eggs of flies. But he did not and he could not know the meaning of
putrefaction itself. He had not the instrumental means to inform him
that it also is a phenomenon attendant on the development of life.
This was first proved in the paper now alluded to. Schwann placed
flesh in a flask filled to one-third of its capacity with water,
sterilised the flask by boiling, and then supplied it for months with
calcined air. Throughout this time there appeared no mould, no
infusoria, no putrefaction; the flesh remained unaltered, while the
liquid continued as clear as it was immediately after boiling. Schwann
then varied his experimental argument, with no alteration in the
result. His final conclusion was, that putrefaction is due to
decompositions of organic matter attendant on the multiplication
therein of minute organisms. These organisms were derived not from
the air, but from something contained in the air, which was destroyed
by a sufficiently high temperature. There never was a more determined
opponent of the doctrine of spontaneous generation than Schwann,
though a strange attempt was made a year and a half ago to enlist him
and others equally opposed to it on the side of the doctrine.
The physical character of the agent which produces putrefaction was
further revealed by Helmholtz in 1843. By means of a membrane, he
separated a sterilised putrescible liquid from a putrefying one. The
sterilised infusion remained perfectly intact. Hence it was not the
liquid of the putrefying mass--for that could freely diffuse through
the membrane--but something contained in the liquid, and which was
stopped by the membrane, that caused the putrefaction. In 1854
Schroeder and von Dusch struck into this enquiry, which was
subsequently followed up by Schroeder alone. These able experimenters
employed plugs of cotton-wool to filter the air supplied to their
infusions. Fed with such air, in the great majority of cases the
putrescible liquids remained perfectly sweet after boiling. Milk
formed a conspicuous exception to the general rule. It putrefied
after boiling, though supplied with carefully filtered air. The
researches of Schroeder bring us up to the year 1859.
In that year a book was published which seemed to overturn some of the
best established facts of previous investigators. Its title was
Hétérogénie, and its author was F. A. Pouchet, Director of the
Museum of Natural History at Rouen. Ardent, laborious, learned, full
not only of scientific but of metaphysical fervour, he threw his whole
energy into the enquiry. Never did a subject require the exercise of
the cold critical faculty more than this one--calm study in the
unravelling of complex phenomena, care in the preparation of
experiments, care in their execution, skilful variation of conditions,
and incessant questioning of results until repetition had placed them
beyond doubt or question. To a man of Pouchet's temperament the
subject was full of danger--danger not lessened by the theoretic bias
with which he approached it. This is revealed by the opening words of
his preface: 'Lorsque, par la meditation, it fut evident pour moi que
la generation spontanée était encore Fun des moyens qu'emploie la
nature pour la reproduction des êtres, je m'appliquai à découvrir par
quell procédés on pouvait parvenir à en mettre les phénomènes en
evidence: It is needless to say that such a prepossession required a
strong curb. Pouchet repeated the experiments of Schulze and Schwann
with results diametrically opposed to theirs. He heaped experiment
upon experiment and argument upon argument, spicing with the sarcasm
of the advocate the logic of the man of science. In view of the
multitudes required to produce the observed results, he ridiculed the
assumption of atmospheric germs. This was one of his strongest
points. 'Si les Proto-organismes que nous voyons pulluler partout et
dans tout, avaient leurs germes dissembles dans l'atmosphère, dans la
proportion mathématiquement indispensable a cet effet, l'air en serait
totalement obscurci, car ill devraient s 'y trouver beaucoup plus
serrés que les globules d'eau qui forment, nos nuages épais. Il n'y a
pas là la moindre exagération.' Recurring to the subject, he
exclaims: 'L'air dans lequel noun vivons aurait presque la densité du
fer.' There is often a virulent contagion in a confident tone, and
this hardihood of argumentative assertion was sure to influence minds
swayed not by knowledge, but by authority. Had Pouchet known that
'the blue ethereal sky' is formed of suspended particles, through
which the sun freely shines, he would hardly have ventured upon this
line of argument.
