LOTJIS PASTEUR

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AND PARLIAMENT STREET

LOUIS PASTEUR

HIS LIFE AND LABOURS

BY HIS SON-IN-LAW

TRANSLATED FROM THE FRENCH

BY

LADY CLAUD HAMILTON

LONDON
LONGMANS, GREEN, AND CO,

1885

All rights reserved

PREFACE.

IN the salon of a distinguished man, or of a great
writer, there is often to be found a person who, without
being either a fellow-worker or a disciple, without
even possessing the scientific or literary qualities which
might explain his habitual presence, lives nevertheless
in complete familiarity with the man whom all around
him call ' dear master.' Whence comes this intimate
one ? who is he ? what is his business ? He is only
known as a friend of the house. He has no other
title, and he is almost proud of having no other.
Stripped of his own personality, he speaks only of the
labours and the success of his illustrious friend, in
the radiance of whose glory he moves with delight.

The author of this work is a person of this descrip-
tion. Intimately connected with the life of M. Pasteur,
and a constant inmate of his laboratory, he has passed
happy years near this great investigator, who has dis-
covered a new world — the world of the infinitely little.
Since the first studies of M. Pasteur on molecular

VI PREFACE.

dissymmetry, down to his most recent investigations
on hydrophobia, on virulent diseases, and on the arti-
ficial cultures of living contagia, which have been
converted by such cultures into veritable vaccines —
passing by the intermediate celebrated experiments on
spontaneous generation, fermentation, the diseases of
wine, the manufacture of beer and vinega-r, and the
diseases of silkworms — the author of these pages has
been able, if not to witness all, at least to follow in
its principal developments this uninterrupted series of
scientific conquests.

' What a beautiful book,' he remarked one day to
M. Pasteur, ' might be written about all this ! '

' But it is all in the Comptes-rendus of the
Academy of Sciences.'

' It is not for the readers of the Comptes-rendus
that such a book needs to be written, but for the great
public, who know that you have done great things,
but who know it only vaguely, by the records of
journals, or by fragments of biography. The persons
are few who know the history of your discoveries.
What was your point of departure ? How have you
arrived at such and such principles, and at the conse-
quences which flow from these principles ? T nat is
the connection and rigorous bond of your method ?
These are the things which it would be interesting to
put together in a book which would have some chance
of enduring as an historic document/

PREFACE. Vll

' I could not waste my time in going back upon
things already accomplished.'

1 No ; but my desire is that someone else should
consecrate his time to the work. And listen,' added
this friend, with audacious frankness — ' do you know
by whom, in my opinion, this book ought to be
written? By a man who, without having been in
any way trained to follow in your footsteps, is ani-
mated by the most lively desire to understand the
course which you have pursued'; who, while living at
your side, has been each day impregnated with your
method and your ideas ; who, having had the happi-
ness of comprehending your life and its achievements,
does not wish to confine the pleasure thus derived to
himself alone.'

' Where, then,' interrupted Pasteur with a kindly
smile, not without a tinge of irony, ' is this man, at
once so happy, and so impatient to share his happi-
ness with others ? '

' He is now pleading his cause before you. Yes,
I would gladly attempt such a work. I have seen
your efforts and observed your success. The experi-
ments which I have not witnessed you have always
freely explained to me, with that gift of clearness
which Vauvenargues called the " polish " of masters.1
Initiated by affection, I would make myself initiator
by admiration. It would be the history of a learned

1 'Vernis des maitres.'

Ill PREFACF.

man by an ignorant one. My ignorance would save
me from dwelling too strictly or too long on technical
details. With the exposition of your doctrine I would
mingle some fragments of your biography. I would
pass from a discovery to an anecdote, and so arrange
matters as to give the book not only the character
of a familiar scientific conversation, which would
hardly be more than the echo of what I have learnt
while near you, but also to make it a reflex of your
life.'

* You should postpone that until I am no longer
here.'

* Why so ? Why, before assigning to them their
places, should we wait till those whose names will en-
dure have disappeared from the scene ? No ; it is you,
living, that I wish to paint — you, in full work, in the
midst of your laboratory. And, in addition to all
other considerations, I would add, that your presence
in the flesh will be the guarantee of my exactitude.'

July 1883.

CONTENTS.

PAGE

INTRODUCTION, BY PROFESSOR TYNDALL .... XI

RECOLLECTIONS OP CHILDHOOD AND YOUTH — FIRST DISCOVERIES 1

FERMENTATION 40

ACETIC FERMENTATION — THE MANUFACTURE OF VINEGAR . 66

THE QUESTION OF SPONTANEOUS GENERATION . . . . 89

STUDIES ON WINE . .' — ~~~7 112

THE SILKWORM-DISEASE 127

DECISIVE EXPERIMENTS .... . . .164

STUDIES ON BEER 168

VIRULENT DISEASES — SPLENIC FEVER, SEPTICAEMIA . . 176

FOWL CHOLERA 212

ATTENUATED VIRUS, OK VACCINATION — THE FOWL CHOLERA

VACCINE 220

THE VACCINE OF SPLENIC FEVER 231

THE RETURN TO VIRULENCE 246

ETIOLOGY OF SPLENIC FEVER 250

METHOD OF DISCUSSION AND CONTRADICTIONS . . .262

THE LABORATORY OF THE ECOLE NORMALE— VARIOUS STUDIES

—HYDROPHOBIA . . . . 271

INTRODUCTION.

IN the early part of the present year the French
original of this work was sent to me from Paris by
its author. It was accompanied by a letter from
M. Pasteur, expressing his desire to have the work
translated and published in England. Eesponding to
this desire, I placed the book in the hands of the
Messrs. Longman, who, in the exercise of their own
judgment, decided on publication. The translation was
confided, at my suggestion, to Lady Claud Hamilton.

The translator's task was not always an easy one,
but it has, I think, been well executed. A few slight
abbreviations, for which I am responsible, have been
introduced, but in no case do they affect the sense.
It was, moreover, found difficult to render into suitable
English the title of the original : ' M. Pasteur, His-
toire d'un Savant par un Ignorant.' A less piquant and
antithetical English title was, therefore, substituted for
the French one.

This filial tribute, for such it is, was written, under
the immediate supervision of M. Pasteur, by his

Xll INTRODUCTION.

devoted and admiring son-in-law, M. Valery Eadot. It
is the record of a life of extraordinary scientific ardour
and success, the picture of a mind on which facts fall
like germs upon a nutritive soil, and, like germs so
favoured, undergo rapid increase and multiplication.
One hardly knows which to admire most- -the in-
1 tuitive vision which discerns in advance the new
'I issues to which existing data point, or the skill in
device, the adaptation of means to ends, whereby the
intuition is brought to the test and ordeal of experi-
ment.

In the investigation of microscopic organisms — the
' infinitely little,' as Pouchet loved to call them — and
their doings in this our world, M. Pasteur has found
his true vocation. In this broad field it has been his
good fortune to alight upon a crowd of connected
Y problems of the highest public and scientific interest,
ripe for solution, and requiring for their successful
treatment the precise culture and capacities which he
has brought to bear upon them. He may regret his
abandonment of molecular physics ; he may look
fondly back upon the hopes with which his researches
on the tartrates and paratartrates inspired him; he
may think that great things awaited him had he
continued to labour in this line. I do not doubt it.
But this does not shake my conviction that he yielded
to the natural affinities of his intellect, that he obeyed
its truest impulses, and reaped its richest rewards, in

.INTRODUCTION. xiii

pursuing the line that he has chosen, and in which
his labours have rendered him one of the most con-
spicuous scientific figures of this age.

With regard to the earliest labours of M. Pasteur, •
a few remarks supplementary to those of tyL Eadot
may be introduced here. The days when angels
whispered into the hearkening human ear, secrets
which had no root in man's previous knowledge or
experience, are gone for ever. The only revelation—
and surely it deserves the name — now open to the wise
arises from ' intending the mind ' on acquired know-
ledge. When, therefore, M. Eadot, following M. Pas- i/
teur, speaks with such emphasis about ' preconceived
ideas/ he does not mean ideas without antecedents.
Preconceived ideas, if out of deference to M. Pasteur
the term be admitted, are the vintage of garnered
facts. We in England should rather call them induc-
tions, which, as M. Pasteur truly says, inspire the
mind, and shape its course, in the subsequent work
of deduction and verification.

At the time when M. Pasteur undertook his inves-
tigation of the diseases of silkworms, which led to
such admirable results, he had never seen a silkworm ; ^
but, so far from this being considered a disqualification,
M. Dumas regarded his freedom from preconceived
ideas a positive advantage. His first care was to
make himself acquainted with what others had done.
To their observations he added his own, and then,

XIV INTRODUCTION.

surveying all, came to the conclusion that the origin
of the disease was to be sought, not in the worms, not
in the eggs, but in the moths which laid the eggs. I
am not sure that this conclusion is happily described
as ' a preconceived idea.' Every whipster may have
his preconceived ideas ; but the divine power, so
largely shared by M. Pasteur, of distilling from facts
their essences — of extracting from them the principles
from which they flow — is given only to a few.

With regard to the discovery of crystalline facets
in the tartrates, which has been dwelt upon by
M. Eadot, a brief reference to antecedent labours may
be here allowed. It had been discovered by Arago,
in 1811, and by Biot, in 1812 and 1818, that a plate
of rock-crystal, cut perpendicular to the axis of the
prism, possessed the power of rotating the plane of
polarisation through an angle, dependent on the thick-
ness of the plate and the refrangibility of the light.
It had, moreover, been proved by Biot that there existed
two species of rock-crystal, one of which turned the
plane of polarisation to the right, and the other to the
left. They were called, respectively, right-handed and
left-handed crystals. No external difference of crystal-
line form was at first noticed which could furnish a
clue to this difference of action. But closer scrutiny
revealed upon the crystals minute facets, which, in
the one class, were ranged along a right-handed, and,

INTRODUCTION. XV

in the other, along a left-handed spiral. The symmetry
of the hexagonal prism, and of the two terminal
pyramids of the crystal, was disturbed by the intro-
duction of these spirally-arranged facets. They con-
stituted the outward and visible sign of that inward
and invisible molecular structure which produced the
observed action, and difference of action, on polarised
light.

When, therefore, the celebrated Mitscherlich
brought forward his tartrates and paratartrates of
ammonia and soda, and affirmed them to possess the
same atoms the same internal arrangement of atoms,
and the same outward crystalline form, one of them,
nevertheless, causing the plane of polarisation to
rotate, while the other did not, Pasteur, remember-
ing, no doubt, the observations just described, insti-
tuted a search for facets like those discovered in
rock-crystal, and which, without altering chemical
constitution, destroyed crystalline identity. He first
found such facets in the tartrates, while he subse-
quently proved the neutrality of the paratartrate tu
be due to the equal admixture of right-handed and
left-handed crystals, one of which, when the para-
tartrate was dissolved, exactly neutralised the other.

Prior to Pasteur the left-handed tartrate was
unknown. Its discovery, moreover, was supplemented
by a series of beautiful researches on the compounds of
right-handed and left-handed tartaric acid ; he having

a

XVI INTRODUCTION.

previously extracted from the two tartrates, acids which,
in regard to polarised light, behaved like themselves.
Such was the worthy opening of M. Pasteur's scientific-
career, which has been dwelt upon so frequently and
emphatically by M. Eadot. The wonder, however,
is, not that a searcher of such penetration as Pasteur
should have discovered the facets of the tartrates,
but that an investigator so powerful and experienced
as Mitscherlich should have missed them.

The idea of molecular dissymmetry, introduced
by Biot, was forced upon Biot's mind by the discovery
of a number of liquids, and of some vapours, which
possessed the rotatory power. Some, moreover, turned
the plane of polarisation to the right, others to the
left. Crystalline structure being here out of the
question, the notion of dissymmetry, derived from
the crystal, was transferred to the molecule. ' To
produce any such phenomena,' says Sir John Herschel,
' the individual molecule must be conceived as un-
symnietrically constituted.' The illustrations employed
by M. Pasteur to elucidate this subject, though well
calculated to give a general idea of dissymmetry, will,
I fear, render but little aid to the reader in his at-
tempts to realise molecular dissymmetry. Should
-difficulty be encountered here at the threshold of this
work, I would recommend the reader not to be daunted
by it, or prevented by it from going further. He may
comfort himself by the assurance that the conception

INTRODUCTION. xvii

of a dissymmetric molecule is not a very precise one,
even in the mind of M. Pasteur.

One word more with regard to the parentage of
preconceived ideas. M. Kadot informs us that at
Strasburg M. Pasteur invoked the aid of helices and
magnets, with a view to rendering crystals dissym-
metrical at the moment of their formation. There
can, I think, be but little doubt that such experiments
were suggested by the pregnant discovery of Faraday
published in 1845. By both helices and magnets
Faraday caused the plane of polarisation in perfectly
neutral liquids and solids to rotate. If the turning of
the plane of polarisation be a demonstration of mole-
cular dissymmetry, then, in the twinkling of an eye,
Faraday was able to displace symmetry by dissym-
metry, and to confer upon bodies, which in their
ordinary state were inert and dead, this power of
rotation which M. Pasteur considers to be the ex-
clusive attribute of life.

The conclusion of M. Pasteur here referred to,
which M. Kadot justly describes as ' worthy of the
most serious consideration,' is sure to arrest the
attention of a large class of people, who, dreading
' materialism,' are ready to welcome any generalisa-
tion which differentiates the living world from the
dead. M. Pasteur considers that his researches point
to an irrefragable physical barrier between organic
and inorganic nature. Never, he says, have you bean

xvhl INTRODUCTION.

«ible to produce in the laboratory, by the ordinary
processes of chemistry, a dissymmetric molecule — in
other words, a substance which, in a state of solution,
where molecular forces are paramount, has the power
of causing a polarised beam to rotate. This power
belongs exclusively to derivatives from the living world,
~f Dissymmetric/orces, different from those of the labora-
tory, are, in Pasteur's mind, the agents of vitality ; it is
they that build up dissymmetric molecules which baffle
the chemist when he attempts to reproduce them. Such
molecules trace their ancestry to life alone. ' Pour-
rait-on indiquer une separation plus profonde entre les
produits de la nature vivante, et ceux de la nature
miner ale, que cette dissymmetric chez les uns, et son
absence chez les autres ? ' It may be worth calling
to mind that molecular dissymmetry is the idea, or
inference, the observed rotation of the plane of polari-
sation, by masses of sensible magnitude, being the fact
on which the inference is based.

That the molecule, or unit brick, of an organism
should be different from the molecule of a mineral is
only to be expected, for otherwise the profound dis-
tinction between them would disappear. And that
one of the differences between the two classes of
molecules should be the possession, by the one, of
this power of rotation, and its non-possession by the
other, would be a fact, interesting no doubt, but not
surprising. The critical point here has reference to

INTRODUCTION. XIX

the power and range of chemical processes, apart from
the play of vitality. Beginning with the elements
themselves, can they not be so combined as to produce
organic compounds ? Not to speak of the antecedent
labours of Wohler and others in Germany, it is well
known that various French investigators, among whom
are some of M. Pasteur's illustrious colleagues of the
Academy, have succeeded in forming substances which
were once universally regarded as capable of being
elaborated by plants and animals alone. Even with
regard to the rotation of the plane of polarisation, M.
Jungfleisch, an extremely able pupil of the celebrated
Berthelot, affirms, that the barrier erected by M. Pas-
teur has been broken down ; and though M. Pasteur
questions this affirmation, it is at least hazardous,
where so many supposed distinctions between organic
and inorganic have been swept away, to erect a new
one. For my part, I frankly confess my disbelief in
its permanence.

