imagination is drawn upon, not the objective truth of Nature. Such
words sound like the words of knowledge where knowledge is really nil.
The possibility of a 'thin covering' is conceded by those who speak in
this way. Such a covering may, however, exercise a powerful
protective influence. A thin pellicle of India-rubber, for example,
surrounding a pea keeps it hard in boiling water for a time sufficient
to reduce an uncovered pea to a pulp. The pellicle prevents
imbibition, diffusion, and the consequent disintegration. A greasy or
oily surface, or even the layer of air which clings to certain bodies,
would act to some extent in a similar way. 'The singular resistance
of green vegetables to sterilisation,' says Dr. William Roberts,
'appears to be due to some peculiarity of the surface, perhaps their
smooth glistening epidermis which prevented complete wetting of their
surfaces.' I pointed out in 1876 that the process by which an
atmospheric germ is wetted would be an interesting subject of
investigation. A dry microscope covering-glass may be caused to float
on water for a year. A sewing-needle may be similarly kept floating,
though its specific gravity is nearly eight times that of water.
Were it not for some specific relation between the matter of the germ
and that of the liquid into which it falls, wetting would be simply
impossible. Antecedent, to all development there must be an
interchange of matter between the germ and its environment; and this
interchange must obviously depend upon the relation of the germ to its
encompassing liquid. Anything that hinders this interchange retards
the destruction of the germ in boiling water. In my paper published
in the 'Philosophical Transactions' for 1877, I add the following
remark:
It is not difficult to see that the surface of a seed or germ may be
so affected by desiccation and other causes as practically to prevent
contact between it and the surrounding liquid. The body of a germ,
moreover, may be so indurated by time and dryness as to resist
powerfully the insinuation of water between its constituent molecules.
It would be difficult to cause such a germ to imbibe the moisture
necessary to produce the swelling and softening which precede its
destruction in a liquid of high temperature.
*****
However this may be--whatever be the state of the surface, or of the
body, of the spores of Bacillus subtilis, they do as a matter of
certainty resist, under some circumstances, exposure for hours to the
heat of boiling water. No theoretic scepticism can successfully stand
in the way of this fact, established as it has been by hundreds, if
not thousands, of rigidly conducted experiments.
*****
We have now to test one of the principal foundations of the doctrine
of spontaneous generation as formulated in this country. With this
view, I place before my friend and co-enquirer two liquids which have
been kept for six months in one of our sealed chambers, exposed to
optically pure air. The one is a mineral solution containing in proper
proportions all the substances which enter into the composition of
bacteria, the other is an infusion of turnip-it might be any one of a
hundred other infusions, animal or vegetable. Both liquids are as
clear as distilled water, and there is no trace of life in either of
them. They are, in fact, completely sterilised. A mutton-chop, over
which a little water has been poured to keep its juices from drying
up, has lain for three days upon a plate in our warm room. It smells
offensively. Placing a drop of the fetid mutton-juice under a
microscope, it is found swarming with the bacteria of putrefaction.
With a speck of the swarming liquid I inoculate the clear mineral
solution and the clear turnip infusion, as a surgeon might inoculate
an infant with vaccine lymph. In four-and-twenty hours the transparent
liquids have become turbid throughout, and instead of being barren as
at first they are teeming with life. The experiment may be repeated a
thousand times with the same invariable result. To the naked eye the
liquids at the beginning were alike, being both equally transparent-to
the naked eye they are alike at the end, being both equally muddy.
Instead of putrid mutton-juice, we might take as a source of infection
any one of a hundred other putrid liquids, animal or vegetable. So
long as the liquid contains living bacteria a speck of it communicated
either to the clear mineral solution, or to the clear turnip infusion,
produces in twenty-four hours the effect here described.