Pouchet's pursuit of this enquiry strengthened the conviction with
which he began it, and landed him in downright credulity in the end. I
do not question his ability as an observer, but the enquiry needed a
disciplined experimenter. This latter implies not mere ability to
look at things as Nature offers them to our inspection, but to force
her to show herself under conditions prescribed by the experimenter
himself. Here Pouchet lacked the necessary discipline. Yet the
vigour of his onset raised clouds of doubt, which for a time obscured
the whole field of enquiry. So difficult indeed did the subject seem,
and so incapable of definite solution, that when Pasteur made known
his intention to take it up, his friends Biot and Dumas expressed
their regret, earnestly exhorting him to set a definite and rigid
limit to the time he purposed spending in this apparently unprofitable
field. [Footnote: 'Je ne conseillerais à personne,' said Dumas to his
already famous pupil, 'de rester trop longtemps dans ce
sujet.'--Annales de Chimie et de Physique, 1862, vol. lxiv. p. 22.
Since that time the illustrious Perpetual Secretary of the Academy of
Sciences has had good reason to revise this 'counsel.']
Schooled by his education as a chemist, and by special researches on
the closely related question of fermentation, Pasteur took up this
subject under particularly favourable conditions. His work and his
culture had given strength and finish to his natural aptitudes. In
1862, accordingly, he published a paper 'On the Organised Corpuscles
existing in the Atmosphere,' which must for ever remain classical. By
the most ingenious devices he collected the floating particles of the
air surrounding his laboratory in the Rue d'Ulm, and subjected them to
microscopic examination. Many of them he found to be organised
particles. Sowing them in sterilised infusions, he obtained abundant
crops of microscopic organisms. By more refined methods he repeated
and confirmed the experiments of Schwann, which had been contested by
Pouchet, Montegazza, Joly, and Musset. He also confirmed the
experiments of Schroeder and von Dusch. He showed that the cause
which communicated life to his infusions was not uniformly diffused
through the air; that there were aerial interspaces which possessed no
power to generate life. Standing on the Mer de Glace, near the
Montanvert, he snipped off the ends of a number of hermetically sealed
flasks containing organic infusions. One out of twenty of the flasks
thus supplied with glacier air showed signs of life afterwards, while
eight out of twenty of the same infusions, supplied with the air of
the plains, became crowded with life. He took his flasks into the
caves under the Observatory of Paris, and found the still air in these
caves devoid of generative power. These and other experiments,
carried out with a severity perfectly obvious to the instructed
scientific reader, and accompanied by a logic equally severe, restored
the conviction that, even in these lower raches of the scale of being,
life does not appear without the operation of antecedent life.
The main position of Pasteur has been strengthened by practical
researches of the most momentous kind. He has applied the knowledge
won from his enquiries to the preservation of wine and beer, to the
manufacture of vinegar, to the staying of the plague which threatened
utter destruction of the silk husbandry of France, and to the
examination of other formidable diseases which assail the higher
animals, including man. His relation to the improvements which
Professor Lister has introduced into surgery, is shown by a letter
quoted in his Etudes sur la Bière. [Footnote: 1 P. 43.] Professor
Lister there expressly thanks Pasteur for having given him the only
principle which could have conducted the antiseptic system to a
successful issue. The strictures regarding defects of reasoning, to
which we have been lately accustomed, throw abundant light upon their
author, but no shade upon Pasteur.
Redi, as we have seen, proved the maggots of putrefying flesh to be
derived from the eggs of flies; Schwann proved putrefaction itself to
be the concomitant of far lower forms of life than those dealt with by
Redi. Our knowledge here, as elsewhere in connection with this
subject, has been vastly extended by Professor Cohn, of Breslau. 'No
putrefaction,' he says, 'can occur in a nitrogenous substance if its
bacteria be destroyed and new ones prevented from entering it.
Putrefaction begins as soon as bacteria, even in the smallest numbers,
are admitted either accidentally or purposely. It progresses in
direct proportion to the multiplication of the bacteria, it is
retarded when they exhibit low vitality, and is stopped by all
influences which either hinder their development or kill them. All
bactericidal media are therefore antiseptic and disinfecting.'
[Footnote: In his last excellent memoir Cohn expresses himself thus:
'Wer noch heut die Faeulniss von einer spontanen Dissociation der
Proteinmolecule, oder von einem unorganisirten Ferment ableitet, oder
gar aus "Stickstoffsplittern" die Balken zur Stuetze seiner
Faeulnisstheorie zu zimmern versucht, hat zuerst den Satz "keine
Faeulniss ohne Bacterium Termo" zu widerlegen.']