Without waiting for new facts, those already in
our possession tend, I think, to render the association
which 3VL Pasteur seeks to establish between dissym-
metry and life insecure. Quartz, as a crystal, exerts
a very powerful twist on the plane of polarisation.
Quartz dissolved exerts no power at all. The mole-
cules of quartz, then, do not belong to the same category
as the crystal of which they are the constituents ; the
former are symmetrical, the latter is dissymmetrical.

XX INTRODUCTION".

This, in my opinion, is a very significant fact. By the
act of crystallisation, and without the intervention of
life, the forces of molecules, possessing planes of sym-
metry, are so compounded as to build up crystals which
have no planes of symmetry. -Thus, in passing from
the symmetrical to the dissymmetrical, we are not com-
pelled to interpolate new forces ; the forces extant in
mineral nature suffice. The reasoning which applies
to the dissymmetric crystal applies to the dissymmetric
molecule. The dissymmetry of the latter, however
pronounced and complicated, arises from the compo-
sition of atomic forces which, when reduced to their
most elementary action, are exerted along straight
lines. In 1865 I ventured, in reference to this subject,
to define the position which I am still inclined to main-
tain. * It is the compounding, in the organic world
of forces belonging equally to the inorganic that con-
stitutes the mystery and the miracle of vitality.' l

Add to these considerations the discovery of
Faraday already adverted to. An electric current is
not an organism, nor does a magnet possess life ; still,
by their action, Faraday, in his first essay, converted
over one hundred and fifty symmetric and inert
aqueous solutions into dissymmetric and active ones.2

1 Art. ' Vitality,' Fragments of Science, 6th edit., vol. ii. p. 50.

2 In Faraday's induced dissymmetry the ray, having once passed
through the body under magnetic influence, has its rotation doubled,'
instead of neutralised, as in the ease of quartz, on being reflected
back through the body. Marbach has discovered that chlorate of

INTRODUCTION. XXI

Theory, however, may change, and inference may
fade away, but scientific experiment endures for ever.
Such durability belongs, in the domain of molecular
physics, to the experimental researches of M. Pasteur.

The weightiest events of life sometimes turn upon
small hinges ; and we now come to the incident which
caused M. Pasteur to quit a line of research the
abandonment of which he still regrets. A German
manufacturer of chemicals had noticed that the im-
pure commercial tartrate of lime, sullied with organic
matters of various kinds, fermented on being dissolved
in water and exposed to summer heat. Thus prompted,
Pasteur prepared some pure, right-handed tartrate of
ammonia, mixed with it albuminous matter, and found
that the mixture fermented. His solution, limpid at
first, became turbid, and the turbidity he found to be
due to the multiplication of a microscopic organism,
which found in the liquid its proper aliment. Pasteur
recognised in this little organism a living ferment.
This bold conclusion was doubtless strengthened, if
not prompted, by the previous discovery of the yeast-
plant — the alcoholic ferment — by Cagniard-Latour
and Schwann.

Pasteur next permitted his little organism to take

soda produces circular polarisation in all directions through the
rystal, while in quartz it occurs only in the direction of the axis
Marbach also discovered facets upon his crystals, resembling those
of quartz.

XXII INTKODUCTION.

the carbon necessary for its growth from the pure
paratartrate of ammonia. Owing to the opposition
of its two classes of crystals, a solution of this salt,
it will be remembered, does not turn the plane of polar-
ised light either to the right or to the left. Soon
after fermentation had set in, a rotation to the left
was noticed, proving that the equilibrium previously
existing between the twro classes of crystals had ceased.
The rotation reached a maximum, after which it was
found that all the right-handed tartrate had disap-
peared from the liquid. The organism thus proved
itself competent to select its own food. It found, as
it were, one of the tartrates more digestible than the
other, and appropriated it, to the neglect of the other.
No difference of chemical constitution determined its
choice ; for the elements, and the proportions of the
elements, in the two tartrates were identical. But the
peculiarity of structure which enabled the substance to
rotate the plane of polarisation to the right, also ren-
dered it a fit aliment for the organism. This most
remarkable experiment was successfully made with the
seeds of our common mould, Penidllium glaucum.

Here we find Pasteur unexpectedly landed amid
the phenomena of fermentation. With true scientific
instinct he closed with the conception that ferments
are, in all cases, living things, and that the substances
formerly regarded as ferments are, in reality, the
food of the ferments. Touched by this wand, diffi-

INTRODUCTION, XX111

cutties fell rapidly before him. He proved the ferment
of lactic acid to be an organism of a certain kind.
The ferment of butyric acid he proved to be an
organism of a different kind. He was soon led to the
fundamental conclusion that the capacity of an organ-
ism to act as a ferment depended on its power to live
without air. The fermentation of beer was sufficient
to suggest this idea. The yeast-plant, like many others,
can live either with or without free air. It flourishes
best in contact with free air, for it is then spared
the labour of wresting from the malt the oxygen
required for its sustenance. Supplied with free air,
however, it practically ceases to be a ferment ; while
in the brewing vat, where the work of fermentation
is active, the budding tonda is completely cut off by
the sides of the vessel, and by a deep layer of carbonic
acid gas, from all contact with air. The butyric fer-
ment not only lives without air, but Pasteur showed
that air is fatal to it. He finally divided microscopic
organisms into two great classes, which he named
respectively cerobies and ancerobies, the former requir-
ing free oxygen to maintain life, the latter capable of
living without free oxygen, but able to wrest this
element from its combinations with other elements.
This destruction of pre-existing compounds and forma-
tion of new ones, caused by the increase and multipli-
cation of the organism, constitute the process of
fermentation.

XXIV INTRODUCTION.

Under this head are also rightly ranked the phe-
nomena of putrefaction. As M. Eadot well expresses
it, the fermentation of sugar may be described as the
putrefaction of sugar. In this particular field M.
Pasteur, whose contributions to the subject are of the
highest value, was preceded by Schwann, a man of
great merit, of whom the world has heard too little.1
Schwann placed decoctions of meat in flasks, sterilised
the decoctions by boiling, and then supplied them with
calcined air, the power of which to support life he
showed to be unimpaired. Under these circumstances
putrefaction never set in. Hence the conclusion of
Schwann, that putrefaction was not due to the contact
of air, as affirmed by Gay-Lussac, but to something
suspended in the air which heat was able to destroy.
This something consists of living organisms which
nourish themselves at the expense of the organic
substance, and cause its putrefaction.

The grasp of Pasteur on this class of subjects
was embracing. He studied acetic fermentation, and
found it to be the work of a minute fungus, the my-
coderma aeeti, which, requiring free oxygen for its
nutrition, overspreads the surface of the fermenting
liquid. By the alcoholic ferment the sugar of the
grape-juice is transformed into carbonic acid gas and

1 It was late in the day when the Kcyal Society made him a
foreign member.

INTRODUCTION, XXV

alcohol, the former exhaling, the latter remaining in
the wine. By the mycoderma aceti the wine is, in its
turn, converted into vinegar. Of the experiments made
in connection with this subject one deserves especial
mention. It is that in which Pasteur suppressed all
albuminous matters, and carried on the fermentation
with purely crystallisable substances. He studied the
deterioration of vinegar, revealed its cause, and the
means of preventing it. He denned the part played
by the little eel-like organisms which sometimes swarm
in vinegar casks, and ended by introducing important
ameliorations and improvements in the manufacture of
vinegar. The discussion with Liebig and other minor
discussions of a similar nature, which M. Eadot has
somewhat strongly emphasized, I will not here dwell
upon.

It was impossible for an inquirer like Pasteur to
evade the question — Whence come these minute
organisms which are demonstrably capable of pro-
ducing effects on which vast industries are built and
on which whole populations depend for occupation
and sustenance ? He thus found himself face to face
with the question of spontaneous generation, to which
the researches of Pouchet had just given fresh interest.
Trained as Pasteur was in the experimental sciences,
he had an immense advantage over Pouchet, whose
culture was derived from the sciences of observation.

XXVI INTRODUCTION

One by one the statements and experiments of Pouchet
were explained or overthrown, and the doctrine of
spontaneous generation remained discredited until it
was revived with ardour, ability, and, for a time, with
success, by Dr. Bastian.

A remark of M. Eadot's on page 103 needs some
qualification. ' The great interest of Pasteur's method
consists,' he says, ' in its proving unanswerably that
the origin of life in infusions which have been heated
to the boiling point is solely due to the solid particles
suspended in the air.' This means that living germs
cannot exist in the liquid when once raised to a tem-
perature of 212° Fahr. No doubt a great number of
organisms collapse at this temperature ; some indeed,
as M. Pasteur has shown, are destroyed at a tempera-
ture 90° below the boiling point. But this is by no
means universally the case. The spores of the hay-
bacillus, for example, have, in numerous instances, suc-
cessfully resisted the boiling temperature for one, two,
three, four hours ; while in one instance eight hours'
continuous boiling failed to sterilise an infusion of
desiccated hay. The knowledge of this fact caused
me a little anxiety some years ago when a meeting was
projected between M. Pasteur and Dr. Bastian. For
though, in regard to the main question, I knew that
the upholder of spontaneous generation could not win,
on the particular issue touching the death temperature
he might have come off victor.

INTRODUCTION. XXvii

The manufacture and maladies of wine next
occupied Pasteur's attention. He had, in fact, got
the key to this whole series of problems, and he knew
how to use it. Each of the disorders of wine was
traced to its specific organism, which, acting as a
ferment, produced substances the reverse of agreeable
to the palate. By the simplest of devices, Pasteur, at
a stroke, abolished the causes of wine disease. Fortu-
nately the foreign organisms which, if unchecked,
destroy the best red wines are extremely sensitive to
heat. A temperature of 50° Cent. (122° Fahr.) suffices
to kill them. Bottled wines once raised to this tem-
perature, for a single minute, are secured from subse-
quent deterioration. The wines suffer in no degree
from exposure to this temperature. The manner in
which Pasteur proved this, by invoking the judgment
of the wine-tasters of Paris, is as amusing as it is
interesting.

Moved by the entreaty of his master, the illustrious
Dumas, Pasteur took up the investigation of the
diseases of silkworms at a time when the silk-husbandry
of France was in a state of ruin. In doing so he did
not, as might appear, entirely forsake his former line
of research. Previous investigators had got so far as
to discover vibratory corpuscles in the blood of the
diseased worms, and with such corpuscles Pasteur had
already made himself intimately acquainted. He was

XXY111 INTEODUCTION.

therefore to some extent at home in this new investi-
gation. The calamity was appalling, all the efforts
made to stay the plague having proved futile. In
June 1865 Pasteur betook himself to the scene of the
epidemic, and at once commenced his observations.
On the evening of his arrival he had already discovered
the corpuscles, and shown them to others. Acquainted
as he was with the work of living ferments, his mind
was prepared to see in the corpuscles the cause of the
epidemic. He followed them through all the phases
of the insect's life — through the eggs, through the
worm, through the chrysalis, through the moth. He
proved that the germ of the malady might be present
in the eggs and escape detection. In the worm also
it might elude microscopic examination. But in the
moth it reached a development so distinct as to ren-
der its recognition immediate. From healthy moths
healthy eggs were sure to spring ; from healthy eggs
healthy worms ; from healthy worms fine cocoons : so
that the problem of the restoration to France of its
silk-husbandry reduced itself to the separation of the
healthy from the unhealthy moths, the rejection of
the latter, and the exclusive employment of the eggs
of the former. M. Kadot describes how this is now
done on the largest scale, with the most satisfactory
results.

The bearing of this investigation on the parasitic
theory of communicable diseases was thus illustrated :

INTRODUCTION.

Worms were infected by permitting them to feed for
a single meal on leaves over which corpusculous
matter had been spread; they were infected by in-
oculation, and it was shown how they infected each
other by the wounds and scratches of their own claws.
By the association of healthy with diseased worms,
the infection was communicated to the former. In-
fection at a distance was also produced by the wafting
of the corpuscles through the air. The various modes
in which communicable diseases are diffused among
human populations were illustrated by Pasteur's
treatment of the silkworms. ' It was no hypothetical,
infected medium — no problematical pythogenic gas —
that killed the worms. It was a definite organism.' !
The disease thus far described is that called pebrine,
which was the principal scourge at the time. Another
formidable malady was also prevalent, called flacherie,
the cause of which, and the mode of dealing with it,
were also pointed out by Pasteur.

Overstrained by years of labour in this field,
Pasteur was smitten with paralysis in October 1868.
But this calamity did not prevent him from making
a journey to Alais in January 1869, for the express
purpose of combating the criticisms to which his
labours had been subjected. Pasteur is combustible,
and contradiction readily stirs him into flame. No

1 These words were uttered at a time when the pythogenic theory
was more in favour than it is now.

XXX INTRODUCTION.

scientific man now living has fought so many battles
as he. To enable him to render his experiments
decisive, the French Emperor placed a villa at his dis-
posal near Trieste, where silkworm culture had been
carried on for some time at a loss. The success here
is described as marvellous ; the sale of cocoons giving
to the villa a net profit of twenty- six millions of francs.1
From the Imperial villa M. Pasteur addressed to me
a letter, a portion of which I have already published.
It may perhaps prove usefully suggestive to our Indian
or Colonial authorities if I reproduce it here :—

* Permettez-moi de terminer ces quelques lignes que
je dois dieter, vaincu que je suis par la maladie, en
vous faisant observer que vous rendriez service aux
Colonies de la Grande-Bretagne en repandant la con-
naissance de ce livre, et des principes que j'etablis
touchant la maladie des vers a soie. Beaucoup de ces
colonies pourraient cultiver le murier avec succes, et,
en jetant les yeux sur mon ouvrage, vous vous con-
vaincrez aisement qu'il est facile aujourd'hui, non-
seulement d'eloigner la maladie regnante, mais en
outre de donner aux recoltes de la soie une prosperite
qu'elles n'ont jamais eue.'

The studies on wine prepare us for the * Studies
on Beer,' which followed the investigation of silkworm

1 The work on Diseases of Silkworms was dedicated to tho
Empress of the French.

INTRODUCTION. XXXI

diseases. The sourness, putridity, and other maladies
of beer Pasteur traced to special ' ferments of disease,'
of a totally different form, and therefore easily dis-
tinguished from tihe true torula or yeast-plant. Many
mysteries of our breweries were cleared up by this
inquiry. Without knowing the cause, the brewer
not unfrequently incurred heavy losses through the
use of bad yeast. Five minutes' examination with the
microscope would have revealed to him the cause of
the badness, and prevented him from using the yeast.
He would have seen the true torula overpowered by
foreign intruders. The microscope is, I believe, now
everywhere in use. At Burton-on-Trent its aid was
very soon invoked. At the conclusion of his studies
on beer M. Pasteur came to London, where I had the
pleasure of conversing with him. Crippled by paraly-
sis, bowed down by the sufferings of France, and
anxious about his family at a troubled and an un-
certain time, he appeared low in health and depressed
in spirits. His robust appearance when he visited
London, on the occasion of the Edinburgh Anniver-
sary, was in marked and pleasing contrast with my
memory of his aspect at the time to which I have
referred.