We now vary the experiment thus: Opening the back-door of another
closed chamber which has contained for months the pure mineral
solution and the pure turnip infusion side by side, I drop into each
of them a small pinch of laboratory dust. The effect here is tardier
than when the speck of putrid liquid was employed. In three days,
however, after its infection with the dust, the turnip infusion is
muddy, and swarming as before with bacteria. But what about the
mineral solution which, in our first experiment, behaved in a manner
undistinguishable from the turnip-juice? At the end of three days
there is not a bacterium to be found in it. At the end of three weeks
it is equally innocent of bacterial life. We may repeat the experiment
with the solution and the infusion a hundred times with the same
invariable result. Always in the case of the latter the sowing, of the
atmospheric dust yields a crop of bacteria-never in the former does
the dry germinal matter kindle into active life. [Footnote: This is
the deportment of the mineral solution as described by others. My own
experiments would lead me to say that the development of the
bacteria, though exceedingly slow and difficult, is not impossible.]
What is the inference which the reflecting mind must draw from this
experiment? Is it not as clear as day that while both liquids are
able to feed the bacteria and to enable them to increase and multiply,
after they have been once, fully developed, only one of the liquids is
able to develope into active bacteria the germinal dust of the air?
I invite my friend to reflect upon this conclusion he will, I think,
see that there is no escape from it. He may, if he prefers, hold the
opinion, which I consider erroneous, that bacteria exist in the air,
not as germs but as desiccated organisms. The inference remains, that
while the one liquid is able to force the passage from the inactive to
the active state, the other is not.
But this is not at all the inference which has been drawn from
experiments with the mineral solution.
Seeing its ability to nourish bacteria when once inoculated with the
living active organism, and observing that no bacteria appeared in the
solution after long exposure to the air, the inference was drawn that
neither bacteria nor their germs existed in the air. Throughout
Germany the ablest literature of the subject, even that opposed to
heterogeny, is infected with this error; while heterogenists at home
and abroad have based upon it a triumphant demonstration of, their
doctrine. It is proved, they say, by the deportment of the mineral
solution that neither bacteria nor their germs exist in the air;
hence, if, on exposing a thoroughly sterilised turnip infusion to the
air, bacteria appear, they must of necessity have been spontaneously
generated. In the words of Dr. Bastian: 'We can only infer that whilst
the boiled saline solution is quite incapable of engendering bacteria,
such organisms are able to arise _de novo_ in the boiled organic
infusion.' [Footnote: 'Proceedings of the Royal Society,' vol. xxi. p.
130.]
I would ask my eminent colleague what he thinks of this reasoning now?
The datum is--'A mineral solution exposed to common air does not
develope bacteria;' the inference is--'Therefore if a turnip infusion
similarly exposed develope bacteria, they must be spontaneously
generated.' The inference, on the face of it, is an unwarranted one.
But while as matter of logic it is inconclusive, as matter of fact it
is chimerical. London air is as surely charged with the germs of
bacteria as London chimneys are with smoke. The inference just
referred to is completely disposed of by the simple question: 'Why,
when your sterilised organic infusion is exposed to optically puree
air, should this generation of life _de novo_ utterly cease? Why should
I be able to preserve my turnip-juice side by side with your saline
solution for the three hundred and sixty-five days of the year, in
free connection with the general atmosphere, on the sole condition
that the portion of that atmosphere in contact with the juice shall be
visibly free from floating dust, while three days' exposure to that
dust fills it with bacteria?' Am I over sanguine in hoping that as
regards the argument here set forth he who runs may read, and he who
reads may understand?
We now proceed to the calm and thorough consideration of another
subject, more important if possible than the foregoing one, but like
it somewhat difficult to seize by reason of the very opulence of the
phraseology, logical and rhetorical, in which it has been set forth.