It was these organisms acting in wound and abscess which so frequently
converted our hospitals into charnel-houses, and it is their
destruction by the antiseptic system that now renders justifiable
operations which no surgeon would have attempted a few years ago. The
gain is immense--to the practising surgeon as well as to the patient
practised upon. Contrast the anxiety of never feeling sure whether
the most brilliant operation might not be rendered nugatory by the
access of a few particles of unseen hospital dust, with the comfort
derived from the knowledge that all power of mischief on the part of
such dust has been surely and certainly annihilated. But the action
of living _contagia_ extends beyond the domain of the surgeon. The power
of reproduction and indefinite self-multiplication which is
characteristic of living things, coupled with the undeviating fact of
_contagia_ 'breeding true,' has given strength and consistency to a
belief long entertained by penetrating minds, that epidemic diseases
generally are the concomitants of parasitic life. 'There begins to be
faintly visible to us a vast and destructive laboratory of nature
wherein the diseases which are most fatal to animal life, and the
changes to which dead organic matter passively liable, appear bound
together by what must least be called a very close analogy of
causation.' [Footnote: Report of the Medical Officer of the Privy
Council, 1874, p. 5.] According to this view, which, as I have said,
is daily gaining converts, a contagious disease may be defined a
conflict between the person smitten by it and a specific organism
which multiplies at his expense, appropriating his air and moisture,
disintegrating his tissues, or poisoning him by the decompositions
incident to its growth.
*****
During the ten years extending from 1859 to 1869, researches on
radiant heat in its relations to the gaseous form of matter occupied
my continual attention. When air was experimented on, I had to
cleanse it effectually of floating matter, and while doing so I was
surprised to notice that, at the ordinary rate of transfer, such
matter passed freely through alkalis, acids, alcohols, and ethers. The
eye being kept sensitive by darkness, a concentrated beam of light was
found to be a most searching test for suspended matter both in water
and in air--a test indeed indefinitely more searching and severe than
that furnished by the most powerful microscope. With the aid of such
a beam I examined air filtered by cotton-wool; air long kept free from
agitation, so as to allow the floating matter to subside; calcined
air, and air filtered by the deeper cells of the human lungs. In all
cases the correspondence between my experiments and those of
Schroeder, Pasteur, and Lister in regard to spontaneous generation was
perfect. The air which they found inoperative was proved by the
luminous beam to be optically pure and therefore germless. Having
worked at the subject both by experiment and reflection, on Friday
evening, January 21, 1870, I brought it before the members of the
Royal Institution. Two or three months subsequently, for sufficient
practical reasons, I ventured to direct public attention to the
subject in a letter to the Times. Such was my first contact with this
important question.
This letter, I believe, gave occasion for the first public utterance
of Dr. Bastian in relation to this subject. He did me the honour to
inform me, as others had informed Pasteur, that the subject 'pertains
to the biologist and physician: He expressed 'amazement' at my
reasoning, and warned me that before what I had done could be undone
'much irreparable mischief might be occasioned.' With far less
preliminary experience to guide and warn him, the English heterogenist
was far bolder than Pouchet in his experiments, and far more
adventurous in his conclusions. With organic infusions he obtained
the results of his celebrated predecessor, but he did much more--the
atoms and molecules of inorganic liquids passing under his
manipulation into those more 'complex chemical compounds,' which we
dignify by calling them 'living organisms.' [Footnote: 'It is further
held that bacteria or allied organisms are prone to be engendered as
correlative products, coming into existence in the several
fermentations, just as independently as other less complex chemical
compounds.'--Bastian, Trans. of Pathological Society, vol. xxvi.
258.]
As regards the public who take an interest in such things, and
apparently also as regards a large portion of the medical profession,
our clever countryman succeeded in restoring the subject to a state of
uncertainty similar to that which followed the publication of
Pouchet's volume in 1859.