While these researches were going on, the Germ
Theory of infectious disease was noised abroad. The
researches of Pasteur were frequently referred to as

b

XXXli INTRODUCTION.

bearing upon the subject, though Pasteur himself
kept clear for a long time of this special field of in-
quiry. He was not a physician, and he did not feel
called upon to trench upon the physician's domain.
And now I would beg of him to correct me if, at this
point of the Introduction, I should be betrayed into
any statement that is not strictly correct.

In 1876 the eminent microscopist, Professor Cohn
of Breslau, was in London, and he then handed me
a number of his ' Beitrage,' containing a memoir
by Dr. Koch on Splenic Fever (Milzbrand, Charbon,
Malignant Pustule), which seemed to me to mark an
epoch in the history of this formidable disease. With
admirable patience, skill, and penetration, Koch fol-
lowed up the life history of bacillus anthracis, the con-
tagium of this fever. At the time here referred to he
was a young physician holding a small appointment
in the neighbourhood of Breslau, and it was easy to
predict, as I predicted at the time, that he would soon
find himself in a higher position. When I next heard
of him he was head of the Imperial Sanitary Institute
of Berlin. Koch's recent history is pretty well known
in England, while his appreciation by the German
Government is shown by the rewards and honours
lately conferred upon him.

Koch was not the discoverer of the parasite of
splenic fever. Davaine and Eayer, in 1850, had ob-
served the little microscopic rods in the blood of

INTRODUCTION. xxxiii

animals which had died of splenic fever. But they
were quite unconscious of the significance of their
observation, and for thirteen years, as M. Eadot informs
us, strangely let the matter drop. In 1863 Davaine's
attention was again directed to the subject by the
researches of Pasteur, and he then pronounced the
parasite to be the cause of the fever. He was opposed
by some of his fellow-countrymen ; long discussions
followed, and a second period of thirteen years, ending
with the publication of Koch's paper, elapsed, before
M. Pasteur took up the question. I always, indeed,
assumed that from the paper of the learned German
came the impulse towards a line of inquiry in which
M. Pasteur has achieved such splendid results. Things
presenting themselves thus to my mind, M. Eadot
will, I trust, forgive me if I say that it was with
very great regret that I perused the disparaging
references to Dr. Koch which occur in the chapter
on splenic fever.

After Koch's investigation, no doubt could be en-
tertained of the parasitic origin of this disease. It
completely cleared up the perplexity previously existing
as to the two forms — the one fugitive, the other per-
manent— in which the contagium presented itself. I
may say that it was on the conversion of the per-
manent hardy form into the fugitive and sensitive one,
in the case of bacillus subtilis and other organisms, that
the method of sterilising by ' discontinuous heating '

b2

XXXIV INTRODUCTION.

introduced by me in February 1877 was founded. The
difference between an organism and its spores, in point
of durability, had not escaped the penetration of
Pasteur. This difference Koch showed to be of para-
mount importance in splenic fever. He, moreover,
proved that while mice and guinea-pigs were infallibly
killed by the parasite, birds were able to defy it.

And here we come upon what may be called a hand-
specimen of the genius of Pasteur, which strikingly
illustrates its quality. Why should birds enjoy the
immunity established by the experiments of Koch ?
Here is the answer. The temperature which prohibits
the multiplication of bacillus anthracis in infusions is
44° Cent. (111° Fahr.). The temperature of the blood
of birds is from 41° to 42°. It is therefore close to
the prohibitory temperature. But then the blood
globules of a living fowl are sure to offer a certain
resistance to any attempt to deprive them of their
oxygen — a resistance not experienced in an infusion.
May not this resistance, added to the high tempera-
ture of the fowl, suffice to place it beyond the power
of the parasite? Experiment alone could answer
this question, and Pasteur made the experiment.
By placing its feet in cold water he lowered the tem-
perature of a fowl to 87° or 38°. He inoculated
the fowl, thus chilled, with the splenic fever parasite,
and in twenty- four hours it was dead. The argu-
ment was clinched by inoculating a chilled fowl, per-

INTRODUCTION. XXXV

mitting the fever to come to a head, and then remov-
ing the fowl, wrapped in cotton-wool, to a chamber
with a temperature of 35°. The strength of the
patient returned as the career of the parasite was
brought to an end, and in a few hours health was
restored. The sharpness of the reasoning here is
only equalled by the conclusiveness of the experiment,
which is full of suggestiveness as regards the treat-
ment of fevers in man.

Pasteur had little difficulty in establishing the
parasitic origin of fowl cholera ; indeed, the parasite
had been observed by others before him. But by his
successive cultivations, he rendered the solution sure,
His next step will remain for ever memorable in the
history of medicine. I allude to what he calls * virus
attenuation.' And here it may be well to throw out
a few remarks in advance. When a tree, or a bundle
of wheat or barley straw, is burnt, a certain amount of
mineral matter remains in the ashes — extremely small
in comparison with the bulk of the tree or of the straw,
but absolutely essential to its growth. In a soil lacking,
or exhausted of, the necessary mineral constituents, the
tree cannot live, the crop cannot grow. Now contagia
are living things, which denmnd certain elements of life
just as inexorably as trees, or wheat, or barley ; and it
is not difficult to see that a crop of a given parasite may
so far use up a constituent existing in small quantities

XXXvi INTRODUCTION.

in the body, but essential to the growth of the parasite,
as to render the body unfit for the production of a
second crop. The soil is exhausted, and, until the
lost constituent is restored, the body is protected
from any further attack of the same disorder. Such
an explanation of non-recurrent diseases naturally
presents itself to a thorough believer in the germ
theory, and such was the solution which, in reply to
a question, I ventured to offer nearly fifteen years
ago to an eminent London physician. To exhaust a
soil, however, a parasite less vigorous and destructive
than the really virulent one may suffice ; and if, after
having by means of a feebler organism exhausted the
soil, without fatal result, the most highly virulent
parasite be introduced into the system, it will prove
powerless. This, in the language of the germ theory,
is the whole secret of vaccination.

The general problem, of which Jenner's discovery
was a particular case, has been grasped by Pasteur, in
a manner, and with results, which five short years ago
were simply unimaginable. How much ' accident '
had to do with shaping the course of his enquiries
I know not. A mind like his resembles a photo-
graphic plate, which is ready to accept and develop
luminous impressions, sought and unsought. In the
chapter on fowl cholera is described how Pasteur first
obtained his attenuated virus. By successive cultiva-
tions of the parasite he showed, that after it had been

INTRODUCTION. XXXVii

a hundred times reproduced, it continued to be as
virulent as at first. One necessary condition was,
however, to be observed. It was essential that the
cultures should rapidly succeed each other — that the
organism, before its transference to a fresh cultivating
liquid, should not be left long in contact with air.
When exposed to air for a considerable time the virus
becomes so enfeebled that when fowls are inoculated
with it, though they sicken for a time, they do not
die. But this ' attenuated ' virus, which M. Kadot
justly calls 'benign,' constitutes a sure protection
against the virulent virus. It so exhausts the soil
that the really fatal contagium fails to find there the
elements necessary to its reproduction and multipli-
cation.

Pasteur affirms that it is the oxygen of the air
which, by lengthened contact, weakens the virus and
converts it into a true vaccine. He has also weakened
it by transmission through various animals. It was
this form of attenuation that was brought into play
in the case of Jenner.

The secret of attenuation had thus become an open
one to Pasteur. He laid hold of the murderous virus
of splenic fever, and succeeded in rendering it, not
only harmless to life, but a sure protection against the
virus in its most concentrated form. No man, in my
opinion, can work at these subjects so rapidly as
Pasteur without falling into errors of detail. But this

XXXVlll INTRODUCTION.

may occur while his main position remains impreg-
nable. Such a result, for example, as that obtained
in presence of so many witnesses at Melun must
surely remain an ever-memorable conquest of science.
Having prepared his attenuated virus, and proved, by
laboratory experiments, its efficacy as a protective
vaccine, Pasteur accepted an invitation from the
President of the Society of Agriculture at Melun, to
make a public experiment on what might be called an
agricultural scale. This act of Pasteur's is, perhaps,
the boldest thing recorded in this book. It naturally
caused anxiety among his colleagues of the Academy,
who feared that he had been rash in closing with the
proposal of the President.

But the experiment was made. A flock of sheep
was divided into two groups, the members of one group
being all vaccinated with the attenuated virus, while
those of the other group were left unvaccinated A
number of cows were also subjected to a precisely
similar treatment. Fourteen days afterwards, all the
sheep and all the cows, vaccinated and unvaccinated,
were inoculated with a very virulent virus ; and three
days subsequently more than two hundred persons
assembled to witness the result. The ' shout of
admiration,' mentioned by M. Eadot, was a natural
outburst under the circumstances. Of twenty-five
sheep which had not been protected by vaccination,
twenty-one were already dead, and the remaining ones

INTKODUCTION. XXxix

were dying. The twenty-five vaccinated sheep, on
the contrary, were ' in full health and gaiety.' In the
unvaccinated cows intense fever was produced, while
the prostration was so great that they were unable
to eat. Tumours were also formed at the points of
inoculation. In the vaccinated cows no tumours were
formed ; they exhibited no fever, nor even an elevation
of temperature, while their power of feeding was
unimpaired. No wonder that ' breeders of cattle over-
whelmed Pasteur with applications for vaccine.' At
the end of 1881 close upon 34,000 animals had been
vaccinated, while the number rose in 1883 to nearly
500,000.

M. Pasteur is now exactly sixty-two years of
age ; but his energy is unabated. At the end of
this volume we are informed that he has already
taken up and examined with success, as far as his
experiments have reached, the terrible and mysterious
disease of rabies or hydrophobia. Those who hold all
communicable diseases to be of parasitic origin, in-
clude, of course, rabies among the number of those
produced and propagated by a living contagium. From
his first contact with the disease Pasteur showed his
accustomed penetration. If we see a man mad, we at
once refer his madness to the state of his brain. It is
somewhat singular that in the face of this fact the
virus of a mad dog should be referred to the animal's

xl INTRODUCTION.

saliva. The saliva is, no doubt, infected, but Pasteur
soon proved the real seat and empire of the disorder
to be the nervous system.

The parasite of rabies had not been securely
isolated when M. Eadot finished his task. But last
May, at the instance of M. Pasteur, a commission
was appointed by the Minister of Public Instruction
in France, to examine and report upon the results
which he had up to that time obtained. A preliminary
report, issued to appease public impatience, reached
me before I quitted Switzerland this year. It inspires
the sure and certain hope that, as regards the attenu-
ation of the rabic virus, and the rendering of an
animal, by inoculation, proof against attack, the
success of M. Pasteur is assured. The commission,
though hitherto extremely active, is far from the end
of its labours ; but the results obtained so far may
be thus summed up :—

Of six dogs unprotected by vaccination, three
succumbed to the bites of a dog in a furious state of
madness.

Of eight unvaccinated dogs, six succumbed to the
intravenous inoculation of rabic matter.

Of five unvaccinated dogs, all succumbed to inocu-
lation, by trepanning, of the brain.

Finally, of three-and-twenty vaccinated dogs, not
one was attacked with the disease subsequent to
inoculation with the most potent virus.

INTRODUCTION. xli

Surely results such as those recorded in this
book are calculated, not only to arouse public
interest, but public hope and wonder. Never before,
during the long period of its history, did a day like
the present dawn upon the science and art of medi-
cine. Indeed, previous to the discoveries of recent
times, medicine was not a science, but a collection of
empirical rules dependent for their interpretation and
application upon the sagacity of the physician. How
does England stand in relation to the great work now
going on around her ? She is, and must be, behind-
hand. Scientific chauvinism is not beautiful in
my eyes. Still one can hardly see, without depreca-
tion and protest, the English investigator handicapped
in so great a race by short-sighted and mischievous
legislation.

A great scientific theory has never been accepted
without opposition. The theory of gravitation, the
theory of undulation, the theory of evolution, the
dynamical theory of heat— all had to push their way
through conflict to victory. And so it has been with
the Germ Theory of communicable diseases. Some
outlying members of the medical profession dispute
it still. I am told they even dispute the communica-
bility of cholera. Such must always be the course of
things, as long as men are endowed with different
degrees of insight. Where the mind of genius dis-
cerns the distant truth, which it pursues, the mind

xlii INTRODUCTION.

not so gifted often discerns nothing but the extra-
vagance, which it avoids. Names, not yet forgotten,
could be given to illustrate these two classes of minds.
As representative of the first class, I would name a
man whom I have often named before, who, basing
himself in great part on the researches of Pasteur,
fought, in England, the battle of the germ theory with
persistent valour, but whose labours broke him down
before he saw the triumph which he/oresaw completed.
Many of my medical friends will understand that I
allude here to the late Dr. William Budd, of Bristol.

The task expected of me is now accomplished, and
the reader is here presented with a record, in which
the verities of science are endowed with the interest
of romance.

JOHN TYNDALL.

ROYAL INSTITUTION : December 1884.

RECOLLECTIONS OF CHILDHOOD AND
YOUTH.

FIRST DISCOVERIES.

' COME, M. Pasteur ! you must shake off the demon
of idleness ! ' It was the night watcher of the College
of Besan9on, who invariably at four o'clock in the
morning entered Pasteur's room and roused him with
this vigorous salute, which was accompanied, when
necessary, by a sound shaking. Pasteur was then
eighteen years of age. In addition to his food and
lodging, the royal college paid him twenty-four francs
a month. But if his place was a modest one, it suf-
ficed at the time for his ambition : it was the first tie
which bound him to the University.

' Ah,' said his father to him frequently, ' if only
you could become some day professor in the College
of Arbois I should be the happiest man on earth.'

Already, when he resided at Dole, and when his
son was not yet two years old, this father permitted
himself to dream thus of the future. What would he

c c c c | *-. * « LOUIS PASTEUK.

have said had it been announced to him that fifty-
eight years later, on the fa9ade of the little house in
the Eue des Tanneurs, would be placed, in the pre-
sence of his living son — laden with honours, laden with
glory, passing in the midst of a triumphal procession
along the paved town — a plate bearing these words in
letters of gold :

HERE WAS BORN Louis PASTEUR,
December 27, 1822.

Pausing before this house, Pasteur recalled the
image of his father and mother — of those whom he
called his dear departed ones — and from the far-off
depths of his childhood came so many memories of
affection, devotion, and paternal sacrifices that he
burst into tears.

The life of his father had been a rough one. An
old soldier, decorated on the field of battle, on return-
ing to France, where he had no longer a home, he
was obliged to work hard to earn his bread. He took
up the trade of a tanner. Soon afterwards, having
made the acquaintance of a worthy young girl, he
joined his lot with hers, and together they entered
courageously on the labours of their married life —
he calm, reflective, and more eager, whenever he had
a moment of repose, for the society of books than for
the society of his neighbours ; she full of enthusiasm,
her heart and spirit agitated by .thoughts above the

EECOLLECTIONS OF CHILDHOOD 'A^D '-YOUTH.'. . / : 3*.

level of her modest life. Both of them watched with
ceaseless solitude over their little Louis, of whom,
with mingled pride and tenderness, they used to say,
* We will make of him an educated man.'

In 1825 the Pasteur family quitted Dole and esta-
blished themselves at Arbois, where, on the borders
of the Cuisance, the father of our hero had bought a
small tanyard. At this town, and in this yard, Louis
Pasteur spent his childhood. As soon as he was old
enough to be received as a half-pay scholar he was
sent to the communal college. He, the smallest of
all the pupils, was so proud of passing under the great
arched doorway of this ancient establishment, that
he arrived laden with enormous dictionaries, of which
there was no need.