The subject now to be considered relates to what has been called 'the
death-point of bacteria.' Those who happen to be acquainted with the
modern English literature of the question will remember how challenge
after challenge has been issued to panspermatists in general, and to
one or two home workers in particular, to come to close quarters on
this cardinal point. It is obviously the stronghold of the English
heterogenist. 'Water,' he says, `is boiling merrily over a fire when
some luckless person upsets the vessel so that the heated fluid
exercises its scathing influence upon an uncovered portion of the
body-hand, arm, or face. Here, at all events, there is no room for
doubt. Boiling water unquestionably exercises a most pernicious and
rapidly destructive effect upon the living matter of which we are
composed.' [Footnote: Bastian, 'Evolution,' p. 133.] And lest it
should be supposed that it is the high organisation which, in this
case, renders the body susceptible to heat, he refers to the action of
boiling water on the hen's egg to dissipate the notion. 'The
conclusion,' he says, 'would seem to force itself upon us that there
is something intrinsically deleterious in the action of boiling water
upon living matter-whether this matter be of high or of low
organisation.' [Footnote: Bastian, 'Evolution,' p. 135.] Again, at
another place: 'It has been shown that the briefest exposure to the
influence of boiling water is destructive of all living matter.'
[Footnote: Ibid. p. 46]
The experiments already recorded plainly show that there is a marked
difference between the dry bacterial matter of the air, and the wet,
soft, and active bacteria of putrefying organic liquids. The one can
be luxuriantly bred in the saline solution, the others refuse to be
born there, while both of them are copiously developed in a sterilised
turnip infusion. Inferences, as we have already seen, founded on the
deportment of the one liquid cannot with the warrant of scientific
logic be extended to the other. But this is exactly what the
heterogenist has done, thus repeating as regards the death-point of
bacteria the error into which he fell concerning the germs of the air.
Let us boil our muddy mineral solution with its swarming bacteria for
five minutes. In the soft succulent condition in which they exist in
the solution not one of them escapes destruction. The same is true of
the turnip infusion if it be inoculated with the living bacteria
only-the aerial dust being carefully excluded. In both cases the dead
organisms sink to the bottom of the liquid, and without re-inoculation
no fresh organisms will arise. But the case is entirely different when
we inoculate our turnip infusion with the desiccated germinal matter
afloat in the air.
The 'death-point' of bacteria is the maximum temperature at which they
can live, or the minimum temperature at which they cease to live. If,
for example, they survive a temperature of 140°, and do not survive a
temperature of 150°, the death-point lies somewhere between these two
temperatures. Vaccine lymph, for example, is proved by Messrs.
Braidwood and Vacher to be deprived of its power of infection by brief
exposure to a temperature between 140° and 150° Fahr. This may be
regarded as the death-point of the lymph, or rather of the particles
diffused in the lymph, which constitute the real _contagium_. If no
time, however, be named for the application of the heat, the term
'death-point' is a vague one. An infusion, for example, which will
resist five hours' continuous exposure to the boiling temperature,
will succumb to five days' exposure to a temperature 50° Fahr. below
that of boiling. The fully developed soft bacteria of putrefying
liquids are not only killed by five minutes' boiling, but by less than
a single minute's boiling--indeed, they are slain at about the same
temperature as the vaccine. The same is true of the plastic, active
bacteria of the turnip infusion [Footnote: In my paper in the
'Philosophical Transactions' for 1876, I pointed out and illustrated
experimentally the difference, as regards rapidity of development,
between water-germs and air-germs; the growth from the already
softened water-germs proving to be practically as rapid as from
developed bacteria. This preparedness of the germ for rapid
development is associated with its preparedness for rapid
destruction.]
But, instead of choosing a putrefying liquid for inoculation, let us
prepare and employ our inoculating substance in the following simple
way:-Let a small wisp of hay, desiccated by age, be washed in a glass
of water, and let a perfectly sterilised turnip infusion be inoculated
with the washing liquid. After three hours' continuous boiling the
infusion thus infected will often develope luxuriant bacterial life.