It is desirable that this uncertainty should be removed from all
minds, and doubly desirable on practical grounds that it should be
removed from the minds of medical men. In the present article,
therefore, I propose discussing this question face to face with some
eminent and fair-minded member of the medical profession who, as
regards spontaneous generation, entertains views adverse to mine. Such
a one it would be easy to name; but it is perhaps better to rest in
the impersonal. I shall therefore simply call my proposed co-enquirer
my friend. With him at my side, I shall endeavour, to the best of my
ability, so to conduct this discussion that he who runs may read and
that he who reads may understand.
Let us begin at the beginning. I ask my friend to step into the
laboratory of the Royal Institution, where I place before him a basin
of thin turnip slices barely covered with distilled water kept a
temperature of 120° Fahr. After digesting the turnip for four or five
hours we pour off the liquid, boil it, filter it, and obtain an
infusion as clear as filtered drinking water. We cool the infusion,
test its specific gravity, and find it to be 1006 or higher--water
being 1000. A number of small clean empty flasks, of the shape shown
on the margin, are before us. One of them is slightly warmed with a
spirit-lamp, and its open end is then dipped into the turnip infusion.
The warmed glass is afterwards chilled, the air within the flasks
cools, contracts, and is followed in its contraction by the infusion.
Thus we get a small quantity of liquid into the flask. We now heat
this liquid carefully. Steam is produced, which issues from the open
neck, carrying the air of the flask along with it. After a few
seconds' ebullition, the open neck is again Plunged into the infusion.
The steam within the flask condenses, the liquid enters to supply its
place, and in this way we fill our little flask to about four-fifths
of its volume. This description is typical; we may thus fill a
thousand flasks with a thousand different infusions.
I now ask my friend to notice a trough made of sheet copper, with two
rows of handy little Bunsen burners underneath it. This trough, or
bath, is nearly filled with oil; a piece of thin plank constitutes a
kind of lid for the oil-bath. The wood is perforated with circular
apertures wide enough to allow our small flask to pass through and
plunge itself in the oil, which has been heated, say, to 250° Fahr.
Clasped all round by the hot liquid, the infusion in the flask rises
to its boiling point, which is not sensibly over 212° Fahr. Steam
issues from the open neck of the flask, and the boiling is continued
for five minutes. With a pair of small brass tongs, an assistant now
seizes the neck near its junction with the flask, and partially lifts
the latter out of the oil. The steam does not cease to issue, but its
violence is abated. With a second pair of tongs held in one hand, the
neck of the flask is seized close to its open end, while with the
other hand a Bunsen's flame or an ordinary spirit flame is brought
under the middle of the neck. The glass reddens, whitens, softens,
and as it is gently drawn out the neck diminishes in diameter, until
the canal is completely blocked up. The tongs with the fragment of
severed neck being withdrawn, the flask, with its contents diminished
by evaporation, is lifted from the oil-bath perfectly sealed
hermetically.
Sixty such flasks filled, boiled, and sealed in the manner described,
and containing strong infusions of beef, mutton, turnip, and cucumber,
are carefully packed in sawdust, and transported to the Alps. Thither,
to an elevation of about 7,000 feet above the sea, I invite my
co-enquirer to accompany me. It is the month of July, and the weather
is favourable to putrefaction. We open our box at the Bel-Alp, and
count out fifty-four flasks, with their liquids as clear as filtered
drinking water. In six flasks, however, the infusion is found muddy.
We closely examine these, and discover that every one of them has had
its fragile end broken off in the transit from London. Air has entered
the flasks, and the observed muddiness is the result. My colleague
knows as well as I do what this means. Examined with a pocket-lens,
or even with a microscope of insufficient power, nothing is seen in
the muddy liquid; but regarded with a magnifying power of a thousand
diameters or so, what an astonishing appearance does it present!
Leeuwenhoek estimated the population of a single drop of stagnant
water at 500,000,000: probably the population of a drop of our turbid
infusion would be this many times multiplied. The field of the
microscope is crowded with organisms, some wabbling slowly, others
shooting rapidly across the microscopic field. They dart hither and
thither like a rain of minute projectiles; they pirouette and spin so
quickly round, that the retention of the retinal impression transforms
the little living rod into a twirling wheel. And yet the most
celebrated naturalists tell us they are vegetables. From the rod-like
shape which they so frequently assume, these organisms are called
'bacteria'--a term, be it here remarked, which covers organisms of
very diverse kinds.