In the midst of his laborious occupations the
father of Pasteur took upon himself the task of super-
intending his son's lessons every evening. This was
at first no sinecure. Louis Pasteur did not always
take the shortest road either to reach his class or to
return to his work at home. Some old friends still
living remember having made with the little Pasteur
fishing parties, which proved so pleasant that they
have been continued to the present day. The boy,
moreover, instead of applying himself to his lessons,
often escaped and amused himself by making large
portraits of his neighbours, male and female. A
dozen of these portraits are still to be seen in the

B 2

4 LOUIS PASTEUK.

houses of Arbois, all bearing his signature. Consider-
ing that his age at the time was only thirteen, the-
accuracy of the drawing is astonishing.

' What a pity,' said an old lady of Arbois a short
time since, * that he should have buried himself in
chemistry ! He has missed his vocation, for he might
by this time have made his reputation as a painter.'

It was not until he reached the third class that
Louis Pasteur, beginning to realise the sacrifices
which his father imposed upon himself, determined to
abandon his fishing implements and his crayons, feel-
ing aroused within him that passion for work which
was to form the foundation of his life. The Principal
of the college, who followed with watchful interest the
progress of a pupil who, in his first effort, had out-
stripped all his comrades, used to say, 'He will go
far. It is not for the chair of a small college like ours
that we must prepare him ; he must become pro-
fessor in a royal college. My little friend,' he would
add, ' think of the great Ecole Norrnale.'

The College of Arbois having no professor of philo-
sophy, Pasteur quitted it for Besan9on. There he
remained for the scholars' year, received the degree of
bachelier es lettres, and was immediately appointed
tutor in the same college. In the intervals of his
duties he followed the course of mathematics neces-
sary to prepare him for the scientific examinations of
the Ecole Norrnale. He must have been already

KECOLLECTIONS OF CHILDHOOD AND YOUTH. 5

endowed with a singular maturity of character, for
the director confided to him the superintendence of
the quarters of the older pupils, who during class time
were his comrades. In the class room his table was
.in the midst of them; and never had so young a
master so much authority, and at the same time so
little need for its exercise.

His first taste for chemistry manifested itself by
frequent questions addressed during class time to an
old professor named Darlay. This questioning was
so often repeated that the good man, quite bewildered,
ended by declaring that it was for him to interrogate
Pasteur and not for Pasteur to interrogate him. His
pupil pressed him no further, but having heard that at
Besan9on there lived an apothecary who had once dis-
tinguished himself by a paper inserted in the ' Annales
de Chimie et de Physique,' he sought this man, with a
view of ascertaining whether, on holidays, he would
consent to give him lessons secretly.

At the examination for the Ecole Normale, Pasteur
passed as fourteenth in the list. This rank, however,
did not satisfy him. Notwithstanding the censure of
his fellow candidates he declared that he would begin a
new year of preparation. It was in Paris itself that he
chose to work — in one of the silent corners of the city,
amid the seclusion of preparatory schools and convents.

In the Impasse des Feuillantines, there lived a
schoolmaster, M. Barbet by name, or rather le pere

6 LOUIS PASTEUR.

Barlet, as the Franc-Conitois, with provincial fami-
liarity, used to call hirn. Pasteur begged to be allowed
to enter his institution, not as an assistant, but as
a simple pupil. Knowing how slender were the means
of his young compatriot, M. Barbet reduced the fees
of his pupil by one-third. Such kindness was cus-
tomary with the pere Barlct, who did not like to be
reminded of his generosity. This, however, gives
double pleasure to him who records it.

The year passes, the time of the examination
arrives, and Pasteur is received as fourth on the list.
Thus at last, in the month of October 1843, he finds
himself in that Ecole Norniale in which he was
destined to take so great a place. Pasteur's taste for
chemistry had become a passion which he could now
satisfy to his heart's content. Chemistry was at this
time taught at the Sorbonne by M. Dumas and at the
Ecole Norniale by M. Balard. The pupils of the Ecole
attended both courses of lectures. Different as were
the two professors, both of them exercised great influ-
ence on their pupils. M. Dumas, with his serene
gravity and his profound respect for his auditory,
never allowed the smallest incorrectness to slip into
his exposition. M. Balard, with a vivacity quite
juvenile, with the excitement of a southerner in the
tribune, did not always give his words time to follow
his thoughts. It was he who once, showing a little
potash to his audience, exclaimed with a fervour which

EECOLLECTIO.NS OF CHILDHOOD AND YOUTH. 7

has become celebrated, 'Potash, which — potash, then
—potash, in short, which I now present to you.'

The general principles which M. Dumas in his
teaching delighted to develop, the multitude of facts
which M. Balard unfolded to his pupils, all answered
to the needs of Pasteur's mind. If he loved the vaster
horizons of science, he was also possessed by the
anxious desire for exactitude, and for the perpetual
control of experiment. Each of the lectures of the
Ecole Normale and of the Sorbonne excited in him
a profound enthusiasm. One day M. Dumas, while
illustrating the solidification of carbonic acid, begged
for the loan of a handkerchief to receive the carbonic
acid snow. Pasteur rushed forward, and, presenting
his handkerchief, received the snow. He returned
triumphant, and running forthwith to the Ecole Nor-
male, repeated the principal experiments which the
illustrious chemist had just exhibited to his audience.
He preserved religiously the handkerchief which had
been touched by M. Dumas.

Pasteur usually spent his Sundays with M. Bar-
ruel, the assistant of M. Dumas. He thought of
nothing but experiments. For a long time in one
of the laboratories of the Ecole Normale was exhibited
a basin — perhaps it is still shown — containing sixty
grammes of phosphorus obtained from bones bought
at the butcher's by Pasteur. These he had calcined,
submitted to the processes known to chemists, and

LOUIS PASTEUR.

finally reduced, after a whole day's heating, from four
in the morning to nine in the evening, to the said
sixty grammes. It was the first time that the long
manipulations required in the preparation of this
simple substance were attempted at the Ecole Nor-
male.

Isolated in laboratory or library, Pasteur's only
thought was to search, to learn, to question, and to
verify. As the rule of the school leaves much to
individual initiative, he devoted himself to his work
with a joyful heart. This daily liberty constitutes
the charm and the honour of the Ecole Normale. Not
only does it permit but it encourages individual effort;
it allows the student to visit at his will the library,
and to consult there the scientific journals and reviews.
This free system of education develops singularly the
spirit of research. There is in it an element of
superiority over the Ecole Poly technique. Influenced
by its military origin, constrained, moreover, by the
number of its pupils to impose on all an exact disci-
pline, and to introduce into their exercises a strict
regularity, the Ecole Polytechnique is, perhaps, less
calculated than the Ecole Normale to awaken in the
minds of its pupils a taste for speculative science.
It is certain that Pasteur owed to the freedom of work,
and to the facilities for solitary reading which he there
enjoyed, the first occasion for an investigation which
was the starting-point to a veritable discovery.

FIRST DISCOVERIES.

L

Unlike the old professor of physics and chemistry
at Besan9on, one of the lecturers in the Ecole Normale
often took pleasure, not only in answering Pasteur's
questions, but in leading him on to talk over scientific
subjects. M. Delafosse, whose memory remains dear
to all his pupils, was one of those men who fail to do
themselves justice, or who, according to the expression
of Cardinal de Ketz, do not fulfil all their merit. Not
that circumstances have been unfavourable to them,
but that an invincible modesty, and a natural non-
chalance which finds in that modesty a shield against
latent self-reproach, leave them in a sort of twilight
in which they are content to dwell. Pupil, and after-
wards fellow worker, of the celebrated crystallographer
Haiiy, M. Delafosse had devoted himself to questions
of molecular physics. Pasteur, who had read with
enthusiasm the works of Haiiy, conversed incessantly
with Delafosse about the arrangements of molecules,
when an unexpected note from the German chemist
Mitscherlich, communicated to the Academy of
Sciences, came to trouble all. his scientific beliefs.
Here is the note : — '

' The paratartrate and the tartrate of soda and
ammonia have the same chemical composition, the
same crystalline form, the same angles, the same

10 LOUIS PASTEUK.

specific weight, the same double refraction, and con-
sequently the same inclination of the optic axes.
Dissolved in water, their refraction is the same. But
while the dissolved tartrate causes the plane of polar-
ised light to rotate, the paratartrate exerts no such
action. M. Biot has found this to be the case with the
whole series of these two kinds of salts. Here (adds
Mitscherlich) the nature and the number of the
atoms, their arrangement, and their distances apart
are the same in the two bodies.'

Imbued as he was with the teachings of Haiiy and
Delafosse, and full of the ideas of M. Dumas in mole-
cular chemistry, Pasteur asked himself this question :
* How can it be admitted that the nature and number
of the atoms, their arrangement and distances apart,
in two chemical substances are the same ; that the
crystalline forms are equally the same, without con-
cluding that the two substances are absolutely iden-
tical ? Is there not a profound incompatibility between
the identity affirmed by Mitscherlich and the dis-
crepancy of optic character manifested by the two
compounds, tartaric and paratartaric, which form the
subject of his note ? '

This difficulty rested in Pasteur's mind with the
tenacity of a fixed idea. Eeceived as agrege of physical
science at the end of his third year at the Ecole, and
then keeping near his master, M. Balard, he had
begun the study of crystals and the determination of

FIRST DISCOVERIES. 11

their angles and forms, when his nomination to the
professorship of physics in the Lycee of Tournon
surprised and distressed him. M. Balard repaired
immediately to the bureau of the Minister of Educa-
tion, and spoke of his assistant in terms which caused
the nomination to be cancelled. Pasteur remained in
the laboratory of the Ecole Normale.

With a view to mastering the science of crystal-
lography, he took for his guide the extensive work
of M. de la Provostaye, resolving to repeat all the
measurements of angles and all the other determina-
tions of this author with a view to a comparison of
their respective results. The work of M. de la Pro-
vostaye, who was distinguished by the exactitude of
his researches, had for its subject the tartaric and
paratartaric acids and their saline compounds.

Two or three years ago, while we were walking to-
gether along a road in the Jura, M. Pasteur, after
quoting textually the note of Mitscherlich, described
to me with enthusiasm the pleasure he had experienced
in crystallising tartaric acid and its salts, the crystals
of which, he said, rivalled in size and beauty the most
exquisite of crystalline forms.

' I should have great difficulty,' I remarked, ' in
following you through the labyrinth of tartaric acid,
tartrates, and paratartrates. However much your
other studies have attracted me, those which had for

12 LOUIS PASTEUE.

their starting-point the note of Mitscherlich and the
memoir of M. de la Provostaye have appeared to me,
whenever I tried to master them, difficult of access.
Ah,' I added, ' you would have done well, out of con-
sideration for those who love to speak of your labours,
had you made no discoveries in this field.'

Pasteur, with a mixture of indignation and indul-
gence, replied : — ' Is it possible that you have not
discerned the grand horizons that lie behind these
researches in physics and molecular optics ? If I
have a regret, it is that I did not follow out this path.
Less rough than it at first sight appears, it would, I
am convinced, have led to the most important dis-
coveries. By a sudden turn it threw me unexpectedly
upon the subject of fermentation, and fermentation
led me to the study of diseases ; but I still continue
to lament that I have never had time to retrace my
steps.'

Then, with a simplicity of exposition in which one
recognised the teacher who had always endeavoured
to place his ideas within the range of his hearers, he
said —

' If you picture to yourself all the bodies in nature
— mineral, animal, or vegetable, and consider even
the objects formed by the hands of man, you will see
that they divide themselves into two great categories.
The one has a plane of symmetry and the other has
not. Take, for instance, a table, a chair, a playing

FIRST DISCOVERIES. 13

die, or the human body; we can imagine a plane
passing through these objects which divides each of
them into two absolutely similar halves. Thus, a
plane passing through the middle of the seat and of
the back of an arm-chair would have, on its right
and left, identical parts ; in like manner a vertical
plane passing through the middle of the forehead,
nose, mouth, and chin of an individual, would have
similar parts to the right and to the left. All these
objects, and a multitude of similar ones, constitute
our first category. They have, as mathematicians
express it, one or several planes of symmetry.

' But, as regards the repetition of similar parts, it
is far from being the case that all bodies are constituted
in the manner here described. Consider, for example,
your right hand : it is impossible to find for it a plane
of symmetry. Whatever be the position of a plane
which you imagine cutting the hand, you will never
find on the right of this plane exactly the same as
you find on its left. The same remark applies to
your left hand, to your right ear and to your left ear,
to your right eye and to your left eye ; to your two
arms, your two legs, and your two feet. The human
body, taken as a whole, has a plane of symmetry,
but none of the parts composing one or the other of
its halves has such a plane. The stalk of a plant
whose leaves are distributed spirally round its stem
has not a plane of symmetry, nor has a spiral stair-

14 LOUIS PASTEUK.

case such a plane ; but a straight one has. You see
this?

' It would have been truly extraordinary, would it
not, if the various kinds of minerals, such as sea salt,
alum, the diamond, rock crystal, and so many others
which illustrate the great law of crystallisation, and
which clothe themselves in geometric forms, should
not present to us examples of the two categories of
which we have just been speaking ? They do so in
fact. Thus a cube, which has the form of a player's
die, has a plane of symmetry ; it has indeed several
planes. The form of the diamond, which is a regular
octahedron, has also several planes of symmetry. It
is thus also with the great majority of the mineral
forms met with in nature or in the laboratory. They
have generally one or several planes of symmetry.
There are, however, exceptions. Kock crystal, which
is found in prisms, often of large volume, in the
fissures of certain primitive rocks, has no plane of
symmetry. This crystal exhibits certain small facets,
distributed in such a manner that in their totality
they might be compared to a helix, or spiral, or
screw, which are all objects not possessing a plane of
symmetry.

* Every object which has a plane of symmetry, when
placed before a looking-glass, has an image which is
rigorously identical with the object itself. The image
can be superposed upon the reality. Place a chair

FIRST DISCOVERIES. 15

before a mirror ; the image faithfully reproduces the
chair. The mirror also reproduces the human body
considered as a whole. But place before the mirror
your right hand and you will see a left hand. The
right hand is not superposable on the left, just as
the glove of your right hand cannot be fitted to your
left, and inversely.'

Then reverting to the beginnings of his studies in
crystallography, Pasteur recounted to me briefly that,
after having gone through the work of M. de la Pro-
vostaye, he perceived that a very interesting fact had
escaped the notice of this skilful physicist. M. de la
Provostaye had failed to observe that the crystalline
forms of tartaric acid and of its compounds all belong
to the group of objects which have not a plane of
symmetry. Certain minute facets had escaped him.
In other words, Pasteur discerned that the crystal-
line form of tartaric acid, placed before a mirror, pro-
duced an image which was not superposable upon the
crystal itself. The same was found to be true of
the forms of all the chemical compounds of this acid.
On the other hand, he imagined that the crystal-
line form of paratartaric acid, and of all the com-
pounds of this acid, would be found to form part
of the group of natural objects which have a plane of
symmetry.