Precisely the same occurs if a turnip infusion be prepared in an
atmosphere well charged with desiccated hay-germs. The infusion in
this case infects itself without special inoculation, and its
subsequent resistance to sterilisation is often very great. On the
1st of March last I purposely infected the air of our laboratory with
the germinal dust of a sapless kind of hay mown in 1875. Ten groups
of flasks were charged with turnip infusion prepared in the infected
laboratory, and were afterwards subjected to the boiling temperature
for periods varying from 15 minutes to 240 minutes. Out of the ten
groups only one was sterilised--that, namely, which had been boiled
for four hours. Every flask of the nine groups which had been boiled
for 15, 30, 45, 60, 75, 90, 105, 120, and 180 minutes respectively,
bred organisms afterwards. The same is true of other vegetable
infusions. On the 28th of February last, for example, I boiled six
flasks, containing cucumber infusion prepared in an infected
atmosphere, for periods of 15, 30, 45, 60, 120, and 180 minutes. Every
flask of the group subsequently developed organisms. On the same day,
in the case of three flasks, the boiling was prolonged to 240, 300,
and 360 minutes; and these three flasks were completely sterilised.
Animal infusions, which under ordinary circumstances are rendered
infallibly barren by five minutes' boiling, behave like the vegetable
infusions in an atmosphere infected with hay-germs. On the 30th of
March, for example, five flasks were charged with a clear infusion of
beef and boiled for 60 minutes, 120 minutes, 180 minutes, 240 minutes,
and 300 minutes respectively. Every one of them became subsequently
crowded with organisms, and the same happened to a perfectly pellucid
mutton infusion prepared at the same time. The cases are to be
numbered by hundreds in which similar powers of resistance were
manifested by infusions of the most diverse kinds.
In the presence of such facts I would ask my colleague whether it is
necessary to dwell for a single instant on the one-sidedness of the
evidence which led the conclusion that all living matter has its life
destroyed by 'the briefest exposure to the influence of boiling
water.' An infusion proved to be barren by six months' exposure to
moteless air maintained at a temperature of 90° Fahr, when inoculated
with full-grown active bacteria, fills itself in two days with
organisms so sensitive as to be killed by a few minutes' exposure to a
temperature much below that of boiling water. But the extension of
this result to the desiccated germinal matter of the air is without
warrant or justification. This is obvious without going beyond the
argument itself. But we have gone far beyond the argument, and proved
by multiplied experiment the alleged destruction of all living matter
by the briefest exposure to the influence of boiling water to be a
defusion. The whole logical edifice raised upon this basis falls
therefore to the ground; and the argument that bacteria and their
germs, being destroyed at 140°, must, if they appear after exposure to
212°, be spontaneously generated, is, I trust, silenced for ever.
Through the precautions, variations, and repetitions observed and
executed with the view of rendering its results secure, the separate
vessels employed in this enquiry have mounted up in two years to
nearly ten thousand.
Besides the philosophic interest attaching to the problem of life's
origin, which will be always immense, there are the practical
interests involved in the application of the doctrines here discussed
to surgery and medicine. The antiseptic system, at which I have
already glanced, illustrates the manner in which beneficent results of
the gravest moment follow in the wake of clear theoretic insight.
Surgery was once a noble art; it is now, as well, a noble science.
Prior to the introduction of the antiseptic system, the thoughtful
surgeon could not have failed to learn empirically that there was
something in the air which often defeated the most consummate
operative skill. That something the antiseptic treatment destroys or
renders innocuous. At King's College Mr. Lister operates and dresses
while a fine shower of mixed carbolic acid and water, produced in the
simplest manner, falls upon the wound, the lint and gauze employed in
the subsequent dressing being duly saturated with the antiseptic. At
St. Bartholomew's Mr. Callender employs the dilute carbolic acid
without the spray; but, as regards the real point aimed at--the
preventing of the wound from becoming a nidus for the propagation of
septic bacteria--the practice in both hospitals is the same.
Commending itself as it does to the scientifically trained mind, the
antiseptic system has struck deep root in Germany.
Had space allowed, it would have given me pleasure to point out the
present position of the 'germ theory' in reference to the phenomena of
infectious disease, distinguishing arguments based on analogy--which,
however, are terribly strong--from those based on actual observation.
I should have liked to follow up the account I have already given
[Footnote: 'Fortnightly Review,' November 1876, see article
'Fermentation.'] of the truly excellent researches of a young and an
unknown German physician named Koch, on splenic fever, by an account
of what Pasteur has recently done with reference to the same subject.
