memoir it occurred to
Davainne that splenic fever might be a case of fermentation set up
within the animal body, by the organisms which had been observed by
him and Rayer. This idea has been placed beyond all doubt by
subsequent research.
Observations of the highest importance have also been made on splenic
fever by Pollender and Brauell. Two years ago, Dr. Burdon Sanderson
gave us a very clear account of what was known up to that time of this
disorder. With regard to the permanence of the _contagium_, it had been
proved to hang for years about localities where it had once prevailed;
and this seemed to show that the rod-like organisms could not
constitute the _contagium_, because their infective power was found to
vanish in a few weeks. But other facts established an intimate
connection between the organisms and the disease, so that a review of
all the facts caused Dr. Sanderson to conclude that the _contagium_
existed in two distinct forms: the one 'fugitive' and visible as
transparent rods; the other permanent but 'latent,' and not yet
brought within the grasp of the microscope.