Pasteur was transported with joy by this double
result. He saw in it the possibility of reaching by

16 LOUIS PASTEUE.

experiment the explanation of the difficulty which
the note of Mitscherlich had thrown down as a kind
of challenge to science, when it signalised an optical
difference between two chemical compounds affirmed
to be otherwise rigorously identical. Pasteur reasoned
thus : — Since I find tartaric acid and all its tartrates
without a plane of symmetry, while its isomer, para-
tartaric acid, and its compounds have such a plane, I
will hasten to prepare the tartrate and the paratartrate
of the note of Mitscherlich. I will compare their
forms, and in all probability the tartrate will be found
dissymmetrical — that is to say, without a plane of
symmetry — while the paratartrate will continue to
have such a plane. Henceforward the absolute iden-
tity stated by Mitscherlich to exist between the forms
of these two compounds will have no existence. It
will be proved that he has erred, and his note will no
longer have in it anything mysterious. As the optic
action proper to the tartrates spoken of in his note
manifests itself by a deviation of the plane of polarisa-
tion to the right, we have here a kind of dissymmetry
which has nothing incompatible with the dissymmetry
of form. On the contrary, these two dissymmetries
can be referred to one and the same cause. In like
manner, the absence of dissymmetry in the form of
the paratartrate will be connected with the optical
neutrality of that compound.

The fulfilment of Pasteur's hopes was only partial.

FIRST DISCOVERIES. 17

The tartrates of soda and ammonia presented, as did
all the other tartrates, the dissymmetry manifested by
the absence of any plane of symmetry ; that is to say,
the crystals of this salt placed before a mirror pro-
duced an image which was not superposable upon the
crystal. It was like a right hand having its left for
an image. With regard to the paratartrates of soda
and ammonia, one circumstance struck Pasteur in a
quite unexpected manner. Far from establishing in
the crystals of this salt the absence of all dissymmetry,
he found that they all manifestly possessed it. But,
strange to say, certain crystals possessed it in one
sense and other crystals in a sense opposite. Some
of these crystals, when placed before a mirror, produced
the image of the others, and one of the two kinds of
crystals corresponded rigorously in form with the tar-
trate prepared by means of the tartaric acid of the
grape. Pasteur continued his reasoning thus : — Since
there is no difference between the form of the tartrate
derived from the tartaric acid of the grape and one of
the two kinds of crystals deposited at the moment of
crystallisation of the paratartrate, the simple observa-
tion of the dissymmetry proper to each will enable me
to separate, by hand, all the crystals of the paratartrate
which are identical with those of the tartrate. By
ordinary chemical processes I ought to be able to ex-
tract a tartaric acid identical with that of the grape,
possessing all its physical, mineralogical, and chemical

c

18 LOUIS PASTEUK.

properties — that is to say, a tartaric acid possessing,
like the natural tartaric acid of the grape, dissymmetry
of form, and exerting an action on polarised light.
Per contra, I ought to be able to extract from the
second sort of crystals, associated with the former in
the paratartaric group, an acid which will reproduce
ordinary tartaric acid, but possessing a dissymmetry
of an inverse kind and exerting an action equally in-
verse on polarised light.

With a feverish ardour Pasteur hastened to make
this double experiment. Imagine his joy when he
saw his anticipations not only realised but realised
with an exactitude truly mathematical. His delight
was so great that he quitted the laboratory abruptly.
Hardly had he gone out when he met the assistant of
the physical professor. He embraced him, exclaim-
ing, ' My dear Monsieur Bertrand, I have just made a
great discovery ! I have separated the double para-
tartrate of soda and ammonia into two salts of inverse
dissymmetry, and exerting an inverse action on the
plane of polarisation of light. I am so happy that a
nervous tremulousness has taken possession of me,
which prevents me from looking again through the
polariscope. Let us go to the Luxembourg, and I will
explain it all to you.'

These results excited in a high degree the attention
of the Academy of Sciences, where sat, at the time now
referred to, Arago, Biot, Dumas, De Senarmont, and

FIEST DISCOVERIES, 19

Balarcl. It might be said without exaggeration
that the Academy was astounded. At the same
time there were many members who were slow to be-
lieve in this discovery. Charged with drawing up the
report, M. Biot began by requiring from Pasteur the
verification of each point which he had announced.
To this verification M. Biot brought his habitual pre-
cision, which was associated with a kind of suspicious
scepticism.

In one of his lectures Pasteur thus described his
interview with M. Biot : — ' He made me come to his
house, where he put into my handssome paratartaric
acid which he had carefully studied himself, and found
perfectly neutral as regards polarised light. It was
not in the laboratory of the Ecole Normale, it was in
his own kitchen, and in his presence, that I was to pre-
pare this double salt with soda and ammonia procured
by himself. The liquor was left slowly to evaporate,
and at the end of ten days, when it had deposited
thirty or forty grammes of crystals, he begged me to
go over to the College de France to collect the crystals
and to extract from them specimens of the two kinds,
which he proposed to have placed, the one on his right
hand, the other on his left, desiring me to declare if I
was ready to re-affirm, that the crystals to the right
would turn the plane of polarisation to the right and
the others to the left. This declaration made, he
said that he would charge himself with the rest of

c 2

20 LOUIS PASTEUR.

the inquiry. M. Biot then prepared the solutions in
well-measured proportions, and at the moment of
observing them in the polarising apparatus he invited
.me again to come into his study. He placed first in
the apparatus the most interesting solution, that which
ought to deviate to the left. Without even making any
measurements, he saw, by the mere inspection of the
colours of the ordinary and extraordinary images of the
analyser, that there was a strong deviation to the left.
Visibly moved, the illustrious old man took my arm
and said, "My dear child, I have loved science so well
throughout my life that this makes my heart beat." '

The emotion of M. Biot was all the more profound
because he had been himself the first to discover the
rotation of the plane of polarisation by chemical sub-
stances, and had, for more than thirty years, affirmed
that the study of these substances and of their action
in regard to rotatory polarisation was, perhaps, the
surest means of penetrating into the intimate consti-
tution of bodies. His counsels were received with,
deference, but they had never been followed out. And
now there appeared before the old man, already some-,
what discouraged, a youth of twenty-five, who from his
first investigation had proved himself a master, who
had dissipated the obscurities of the famous German
note, and created a new chapter in crystallographic
chemistry. The composition and nature of paratartaric
acid had been explained, and a new substance, the

FIRST DISCOVERIES. 21

left-handed tartaric acid, with its truly surprising
properties, had been discovered; molecular physics
and chemistry had been enriched with new facts and
theories of great value.

The first care of Pasteur, after having discovered
the. left-handed tartaric acid and the constitution of
paratartaric acid, was to compare very carefully the
properties of the new left-handed acid with those of the
right, endeavouring to determine by strict experiment
the influence on these properties of the internal
atomic arrangements of the two acids. Although we
are unable to picture the exact figure of these atomic
groupings, there can be no doubt that they are formed
of the same elementary particles, that they are, more-
over, dissymmetrical, and that, in short, the dissymme-
try of the one group is the same as that of the other,
but in an inverse sense. If, for example, the arrange-
ment of the atoms of the right-handed tartaric acid
present the exterior appearance of an irregular pyra-
mid, the arrangement of the atoms of the left-handed
tartaric acid ought, of necessity, to present the form
of a pyramid irregular in the inverse sense.

II.

Nominated assistant professor of chemistry at
Strasburg, Pasteur followed up with enthusiasm these
curious studies. To interrupt them for an instant it

22 LOUIS PASTEUK.

required nothing less than his engagement with
Mademoiselle Marie Laurent, daughter of the Eector
of the Academy. It is even asserted that on the very
morning of his marriage it was necessary to go to his
laboratory and remind him of the event that was to
take place on that day. But if Pasteur was thus guilty
of an absent-mindedness worthy of La Fontaine, he
proved as a husband so different from La Fontaine
that Madame Pasteur, when reminded of this lapse
of memory, receives the reminder with an indulgent
smile.

But to return to the laboratory : Under the same
conditions of weight, temperature, and quantity of
solvent, Pasteur placed successively, in presence of the
two acids, all the substances capable of combining
with them. In this way he obtained right-handed
and left-handed tartrates of potash, of soda, of am-
monia, of lime, and of all the oxides properly so called.
He applied himself to the compounds — and they are
numerous — which deposit themselves in liquids under
well- determined crystalline forms. Without entering
into the details of these long and patient studies, it
may be stated generally that Pasteur proved that
whatever could be done with one of the tartaric acids
could be repeated rigorously, under similar conditions,
with the other, the resultant products manifesting
constantly the same properties, with the single differ-
ence already exhibited by the two acids — that in the

FIKST DISCOVERIES. 23

one case the deviation of the plane of polarisation was
to the right, while in the other it was to the left. With
regard to all their other properties, both chemical and
physical, the identity was absolute. Solubility, simple
refraction by solutions, double refraction by crystals,
the action of heat in producing decomposition, &c.,
the similitude extended to the most perfect identity.

The Academy of Sciences, which shows by the
rarity of its reports the importance which it attaches
to them, gave for the second time an account of these
new researches. M. Biot was again the reporter. It
was with a sort of coquetry that Pasteur brought from
Strasburg perfectly labelled specimens of the magnifi-
cent crystallisations of the double series of right-
handed and left-handed tartrates. By means of
models he was able to render the forms of these
crystals visible at a distance.

M. Biot undertook to bring the subject before the
Academy. On the morning of the day when he was
to read his report he spent several hours in conversa-
tion with Pasteur. M. Biot became so excited during
the discussion that Madame Biot, with the solici-
tude peculiar to the wives of Academicians, requested
Pasteur to change the subject of conversation.

The members of the Academy shared the enthu-
siasm of M. Biot. Arago moved that the report
be inserted in the collected memoir es of the Academy.
This was an exceptional honour. Arrived for the most

24 LOUIS PASTEUK.

part at the end of their own careers, these learned men
observed with pleasure the incipient ray which had
not yet become a glory but which was the precursor
thereof.

'My young friend,' said M. Biot to Pasteur, when
presenting him to Mitscherlich somewhere about that
time, ' you may boast of having done something great,
in having discovered what had escaped such a man as
this.'

'I had studied,' replied Mitscherlich, not without
a shade of regret, addressing himself to Pasteur, ' I
had studied with so much care and perseverance, in
their smallest details, the two salts which formed the
subject of my note to the Academy, that, if you have
established what I was unable to discover, you must
have been guided to your result by a preconceived
idea.'

Mitscherlich was right, and this preconceived idea
might have been formulised thus : A dissymmetry in
the internal molecular arrangement of a chemical sub-
stance ought to manifest itself in all its external pro-
perties which are themselves capable of dissymmetry .,

If this theoretic conception was correct, Pasteur
might expect to find that all the substances in which
M. Biot had observed the power of rotating the plane of
polarisation would possess the crystalline dissymmetry

FIEST DISCOVEKIES. 25

revealed by the absence of superposability. The result
was in great part conformable to those previsions.
The substances which acted upon polarised light, as
liquids or solutions, were generally found by Pasteur
to produce dissymmetric crystals. Some of them, how-
ever, notwithstanding their power of crystallisation,
exhibited, when crystallised, no dissymmetric face.
This difficulty did not deter Pasteur. It gave him, on
the contrary, the opportunity of showing that when a
theory had in so many cases proved itself correct, an
apparent objection must not be assumed insuperable
without first sounding it to the bottom. May it not
be, he reasoned, that the absence of dissymmetry in
substances which have the molecular rotatory power
is not an accident; and may it not be possible, by
changing the conditions of the crystallisation, to make
the dissymmetry appear ?

Then, in order to modify the crystalline forms of
substances which did not show themselves to be spon-
taneously dissymmetrical, Pasteur employed a method
which had been often tried before, though its principles
could not be explained or its effects foreseen. In
imitation of Piome de Lisle, Leblanc, and Beudant, he
varied the nature of his solvents ; he introduced into
the solution, sometimes an excess of acid or of base,
sometimes foreign matters incapable of acting chemi-
cally upon those which were to be modified ; he even
employed sometimes impure mother liquids. On each

26 LOUIS PASTEUK.

occasion new facets were thus produced, and these
new facets showed the kind of dissymmetry which the
optical character demanded. Although he had to
limit his researches to those substances which, by
their ready crystallisation and the beauty of their
forms, lent themselves best to this class of proofs, the
results were so far in accord with the previsions of
theory, that no reasonable doubt could exist as to the
necessary correlation between dissymmetry and the
power to deviate polarised light.

By these researches Pasteur was led to a conclu-
sion, which is worthy of the most serious considera-
tion, regarding the difference which exists between
mineral species and artificial products on the one
side, and the organic products which can be ex-
tracted from vegetables or animals on the other. All
mineral or artificial products — for brevity let us say
all the products of inorganic nature — have a super-
posable image, and are therefore not dissymmetrical,
while vegetable and animal products — in other words,
products formed under the influence of life — have an
image not superposable ; that is to say, they are
atomically dissymmetrical, this dissymmetry express-
ing itself externally in the power of turning the
plane of polarisation. If any exceptions exist they
are more apparent than real. Pasteur himself pointed
out some of them, while demonstrating at the same

FIRST DISCOVERIES. 27"

time that it is easy to explain why all trace of dis-
symmetry disappears when substances which, like rock
crystal, have an external dissymmetry are subjected
to the process of solution.

An apparent contradiction to this law of demarca-
tion between artificial products and those of animal
and vegetable life is presented by the existence in
living creatures of substances like oxalic acid, formic
acid, urea, uric acid, creatine, &c. None of these pro-
ducts exert an action on polarised light or show any
dissymmetry in the form of their crystals. But it is
necessary to observe that these products are the result
of secondary actions. Their formation is evidently
governed by the laws which determine the constitu-
tion of the artificial products of our laboratories, or of
the mineral kingdom properly so called. In living
beings they are the products of excretion rather than
substances essential to vegetable or animal life.
When, on the other hand, we consider the most
primordial substances of vegetables and animals —
those whereof it may be justly said that they are born
under the directive influence of becoming life, such as
cellulose, fecula, albumen, fibrine, &c.— they are found
to possess the power of acting on polarised light, a
characteristic necessary and sufficient to establish
their internal dissymmetry, even when, through the
absence of crystallising power, they fail to manifest
this dissymmetry outwardly.

28 LOUIS PASTEUK.

It is, therefore, true to say that the products of
inorganic nature, whether mineral or artificial, have
never yet presented molecular dissymmetry. It may
also be affirmed that the substances which exert the
greatest influence in vital manifestations, which are
present and active in the seed and in the egg at the
moment of the marvellous start of animal and vege-
table life, all present molecular dissymmetry.

Would it be possible to indicate a more profound
distinction between the respective products of living
and of mineral nature, than the existence of this
dissymmetry on the part of the one and its absence
on the part of the other ? Is it not strange that not
one of these thousands and thousands of artificial pro-
ducts of the laboratory, the number of which is each
day augmented, should manifest either the power
of turning the plane of polarisation or non-super-
posable dissymmetry? No doubt natural dissym-
metric substances — gum, sugar, tartaric and malic
acids, quinine, strychnine, essence of turpentine,
&c.- — may be employed in forming new compounds
which remain dissymmetric, though they are artifi-
cially prepared ; but it is evident that all these new
products do but inherit the original dissymmetry of
the substances from which they are derived. When
chemical action becomes more profound, all dissym-
metry disappears, and is never seen to reappear in the
successive ulterior products.