Has this multitudinous life been spontaneously generated in these six
flasks, or is it the progeny of living germinal matter carried into
the flasks by the entering air? If the infusions have a
self-generative power, how are the sterility and consequent clearness
of the fifty-four uninjured flasks to be accounted for? My colleague
may urge--and fairly urge--that the assumption of germinal matter is
by no means necessary; that the air itself may be the one thing needed
to wake up the dormant infusions. We will examine this point
immediately. But meanwhile I would remind him that I am working on
the exact lines laid down by our most conspicuous heterogenist. He
distinctly affirms that the withdrawal of the atmospheric pressure
above the infusion favours the production of organisms; and he
accounts for their absence in tins of preserved meat, fruit, and
vegetables, by the hypothesis that fermentation has begun in such
tins, that gases have been generated, the pressure of which has
stifled the incipient life and stopped its further development.
[Footnote: _Beginnings of Life_, vol. i.] This is the new
theory of preserved meats. Had its author pierced a tin of preserved
meat, fruit, or vegetable under water with the view of testing its
truth, he would have found it erroneous. In well-preserved tins he
would have found, not an outrush of gas, but an inrush of water. I
have noticed this recently in tins which have lain perfectly good for
sixty-three years in the Royal Institution. Modern tins, subjected to
the same test, yielded the same result. From time to time, moreover,
during the last two years, I have placed glass tubes, containing clear
infusions of turnip, hay, beef, and mutton, in iron bottles, and
subjected them to air-pressures varying from ten to twenty-seven
atmospheres--pressures, it is needless to say, far more than
sufficient to tear a preserved meat tin to shreds. After ten days
these infusions were taken from their bottles rotten with putrefaction
and teeming with life. Thus collapses an hypothesis which had no
rational foundation, and which could never have seen the light had the
slightest attempt been made to verify it.
Our fifty-four vacuous and pellucid flasks also declare against the
heterogenist. We expose them to a warm Alpine sun by day, and at night
we suspend them in a warm kitchen. Four of them have been
accidentally broken; but at the end of a month we find the fifty
remaining ones as clear as at the commencement. There is no sign of
putrefaction or of life in any of them. We divide these flasks into
two groups of twenty-three and twenty-seven respectively (an accident
of counting rendered the division uneven). The question now is
whether the admission of air can liberate any generative energy in the
infusions. Our next experiment will answer this question and
something more. We carry the flasks to a hayloft, and there, with a
pair of steel pliers, snip off the sealed ends of the group of
three-and-twenty. Each snipping off is of course followed by an
inrush of air. We now carry our twenty-seven flasks, our pliers, and
a spirit-lamp, to a ledge overlooking the Aletsch glacier, about 200
feet above the hayloft, from which ledge the mountain falls almost
precipitously to the north-east for about a thousand feet. A gentle
wind blows towards us from the north-east--that is, across the crests
and snow-fields of the Oberland mountains. We are therefore bathed by
air which must have been for a good while out of practical contact
with either animal or vegetable life. I stand carefully to leeward of
the flasks, for no dust or particle from my clothes or body must be
blown towards them. An assistant ignites the spirit-lamp, into the
flame of which I plunge the pliers, thereby destroying all attached
germs or organisms. Then I snip off the sealed end of the flask.
Prior to every snipping the same process is gone through, no flask
being opened without the previous cleansing of the pliers by the
flame. In this way we charge our seven-and-twenty flasks with clean
vivifying mountain air.
We place the fifty flasks, with their necks open, over a kitchen
stove, in a temperature varying from 50° to 90° Fahr, and in three
days find twenty-one out of the twenty-three flasks opened on the
hayloft invaded by organisms--two only of the group remaining free
from them. After three weeks' exposure to precisely the same
conditions, not one of the twenty-seven flasks opened in free air had
given way. No germ from the kitchen air had ascended the narrow
necks, the flasks being shaped to produce this result. They are still
in the Alps, as clear, I doubt not, and as free from life as they were
when sent off from London. [Footnote: An actual experiment made at the
Bel Alp is here described.]