Here we have before us a living _contagium_ of the most deadly power,
which we can follow from the beginning to the end of its life cycle.
[Footnote: Dallinger and Drysdale had previously shown what skill and
patience can accomplish, by their admirable observations on the life
history of the monads.] We find it in the blood or spleen of a
smitten animal in the state say of short motionless rods. When these
rods are placed in a nutritive liquid on the warm stage of the
microscope, we soon see them lengthening into filaments which lie, in
some cases, side by side, forming in others graceful loops, or
becoming coiled into knots of a complexity not to be unravelled. We
finally see those filaments resolving themselves into innumerable
spores, each with death potentially housed within it, yet not to be
distinguished microscopically from the harmless germs of Bacillus
subtilis. The bacterium of splenic fever is called Bacillus
Anthracis. This formidable organism was shown to me by M. Pasteur in
Paris last July. His recent investigations regarding the part it
plays pathologically certainly rank amongst the most remarkable
labours of that remarkable man. Observer after observer had strayed
and fallen in this land of pitfalls, a multitude of opposing
conclusions and mutually destructive theories being the result. In
association with a younger physiological colleague, M. Joubert,
Pasteur struck in amidst the chaos, and soon reduced it to harmony.
They proved, among other things, that in cases where previous
observers in France had supposed themselves to be dealing solely with
splenic fever, another equally virulent factor was simultaneously
active. Splenic fever was often overmastered by septicaemia, and
results due solely to the latter had been frequently made the ground
of pathological inferences regarding the character and cause of the
former. Combining duly the two factors, all the previous
irregularities disappeared, every result obtained receiving the
fullest explanation. On studying the account of this masterly
investigation, the words wherewith Pasteur himself feelingly alludes
to the difficulties and dangers of the experimenter's art came home to
me with especial force: 'J'ai tant de fois éprouvé que dans cet art
difficile de l'expérimentation les plus habiles bronchent à chaque
pas, et que l'interprétation des faits nest pas moins périlleuse.'
[Footnote: Comptes-Rendus,' lxxxiii. p. 177.]
********************
XIV SCIENCE AND MAN.
[Footnote: Presidential Address, delivered before the Birmingham and
Midland Institute, October 1877; with additions.]
A MAGNET attracts iron; but when we analyse the effect we learn that
the metal is not only attracted but repelled, the final approach to
the magnet being due to the difference of two unequal and opposing
forces. Social progress is for the most part typified by this duplex
or polar action. As a general rule, every advance is balanced by a
partial retreat, every amelioration is associated more or less with
deterioration. No great mechanical improvement, for example, is
introduced for the benefit of society at large that does not bear
hardly upon individuals. Science, like other things, is subject to
the operation of this polar law, what is good for it under one aspect
being bad for it under another.
Science demands above all things personal concentration. Its home is
the study of the mathematician, the quiet laboratory of the
experimenter, and the cabinet of the meditative observer of nature.
Different atmospheres are required by the man of science, as such, and
the man of action. Thus the facilities of social and international
intercourse, the railway, the telegraph, and the post-office, which
are such undoubted boons to the man of action, react to some extent
injuriously on the man of science. Their tendency is to break up that
concentrativeness which, as I have said, is an absolute necessity to
the scientific investigator.
The men who have most profoundly influenced the world from the
scientific side have habitually sought isolation. Faraday, at a
certain period of his career, formally renounced dining out. Darwin
lives apart from the bustle of the world in his quiet home in Kent.
Mayer and Joule dealt in unobtrusive retirement with the weightiest
scientific questions. There is, however, one motive power in the
world which no man, be he a scientific student or otherwise, can
afford to treat with indifference; and that is, the cultivation of
right relations with his fellow-men--the performance of his duty, not
as an isolated individual, but as a member of society. It is duty in
this aspect, overcoming alike the sense of possible danger and the
desire for repose, that has placed me in your presence here to-night.