FIRST DISCO VEEIES. 29

What can be the causes of so great a difference ?
M. Pasteur has often expressed to me the conviction
that it must be attributed to the circumstance that
the molecular forces which operate in the mineral
kingdom, and which are brought into play every day in
our laboratories, are forces of the symmetrical order ;
while the forces which are present and active at the
moment when the grain sprouts, when the egg develops,
and when, under the influence of the sun, the green
matter of the leaves decomposes the carbonic acid
of the air and utilises in divers ways the carbon of
this acid, the hydrogen of the water, and the oxygen
of these two products — are of the dissymmetric order,
probably depending on some of the grand, dissym-
metric, cosmic phenomena of our universe. While
expounding this opinion before the Academy of
Sciences, Pasteur, on one occasion, expressed himself
thus : —

* The universe is a dissymmetric whole. I am
inclined to think that life, as manifested to us, must
be a function of the dissymmetry of the universe or
of the consequences that follow in its train. The
universe is dissymmetrical; for, placing before a
mirror the group of bodies which compose the solar
system, with their proper movements, we obtain in
the mirror an image not superposable on the reality.
Even the motion of solar light is dissymmetrical. A
luminous ray never strikes in a straight line, and

30 LOUIS PASTEUK.

at rest, the leaf wherein organic matter is created
by vegetable life. Terrestrial magnetism, the oppo-
sition which exists between the north and south
poles of a magnet, the opposition presented to us by
positive and negative electricity, are all the resultants
of dissymmetric actions and motions.'

At the moment when Pasteur, entering upon the
labours which form the principal subject of this book,
abandoned the study of molecular physics and
chemistry which had previously occupied him, all
his thoughts were directed to the search of means
suited to render evident the influence of these causes
and these phenomena. At Strasburg he had procured
powerful magnets with the view of comparing the
actions of their poles, and, if possible, of introducing
by their aid, among the forms of crystals, a mani-
festation of dissymmetry. At Lille, where he was
nominated Dean of the Faculty of Sciences in 1854,
he had contrived a piece of clockwork intended to
keep a plant in continual rotary motion, first in one
direction and then in the other. * All this was gross,'
he said to me one day ; ' but, further than this, I had
proposed, with the view of influencing the vegetation
of certain plants, to invert, by means of a heliostat
and a reflecting mirror, the motion of the solar rays
which should strike them from the birth of their
earliest shoots, and in this direction there was more

FIRST DISCOVERIES. 31

to be hoped for.' He never spoke of these attempts,
because he had not had the time to follow them to
the issues of which he dreamed; but to this day
he remains persuaded that the barrier which exists
between the mineral and organic kingdoms — and
which is revealed to our eyes by the impossibility of
producing, in the reactions of the laboratory, dissym-
metric organic substances — can never be crossed until
we have succeeded in introducing among these re-
actions influences of the dissymmetric order. Accord-
ing to Pasteur, success in this direction would give
access to a new world of substances, and probably also
of organic transformations. As we have succeeded
in finding the inverse of right-handed tartaric acid,
we may hope to obtain some day all the immediate
principles inverse to those now known to us. Who
could say what vegetable and animal species would
become if it were possible to replace, in the living
cells, cellulose, albumen, and their congeners, by their
isomers with an inverse action ? Certainly the thing
is not easy, and Pasteur would be the last person to
deceive himself as to the difficulty of the problem. His
latest thought on the matter is this : — When the
attempt is made to introduce into living species pri-
mordial substances, inverse to those now existing, the
great difficulty will be to master the tendency (devenir})

1 [M. Pasteur appears to use the word devenir as a substantive
in a sense equivalent to the German Werdcnde.']

32 LOUIS PASTEUR.

proper to the species, a tendency which is potential
in the germ of each of them. In this germ, it is
to be feared, the dissymmetry of the dissymmetric
primordial substances which it embraces will always
manifest itself. Ah ! if spontaneous generation were
possible ; if we could form from mineral matter a
living cell, how much more accessible would the
problem become ! However this may be, we must
seek, by all possible means, to produce molecular
dissymmetry by the application of forces which have
a dissymmetric action. ' We must,' said Pasteur to
me on the day when, starting from the note of
Mitscherlich, he passed all these things in review,
' we must invoke the action of solenoid or helix. En-
tangled at present in labours more than sufficient to
absorb whatever of ardour and of force still remains
to me, I have no longer time to occupy myself with
these questions.' But what great things are to be
done in following out this order of ideas, and what a
route will be opened to young men possessed of that
genius of invention which is evoked so often by per-
sistent work !

This complete opposition between artificial mineral
products and vegetable and -animal ones was to Pasteur
a truth so well established that he found frequent
opportunity of affirming it under decisive circum-
stances. One day, a very skilful chemist, M. Dessaignes,

FIRST DISCOVERIES. 33

who later on became one of the correspondents of the
Academy of Sciences, announced that he had trans-
formed fumaric and malic acids into aspartic acid.
Pasteur, who some time previously had had occasion
to study these same acids, had proved that the two
first had no molecular dissymmetry — that is to say,
they exercised no optic action. In the state of so-
lution they did not turn the plane of polarised light.
Aspartic acid, on the contrary, had presented to him
molecular dissymmetry, like asparagine itself. If the
observation of M. Dessaignes were true, then bodies
which were inert in regard to polarised light, and con-
sequently non-dissymmetric, could be transformed in
the laboratory into active dissymmetric bodies. The
line of demarcation so well established would be broken.
Pasteur, whose experience regarding the note of
Mitscherlich had shown him how even the most con-
scientious observers may fail to seize upon fugitive
appearances, when unprompted to seek them by a
preconceived idea, doubted at once the accuracy of the
facts cited by M. Dessaignes. From Strasburg he
started for Vendome, where M. Dessaignes at that time
resided. M. Dessaignes immediately gave Pasteur a
small quantity of the aspartic acid which he had pre-
pared by means of fumaric and malic acids. Keturn-
ing to his laboratory, Pasteur immediately recognised
that, despite the very close resemblance of the new acid
of M. Dessaignes to that derived from asparagine,

34 LOUIS PASTEUE.

the former differed from the latter by the complete
absence in its case of molecular dissymmetry.

With regard to other facts of the same kind, an-
nounced not only in France, but in Italy, and in
England — chiefly the pretended formation of grape
tartaric acid from succinic acid, artificial and inert,
by Perkin and Duppa — Pasteur testified with absolute
certainty of judgment to the existence of phenomenal
peculiarities proper to these substances, which he had
never seen, and which had, on the other hand, been
the object of careful study by observers of great talent.

After these verifications and deductions from
theoretic views, Pasteur discovered a surprising con-
nection between the prior researches of chemistry and
crystallographic physics and the new and entirely un-
expected results of physiological chemistry. This
connection, like the thread of Ariadne, conducted him
to his recent great discoveries in medical biology.
M. Chevreul was right when, some years ago, at the
Academy of Sciences, he expressed himself thus :—

' It is by first examining in their chronological order
the researches of M. Pasteur, and then considering
them as a whole, that we are enabled to appreciate
the rigour of judgment of that learned man in form-
ing his conclusions, and the perspicacity of a mind
which, strong in the truths which it has already dis-
covered, is carried forward to the establishment of new
ones.'

FIRST DISCO VEEIES. 35

III.

Pasteur had thus established that bodies endowed
with internal dissymmetry carried this property, in
varying degrees, into their compounds or their deriva-
tives. When two of these bodies whose nature has
been revealed by the discovery of right-handed and
left-handed tartaric acid, where all is chemically iden-
tical— and which are only to be distinguished from
each other by their inverse crystallographic form, and
by their action on polarised light — enter into combina-
tion with a substance which is optically and crystallo-
graphically inert, the chemical identity ought, under
these new conditions, to be preserved. Everything
remains optically and crystallographically comparable.
The inert element adds nothing to, and takes away
nothing from, the dissymmetric faculties of the active
one.

To these curious studies Pasteur soon added a new
chapter. He reasoned thus : — If into these compounds
I introduce a substance possessing in itself the specific
properties of dissymmetry, it is evident that this sub-
stance, while entering into these combinations, must
preserve its own properties. The active substance
would, from the moment of its combination, add some-
thing to the properties of the molecular group which
-acts like itself, and subtract something from the

D 2

36 LOUIS PASTEUR.

properties of the group which acts in the opposite
manner. The resultant effect of these actions, some-
times concordant, sometimes antagonistic, would cease
to be alike in absolute quantity. And if this be the
necessary condition of similitude as to molecular
arrangement, this similitude would cease to exist, and
with its disappearance would appear all the differences
of chemical and physical properties which constitute
its outward manifestations.

The facts were found to harmonise with these
logical deductions. After having made dissymmetry
intervene as a modifier of chemical affinity, he had a
strange and manifest proof of the influence of dis-
symmetry in the phenomena of life.

It had been long known, through the observations
of a manufacturer of chemical products in Germany,
that the impure tartrate of lime of commerce, if con-
taminated with organic matters and permitted to
remain under water in summer, would ferment and
yield various products. Pasteur caused the ordinary
right-handed tartrate of ammonia to ferment in the
following manner : — He took some very pure crystalline
salt and dissolved it, adding at the same time to the
liquid some albuminoid matter, about one gramme to
100 grammes of the tartrate. The liquid placed in
a warm chamber fermented. During the process of
fermentation the liquid mass, previously limpid, be-
came gradually turbid, in consequence of the appear-

FIRST DISCOVERIES. 37

ance of a small organism which played the part of
ferment. Pasteur applied this mode of fermentation
to the paratartrate of ammonia. He saw that this
salt also fermented, depositing the same organism.
All appeared as if the course of things was the same
as in the case of the right-handed tartrate. But
Pasteur, having had the idea of following the course
of the operation with the aid of the polariscope, soon
detected a profound difference between the two fer-
mentations. In the case of the paratartrate, the
liquid, at first inert, gradually assumed a sensible
power of deviation to the left, which augmented by
degrees and attained a maximum. The fermentation
was then suspended ; there was no longer any of the
right-handed acid in the liquid, which, when evaporated
and mixed with its own volume of alcohol, immediately
furnished a beautiful crystallisation of left-handed
tartrate of ammonia.

From that moment a great new fact was esta-
blished— namely, that the molecular dissymmetry
proper to organic matters intervened in a phenomenon
of the physiological order, and did so as a modifier
of chemical affinity. The kind of dissymmetry proper
to the molecular arrangement of the left-handed
tartaric acid was, no doubt, the sole cause of the dif-
ference between this acid and the right-handed acid,
in regard to the fermentation produced by a micro-
scopic fungus. We shall see later on that organised fer-

38 LOUIS PASTEUE.

ments are almost always microscopic vegetables, which
embrace in their constitution cellulose, albumen, &c.,
identical with these same substances taken from the
higher class of vegetables and equally dissymmetric.
We can thus understand, that for the nutrition of the
ferment and the formation of its principles the
chemical changes are more easy with one of the two
tartaric acids than with the other.

The opposition of the properties of the two tartaric
acids, right and left, at the moment when the condi-
tions of life and nutrition of an organised being inter-
vened, showed themselves still more strikingly in a
very curious experiment made by Pasteur. He was the
first to prove that mildew could live and multiply on
a purely mineral soil, composed, for example, of the
phosphates of potash, of magnesia, and an ammoniacal
salt of an organic acid. For such a development of vege-
table life he employed tlie seed of penicillium glaucum,
which is to be found everywhere as common mould,
and to which he offered, as its only carbon aliment,
paratartaric acid. At the end of a little time the left-
handed tartaric acid appeared. Now this left-handed
acid could only show itself on the condition that a
rigorously equal quantity of the right-handed acid had
been decomposed. The carbon of the tartaric acid
evidently supplied to the little plant the carbon that
was necessary for the formation of its constituents and
all their organic accessories. If the microscopic seed

FIEST DISCO VEKIES. 39

of penicillium sown upon this soil was not formed of
dissymmetric elements, as is the case with all other
vegetable substances, its development, its life, its
fructification would accommodate themselves equally
well with the left-handed tartaric acid as with the
right. The fact that the left-handed tartaric acid is
less assimilable than its opposite is due solely and
evidently to the dissymmetry of one or other of the
primordial substances of the little plant.

Thus for the first time was introduced into
physiological studies and considerations the fact of
the influence of the molecular dissymmetry of natural
organic products.

Pasteur always speaks with enthusiasm of the
grand future reserved for researches which have this
influence for their object ; for molecular dissymmetry
is the only sharp line of demarcation which exists be-
tween the chemistry of inorganic and that of organic
nature.

40 LOUIS PASTEUR.

FERMENTATION.

ARRIVED at this unexpected turn in the road which
he had hitherto pursued, Pasteur paused for an in-
stant. Should he commit himself to the course which
abruptly opened before him ? His scientific instincts
urged him to do so, but the prudence and reserve
which show themselves to be the basis of his character,
whenever he finds himself called upon to make a
choice of which the necessity is not absolutely demon1
strated, held him back. Was it not wiser to continue
in the domain of molecular physics and chemistry ?
M. Biot counselled his doing so ; the route had been
made plain, success awaited him at each step, but an
incident connected with the University triumphed
over his hesitations.

He had just been nominated, at thirty-two years
of age, Dean of the Faculte des Sciences at Lille. One
of the principal industries of the Departement du Nord
is the fabrication of alcohol from beetroot and from
corn. Pasteur resolved to devote a portion of his
lectures to the study of fermentation. He felt that if

FERMENTATION. 41

he could make himself directly useful to his hearers he
would thereby excite general sympathy with, and direct
attention to the new Faculte. The young man congra-
tulated himself on this idea, and the man of science
rejoiced in it still more. He was filled by the reflec-
tions suggested to him by the strangeness of the
phenomena which he had just encountered in regard
to the molecular dissymmetry of the two tartaric acids,
in connection with the life of a microscopic organism.
He saw new light thrown upon the obscure problem
of fermentation. The part so active performed by
an infinitely small organism could not, he thought,
be an isolated fact. Behind this phenomenon must
lie some great general law.

I.

All that has lived must die, and all that is dead
must be disintegrated, dissolved or gasified ; the ele-
ments which are the substratum of life must enter
into new cycles of life. If things were otherwise, the
matter of organised beings would encumber the surface
of the earth, and the law of the perpetuity of life would
be compromised by the gradual exhaustion of its
materials. One grand phenomenon presides over this
vast work, the phenomenon of fermentation. But
this is only a word, and it suggests to the mind simply
the internal movements which all organised matter
manifests spontaneously after death, without the in-

42 LOUIS PASTEUK.

tervention of the hand of man. What is, then, the
cause of the processes of fermentation, of putrefaction,
and of slow combustion ? How is the disappearance
of the dead body or of the fallen plant to be accounted
for ? What is the explanation of the foaming of the
must in the vintage cask ? of dough, which, abandoned
to itself, rises and becomes sour ? of milk, which
curdles ? of blood, which putrefies ? of the heap of straw,
which becomes manure? of dead leaves and plants
embedded in the earth, which transform themselves
into soil ?

Many different attempts were made to account for
this mystery before science was in a condition to ap-
proach it. In our age, and at the time when Pasteur
was led to the study of the question, one theory held
almost undisputed sway. It was a very ancient theory,
to which Liebig, in reviving it, had given the weight
of his name. * The ferments,' said Liebig, ' are all
nitrogenous substances — albumen, fibrine, caseine ; or
the liquids which embrace them, milk, blood, urine —
in a state of alteration which they undergo in con-
tact with the air.'

The oxygen of the air was, according to this system,
the first cause of the molecular breaking up of the
nitrogenous substances. The molecular motions are
gradually communicated from particle to particle in
the interior of the fermentable matter, which is thus
resolved into new products.

FERMENTATION. 43

These theoretic ideas regarding the part played in
fermentation by the oxygen of the air were based upon
experiments made in the beginning of the century by
Gay-Lussac. In examining the process of Appert for
the preservation of animal and vegetable substances —
a process which consisted in inclosing these sub-
stances in hermetically sealed vessels and heating
them afterwards to a sufficiently high temperature—
Gay-Lussac had seen, for example, the must of the
grape, which had been preserved without alteration
during a whole year, caused to enter into a state of
fermentation by the simple fact of its transference to
another vessel — that is to say, by having been brought
for an instant into contact with the oxygen of the air.
The oxygen of the air appeared, then, to be theprimum
movens of fermentation.

The illustrious chemists Berzelius and Mitscherlich
explained the phenomena of fermentation otherwise.
They placed these phenomena in the obscure class
known as phenomena of contact. The ferment, in their
view, took nothing from, and added nothing to, the
fermentable matter. It was an albuminoid substance,
endowed with a force to which the name catalytic was
given. The ferment in fact acted by its mere presence.

A very curious observation, however, had been
made in France by Cagniard-Latour and in Germany
by Schwann. Cagniard-Latour, however, was the first
to publish this observation, which was destined to be-

44 LOUIS PASTEUK.

come so fruitful. One of the ferments most in use,
and known as early as the leavening of dough or the
turning of milk, is the deposit formed in beer barrels,
which is commonly called yeast. Repeating an obser-
vation of the naturalist Leuwenhoeck, Cagniard-
Latour saw this yeast, which was composed of cells,
multiplying itself by budding, and he proposed to him-
self the question whether the fermentation of sugar
was not connected with this act of cellular vegeta-
ion. But as in other fermentations the existence
of an organism had not been observed even by the
most careful search, the hypothesis of Cagniard-Latour
of a possible relation between the organisation of the
ferment and the property of being a ferment was
abandoned, though not without regret by some
physiologists. M. Dumas, for example, recognised
that in the budding of the yeast globules there must
be some clue to the phenomenon of fermentation. I,
however, repeat that as nothing of the kind had been
found elsewhere, and as all other fermentations pre-
sented the common character of requiring, to put them
in train, organic matter in a state of decomposition,
the hypothesis of Cagniard-Latour remained a simple
incident, instead of having the value of a scientific
principle.

Liebig, moreover, carrying general opinion along
with him, contended that it is not because of its
being organised that yeast is active, but because of its

FERMENTATION. 45

being in contact with air. It is the dead portion of the
yeast — that which has lived and is in the course of
alteration — which acts upon the sugar.

The new memoirs published on the subject agreed
in rejecting the hypothesis of any influence whatever
of organisation or of life in the process of fermentation.
Books, memoirs, dogmatic teaching, all were favourable
to the theoretic ideas of Liebig. If a few rare ob-
servers indicated the presence in certain fermentations
of living organisms, this presence was, in their opinion,
a purely accidental fact, which, instead of favouring
the phenomenon of fermentation, was injurious to it.

From his first investigation on lactic fermentation
Pasteur was led to take an entirely different view of
the matter. In this fermentation he recognised the
presence and the action of a living organism, which
was the ferment, just as yeast was the ferment of
alcoholic fermentation. The lactic ferment was
formed of cells, or rather of little rods nipped at
their centres, extremely small, being hardly the thou-
sandth part of a millimeter in diameter.1 It repro-
duced itself by fission — that is to say, the little rod
divided itself at its middle and formed two shorter
rods, which became elongated, nipped, in their turn,
at their centres, each giving rise, as before, to two rods.
Each of these, again, soon divided itself into two, and
so on. Why had not this been observed prior to

1 [A millimeter is ^th of an inch.]

46 LOUIS PASTEUR.

Pasteur ? For the simple reason that chemists had
never observed the production of lactic fermentation
except in complex substances. They mixed chalk
with their milk for the purpose of presew-jftg^the
neutrality of the fermenting medium. They em-
ployed substances such as caseine, gluten, animal
membranes, all of which, when examined by the
microscope, exhibited a multitude of mineral or
organic granules, with which the lactic ferment was
confounded. Thus the first care of Pasteur, with tfpp
view of proving the presence of the ferment and its
life, was to replace the cheesy matter and all its
congeners by a soluble, nitrogenous body, which would
permit of the microscopic examination of all the living
cellular products.

In a memoir presented to the Aqademy of Sciences
in 1857 Pasteur stated that there were * cases where
it is possible to recognise in lactic fermentation, as
practised by chemists and manufacturers, above the
deposit of chalk and the nitrogenous matter, a grey
substance which forms a zone on the surface of the
deposit. Its examination by the microscope hardly
permits of its being distinguished from the disinte-
grated caseum or gluten which has served to start the
fermentation. So that nothing indicates that it is a
special kind of matter which had its birth during the
fermentation. It is this, nevertheless, which plays the
principal part.'

FERMENTATION. 47

To isolate this substance and to prepare it in a
state of purity, Pasteur boiled a little yeast with from
fifteen to twenty times its weight of water. He then
carefully filtered the liquid, dissolved in it about fifty
grammes of sugar to the litre, and added to it some
chalk. Taking then, by means of a drawn-out tube,
from a good ordinary lactic fermentation a trace of
the grey matter of which we have just spoken, he
placed it as the seed of the ferment in the limpid
saccharine solution. By the next day a lively and
regular fermentation had set in, the liquid becoming
turbid and the chalk disappearing, and one could
distinguish a deposit which progressed continually
as the chalk dissolved. This deposit was the lactic
ferment.

Pasteur reproduced this experiment by substituting
for the water of the yeast a clear decoction of nitro-
genous plastic substances. The ferment invariably
presented the same aspect and the same multiplica-
tion. These results, however, did not yet satisfy
Pasteur. He desired more rigour in a subject of such
theoretic importance. Might not the partisans of
Liebig's theory argue, if not without subtlety yet
with a semblance of justice, that the fermentation
was not due to the formation and progressive growth
of this feeble nitrogenous globular deposit, but rather
to the nitrogenous matter dissolved during the decoc-
tion of the yeast used in the composition of the

48 LOUIS PASTEUK.

liquor ? Up to a certain point it might be maintained
that the dissolved matters which had been in contact
with the oxygen of the air had been thrown into mole-
cular motion, that this motion had been communicated
to the fermentable matter, and that the deposit of the
pretended organised ferment was but an accident —
one of the physical changes or one of the precipitates
so frequently observed in the modifications of albumi-
noid matters. In the observation of Cagniard-Latour
and of Schwann as to the life of the yeast, Liebig
saw nothing more. ' One cannot deny,' said he, ' the
organisation of the yeast or its multiplication by bud-
ing, but these living cells are always associated with
other dead cells in process of molecular alteration.
It is these molecular motions which communicate
themselves to the molecules of the sugar, break them
up, and cause them to ferment.'

The arguments of Liebig derived great strength
from the belief which was shared by all chemists
that the cells of yeast perish during fermentation
and form lactate of ammonia. On examining this
assertion, Pasteur found that not only was there no
ammonia formed during alcoholic fermentation, but
that even if ammonia were added it disappeared, en-
tering into the formation of new yeast cells. Was not
this a proof of the potency of the organised ferment ?

Tormented, however, by the idea that, notwith-
standing all these facts, the reasonings of Liebig

FERMENTATION. 49

might still find some credit, Pasteur worked earnestly
to discover new facts capable of demonstrating that
Liebig's theory was absolutely false. He made two
crucial experiments, the one relating to the yeast of
beer, or of alcohol, and the other relating to the lactic
ferment. He introduced into a pure solution of sugar
a small quantity of crystallisable salt of ammonia,
then some phosphates of potash and magnesia, and
he sowed in this medium an imponderable quantity,
if we may so express it, of fresh cells of yeast. The
cells thus sown multiplied, and the sugar fermented.
In other words, the phosphorus, the potassium, the
magnesium of the mineral salts, united to form the
substances which compose the ferment. By this ex-
periment, so simple and yet so demonstrative, the
power of the organisation of the ferment was once
for all established. The contact theory of Berzelius
had no longer any meaning, since it was evident that
the fermentable matter here furnished to the ferment
one of its essential elements, namely, carbon. Liebig's
theory of communicated molecular motion, originating
in a nitrogenous albuminoid substance, had no better
claim, since such substances had been discarded. The
whole process took place between the sugar and a
ferment germ which owed its life and development to
nutritive matters, the most important of which was
the fermentable substance. Fermentation, in short,
was simply a phenomenon of nutrition. The ferment

£

50 LOUIS PASTEUR.

augmented in weight, feeding upon the sugar, and its
vitality was such that it contrived to build up the
complex materials of its own organisation by means
of sugar and purely mineral elements.

In a second experiment, Pasteur demonstrated
that, notwithstanding their smallness and the pos-
sibility of confounding them with the amorphous
granules of caseine and gluten, the little particles of
lactic ferment were indeed alive, and that they, and
they only, were the cause of lactic fermentation. He
mixed with some water, sweetened with sugar, a small
quantity of a salt of ammonia, some alkaline and
earthy phosphates, and some pure carbonate of lime
obtained by precipitation. At the end of twenty-four
hours the liquid began to get turbid and to give off
gas. The fermentation continued for some days.
The ammonia disappeared, leaving a deposit of phos-
phates and calcareous salt. Some lactate of lime was
formed, and at the same time one could notice the
deposition of the little lactic ferment. The germs of
the lactic ferment had, in this case, been derived from
particles of dust adhering to the substances themselves,
of which the mixtures were made, or to the vessels
used, or from the surrounding air. The chapter on
spontaneous generation will render this clear.

It suffices here to state that the results of this
second experiment were absolutely conclusive, and
that the theories of contact force or of communicated

FERMENTATION. 5l

motion, which up to that time had reigned in science,
were completely overthrown.

II.

The light shed by these experiments quickly ex-
tended its sphere ; and Pasteur lost no time in dis-
covering a new ferment, that of butyric acid. Having
shown the absolute independence which exists between
the ferment of butyric acid and the others, he found,
contrary to the general belief, that the lactic ferment is
incapable of giving rise to butyric acid, and that there
exists a butyric fermentation having its own special
ferment. This ferment consists of a species of vibrio.
Little transparent cylindrical rods, rounded at their ex-
tremities, isolated or united in chains of two or three, or
sometimes even more, form these vibrios. They move by
gliding, the body straight, or bending and undulating.
They reproduce themselves by fission, and to this mode
of generation their frequent arrangement in the form
of a chain is due.

Sometimes one of the little rods, with a train of
others behind it, agitates itself in a lively manner as if
to detach itself from the rest. Often, also, the little
rod, after being broken off, holds on still to its chain
by a mucous transparent thread.

These little infusoriae may be sown like the yeast
of beer or the lactic ferment. If the medium in

52 LOUIS PASTEUE.

which they are sown is suitable for their nourishment,
they will multiply to infinity ; but the character most
essential to be observed is, that they may be sown in a
liquid which contains only ammonia and crystallisable
substances, together with the fermentable substances,
sugar, lactic acid, gum, &c. The butyric fermentation
manifests itself as these little organisms multiply.
Their weight sensibly increases, though it is always
minute in comparison with the quantity of butyric
acid produced ; this is found to be the case in all
other fermentations.

This experiment no doubt resembles those made
with the alcoholic and lactic ferments. But it is dis-
tinguished from them by one circumstance eminently
worthy of attention. The butyric ferment, by its
motions and by its mode of generation, furnishes the
irrefutable proof of its organisation and of its life.
This ferment, moreover, presented to Pasteur a new
and unexpected peculiarity. The vibrios live and
multiply without the smallest supply of air or of free
oxygen. Not only, indeed, do they live without air,
but the air destroys them and arrests the fermentation
which they initiate. If a current of pure carbonic
acid is made to pass into the liquid where they are
multiplying, their life and reproduction do not appear
to be at all affected by it. If, on the contrary, instead
of the current of carbonic acid we employ one of
atmospheric air for only one or two hours, the vibrios

FEEMENTATION. 53

fall without movement to the bottom of the vessel, and
the butyric fermentation which was dependent on their
existence is immediately arrested.

Pasteur designated this new class of organisms by
the 'name of anaerobies ; that is to say, beings which
can live without air. He reserves the designation
aerobics for all the other microscopic beings which, like
the larger animals, cannot live without free oxygen.
* It matters little,' added Pasteur, ' whether the pro-
gress of science makes of this vibrio a plant or an
animal ; it is a living organism, endowed with motion,
which is a ferment and which lives without air.'

In meditating upon these facts, and upon the
general character of fermentation, Pasteur* soon found
himself in a position to approach more nearly to the
essential nature of these mysterious phenomena. In
what way do microscopic organisms provoke the phe-
nomena of fermentation ?

The organism eats, if one may say so, one part of
the fermentable matter. But how does this phenome-
non of nutrition differ so much from that of higher
beings ? In general, for a given weight of nutritive
matter which the animal takes in, it assimilates a
quantity of the same order. In fermentation, on the
contrary, the ferment, while nourishing itself with
fermentable matter, decomposes a quantity great in
comparison to its own individual weight. Again, the

54 LOUIS PASTEUE.

butyric ferment lives without free oxygen. Is there
not, said Pasteur, a hidden relation between the
property of being a ferment and the faculty of living
without free oxygen? Are not vibrios which impera-
tively require for their nutrition and multiplication the
presence of oxygen gas those which will never have the
properties of ferments ?

Pasteur then contrived a series of experiments with
the view of placing in parallelism these two curious
physiological facts : life without air and the charac-
teristics of ferments.

We know how wine and beer are prepared. The
must of grapes and the must of beer are placed in
wooden vats, or in barrels of greater or less dimen-
sions. Whether the fermentation proceeds from germs
taken from the exterior surface of the grapes, or
from a small quantity of ferment sown in the must
under the form of yeast, as in the fermentation of
beer, the life of the ferment, its multiplication, the
augmentation of its weight, are so many vital actions
which to a certainty cannot borrow from the free
oxygen of the external air, or from that originally
dissolved in the must, an appreciable quantity of this
gas. All the life of the cells of the ferment which
multiplies itself indefinitely appears then to take place
apart from free oxygen gas. In certain breweries
in England the fermenting vats have sometimes a
capacity of several thousands of hectolitres ; and the

FERMENTATION. 55

fermentation liberates pure carbonic acid, a gas much
heavier than atmospheric air, which rests on the
surface of the liquid in the vat in a layer thick enough
to protect the liquid underneath from any contact with
the external air. All this liquid mass, then, is inclosed
between the wooden sides of the vat and a deep layer
of heavy gas which contains no trace of free oxygen.
In this liquid, nevertheless, the life of the cells of the
ferment and the production of all its constituents go
on for several days with extraordinary activity. Here
certainly we have life without air, and the ferment
character expresses itself in the enormous difference
between the weight of the ferment formed and collected
from the vats under the name of yeast, at the end
of the operation, and the weight of the sugar which
has fermented, transforming itself into alcohol, car-
bonic acid, and various other products.

Pasteur has studied experimentally that which
takes place when, without otherwise changing the
conditions of these phenomena, the arrangement
is so modified as to permit the introduction of the
free oxygen of the atmosphere. It sufficed for this
purpose to provoke a fermentation of the must of
beer, or the must of grapes, upon shallow glass dishes
presenting a large surface, or in a flat-bottomed
wooden trough with sides a few centimeters in height,
instead of in deep vats as before. In these new con-
ditions the ferinentation manifests an activity even

56 LOUIS PASTEUB.

more extraordinary than it did in the deep vats. The
life of the ferment is itself singularly enhanced, but
the proportion of the weight of the decomposed sugar
to that of the yeast formed is absolutely different in
the two cases. While, for example, in the deep vats,
a kilogram of ferment sometimes decomposes seventy,
eighty, one hundred, or even one hundred and fifty
kilograms of sugar, in the shallow troughs one kilo-
gram of the ferment will be found to correspond to
only five or six kilograms of decomposed sugar. These
proportions between the weight of the sugar which
ferments and the weight of the ferment produced,
constitute the measure of what one might call the
ferment's character — of that character which distin-
guishes its mode of life from that of all other existences,
great or small, in which the weight of the organising
matter and the assimilated alimentary matter are about
equal. In other words, the more free oxygen the yeast
ferment consumes, the less is its power as a ferment.
Such is the case in the shallow troughs where the
extended surface is exposed to the contact of the
oxygen of the air. The more, on the contrary, the
life of the ferment is carried on without the presence of
free oxygen, the greater is its power of decomposing and
of fermenting the saccharine matter. This is the case
in deep casks. The intimate co-relation then between
life without air and fermentation appears complete.
The unexpected light which these facts threw upon

FERMENTATION. 57

the cause of the phenomena of fermentation made a
forcible impression upon all thinking minds. * In
these infinitely small organisms,' M. Dumas said one
day to M. Pasteur before the Academy of Sciences,
' you have discovered a third kingdom. — the kingdom
to which those organisms belong which, with all the
prerogatives of animal life, do not require air for their
existence, and which find the heat that is necessary
for them in the chemical decompositions which they
set up around them.'

The work of Pasteur, demonstrating that fermen-
tation was always dependent on the life of a micro-
scopic organism, continued without interruption. One
of the most remarkable of his researches is that
which relates to the fermentation of the tartrate of
lime. The demonstration of life and of fermentation
without free oxygen is in this paper carried to
the utmost limits of experimental rigour and pre-
cision.

III.

But there is still another class of chemical pheno-
mena where the life without air of microscopic or-
ganisms is fully shown. Pasteur proved that in the
special fermentation which bears the name of putre-
faction the primum movens of the putrefaction resides
in microscopic vibrios of absolutely the same order
as those which compose the butyric ferment. The

58 LOUIS PASTEUE.

fermentation of sugar, of mannite, of gums, of lactate
of lime, by the butyric vibrio, so closely resembles the
phenomena of putrefaction, that one might call these
fermentations the putrefaction of sugar and of the
other products.

If it has been thought right to call the fermenta-
tion of animal matters putrefaction, it is because at the
moment of the decomposition of fibrine, of albumen,
of blood, of gelatine, of the substance of the tendons,
&c., the sulphur, and even the phosphorus*, which
enter into their composition give rise to putrid odours,
due to the evil-smelling gases of sulphur and phos-
phorus.

The phenomena of putrefaction being then simply
fermentations, differing only in regard to the chemical
composition of the fermenting matters, Liebig natu-
rally included them in his general theory of the de-
composition of organic matters after death. At a
period long antecedent to Pasteur's labours it had
been established that there existed in putrefying
matters fungi or microscopic animalcules, and the idea
had taken shape that these creatures might have an
influence in the phenomena. The proofs were want-
ing, but the notion of a possible relation remained.
We may read in his * Lessons on Chemistry ' with
what disdain M Liebig mentioned these hypothetical
opinions.

1 Those who pretend to explain the putrefaction

IEEMENTATION. 59

of animal substances by the presence of animalculse/
lie wrote, ' reason very much like a child who would
explain the rapidity of the Ehine by attributing it
to the violent motions imparted to it in the direc-
tion of Bingen by the numerous wheels of the mills
of Mayence. Is it possible to consider plants and
animals as the causes of the destruction of other
organisms when their own elements are condemned to
undergo the same decompositions as the creatures
which have preceded them? If the fungus is the
cause of the destruction of the oak, if the microscopic
animalcula is the cause of the putrefaction of the
dead elephant, I would ask in my turn what is the
cause which determines the putrefaction of the fungus
or of the microscopic animalcula when life is with-
drawn from these two organisms ? '

Thirty-two years later, and after Pasteur had
accumulated, during more than twenty years, proof
upon proof that the theory of Liebig would not stand
examination, a physician of Paris, M. Bouillaud, asked,
with the insistent voice of a querulous octogenarian :
* Let M. Pasteur then tell us here, in presence of the
Academie de Medecine, what are the ferments of the
ferments.'

Before replying to this argument, which Liebig
and M. Bouillaud believed to be irrefutable, Pasteur,
wishing to mark all the phases of the phenomena,
expounded in a short preamble the part played by

60 LOUIS PASTEUE.

atmospheric oxygen in the destruction of animal and
vegetable matters after death. It is easy to under-
stand, indeed, that fermentation and putrefaction only
represent the first phase of the return to the atmo-
sphere and to the soil of all that has lived. Fermenta-
tions and putrefactions give rise to substances which
are still very complex, although they represent the
products of decomposition of fermentable matters.
When sugar ferments, a large proportion of it becomes
gas ; but alongside of the carbonic acid gas which
is formed, and which is, indeed, a partial return of
the sugar to the atmosphere, new substances, such
as alcohol, succinic acid, glycerine, and materials of
yeast, are produced. When the flesh of animals
putrifies, certain products of decomposition, also very
complex, are formed with the vapour of water and
the other gases of putrefaction. Where, then, does
nature find the agents of destruction of these secondary
products ?

The great fact of the destruction of animal and
vegetable matters is accomplished by slow combustion,
through the appropriation of atmospheric oxygen.
Here, again, one must banish from science the pre-
conceived views which assumed that the oxygen seized
directly on the organic matter after death, and that
this matter was consumed by purely chemical pro-
cesses. It is life that presides over this work of death.

If fermentation and putrefaction are principally

FERMENTATION. 61

the work of microscopic anaerobies, living without free
oxygen, the slow combustion is found very largely, if
not exclusively, to depend upon a class of infinitely
small aerobies. It is these last which have the pro-
perty of consuming the oxygen of the air. It is these
lower organisms which are the powerful agents in
the return to the atmosphere of all which has lived.
Mildew, mould, bacteria, which we have already
noticed, monads, two thousand of which would go to
make up a millimeter, all these microscopic organisms
are charged with the great work of re-establishing the
equilibrium of life by giving back to it all that it
has formed.

To demonstrate the important part played every-
where by these microscopic organisms, Pasteur made
two experiments. He first introduced into vessels air
deprived of all dust. This process we shall have occa-
sion to examine in all its details, in connection with
the researches on spontaneous generation. In these
vessels, containing pure air, were placed the water of
yeast with sugar dissolved in it, milk, sawdust — all
of which had been deprived by heat of the germs of
the lower organisms. The vessels and their contents
were then subjected to a temperature of twenty-
five to thirty-five degrees Centigrade. In a series
of parallel experiments, made under the same con-
ditions and at the same temperature, Pasteur took
no steps to prevent the germination of the little seeds

62 .LOUIS PASTEUE.

of mould suspended in the air, or associated with the
substances contained in the vessels, neither did he
avoid other infinitely small germs of the class
aerobics.

After some time the air of all the vessels of the
two series was submitted to analysis, when, behold, a
very interesting fact ! In the vessels where life had
been withdrawn from the organic matters — that is
to say, where there were no germs — the air still con-
tained a large proportion of oxygen. In the vessels,
on the contrary, where the microscopic organisms
had been allowed to develop, the oxygen was totally
absent, having been replaced by carbonic acid gas.
And, further, for this absorption and total consumption
of the oxygen gas a few days had sufficed ; while in the
vessels without microscopic life there remained, after
several years, a considerable quantity of oxygen in a
free state, so weak is the proportion of oxygen that
the organic matters consume directly and chemically
when the infinitely small organisms are absent.

But can these microscopic organisms, after having
decomposed or burnt up all these secondary products,
be in their turn decomposed ?

How, cried M. Bouillaud, repeating his question,
can they be destroyed or decomposed? How can
their materials, which are of the same order as those
of all the living creatures of the earth, be gasified and
caused to return to the atmosphere ? After having

FEKMENTATION. 63

been charged with the transformation of others, whose
business will it be to transform them ?

A ferment which has finished its work, replied
Pasteur, and which for want of aliment cannot con-
tinue it, becomes in its turn an accumulation, so to
speak, of dead organic matters. Such,' for example,
would be an accumulation of yeast exposed to the air.
Leave this mass to itself in summer temperature, and
you will see appear in the interior of the mass ana-
erotic vibrios and the putrefactions associated with
their life when protected from contact with the air. At
the same time, on the surface of the entire mass — that
is to say, that which finds itself in immediate contact
with the oxygen of the air — the germs of bacteria, the
seeds of mould will grow, and, by fixing the oxygen,
determine the slow combustions which gasify the mass.
The ferments of ferments are simply ferments. As
long as the aerobic ferments of the surface have at
their disposal free oxygen, they will multiply and con-
tinue their work of destruction. The anaerobic vibrios
perish for want of new matter to decompose, and they
form, in their turn, a mass of organic matter which, by
and by, becomes the prey of aerobies. The portion of
the aerobies which has lived becomes the prey either
of new aerobies of different species, or of individuals
of their own species, so that from putrefaction to
putrefaction, and from combustion to combustion, the
organic mass with which we started finds itself reduced

64 LOUIS PASTEUR.

to an assemblage of anaerobic and aerobic germs — of
those same germs which were mixed up in the original
primitive organic substances.

Though a collection of germs becomes again in its
turn a collection of organic matter, subject to the
double action of the phenomena 'of putrefaction and
of combustion, there need be no anxiety as to their
ultimate destruction ; in the final analysis they repre-
sent life under its eternal form, for life is the germ,
and the germ is life.

Thus in the destruction of that which has lived,
all reduces itself to the simultaneous action of these
three great natural phenomena — fermentation, putre-
faction, and slow combustion. A living organism
dies — animal, or plant, or the remains of one or the
other. It is exposed to the contact of the air. • To the
life which has quitted it succeeds life under other
forms. In the superficial parts, which the air can
reach, the germs of the infinitely small aerobies hatch
and multiply themselves. The carbon, the hydrogen,
and the nitrogen of the organic matters are trans-
formed by the oxygen of the air, and under the in-
fluence of the life of these aerobies, into carbonic
acid, vapour of water, and ammonia gas. As long as
organic matter and air are present, ihese combustions
will continue. While these superficial combustions
are going on, fermentation and putrefaction are doing

FERMENTATION. 65

their work in the interior of the mass by the developed
germs of the anaerobies, which not only do not require
oxygen for their life, but which oxygen actually kills.
Little by little, at length, by this work of fermentation
and slow combustion, the phenomenon is accomplished.
Whether in the free atmosphere, or under the earth,
which is always more or less impregnated with air, all
animal and vegetable matters end by disappearing.
To arrest these phenomena an extremely low tem-
perature is required. It is thus that in the ice of the
Polar regions antediluvian elephants have been found
perfectly intact. The microscopic organisms could not
live in so cold a temperature. These facts still further
strengthen all the new ideas as to the important part
performed by these infinitely small organisms, which
are, in fact, the masters of the world. If we could
suppress their work, which is always going on, the
surface of the globe, encumbered with organic matters,
would soon become uninhabitable.

66 LOUIS PASTEUR.

ACETIC FERMENTATION.

THE MANUFACTURE OF VINEGAR.

SOON afterwards Pasteur came upon a most curious
illustration of the ' fixation ' of atmospheric oxygen by
a microscopic organism — the transformation of wine
into vinegar. As its name indicates, vinegar is
nothing else than wine turned sour. Everybody
has remarked that wine, left to itself, in circum-
stances which occur daily, is frequently transformed
into vinegar. This is noticed more particularly
when bottles, having been uncorked, are left in a
half- empty condition. Sometimes, however, wine
turns sour even in corked bottles. In this case
we may be sure that the bottles have been standing
upright, and that corks more or less defective have
permitted the air to penetrate into the wine. The
presence of air, in fact, is indispensable to the chemical
act of transforming wine into vinegar. How does this
air intervene ? And what is the little microscopic
creature which, in conjunction with the air, becomes
the agent of this fermentation ?

ACETIC FERMENTATION. 67

In a celebrated lecture given at Orleans at the
request of the manufacturers of vinegar in that town,
Pasteur, after having stated the two foregoing scien-
tific questions, proceeded to examine the difference
between wine and vinegar. What takes place in the
fermentation of the juice of the grape which yields the
wine ? The sugar of this juice disappears, giving
place to carbonic acid gas, which is exhaled during
fermentation, and to alcohol, which remains in the
fermented liquid. Formerly, chemists gave the name
of ' spirit ' to all volatile matters which could be
collected from distillation. Now, when we distil wine
and condense the vapour in a worm surrounded by
cold water, we collect the spirit of wine at the ex-
tremity of the worm — this, when the water with
which it is mixed during distillation is withdrawn from
it, we designate by the name of alcohol. Vinegar
contains no alcohol. When distilled it yields water
and a spirit. But this spirit is acid, with a very
pungent odour, and not inflammable like spirit of
wine. Separated from the water which had accom-
panied it during the distillation, this spirit takes the
name of acetic acid. This is the form in which it is
used in smelling bottles — in those bottles of English
salts the vapour of which is so penetrating.

In the formation of vinegar in contact with air
the alcohol disappears, and is replaced by acetic acid.
The air has thus given up something to the wine.

F 2

68 LOUIS PASTEUE.

Atmospheric air every one knows to be a mixture
of nitrogen and oxygen, the nitrogen in the proportion
of four-fifths of the total volume, and the oxygen of
one-fifth. Well, in the transformation of wine into
vinegar the nitrogen remains inactive. It is the
oxygen alone which enters into combination with the
alcohol. You ask for the proof of this ? Take a
bottle of wine turned sour, a bottle which at the same
time is stopped hermetically ; if the oxygen of the air
contained in the bottle has combined with the alcohol,
then, instead of air, there will be nothing in the bottle
but nitrogen gas. Turn the bottle upside down and
open it in a basin of water. The water of the basin
will rush into the bottle to fill the partial vacuum
ereated by the disappearance of the oxygen. The
volume of water which enters the bottle is precisely
equal to a fifth part of the total original volume of
the air which the bottle contained at the time when
it was closed. Moreover, it is easy to show that the
gas which remains in the bottle has the properties of
nitrogen gas. A lighted match is extinguished in it
as if plunged into water, and a bird dies immediately
in it of asphyxia.

If we confine our knowledge to what has gone
before, it would seem that alcohol diluted with water
and exposed to the air ought to furnish acetic acid.
It is not so, however. Pure water alcoholised to the
degree of ordinary wines may remain for whole years

ACETIC FERMENTATION. 69

in contact with the air, without the least acetifica-
tion. In this difference between natural wine and pure
water alcoholised, and exposed to contact with air, we
touch upon a vital point in the phenomena of fermen-
tation. The celebrated theory of Liebig, which Pas-
teur was destined to overthrow, might be thus summed
up : — If pure alcoholised water cannot become sour in
contact with air, as is the case with wine, it is because
the pure alcoholised water lacks the albuminoid sub-
stance which exists in the wine in a state of chemical
alteration, and which is a ferment capable of causing
the oxygen of the air to combine with the alcohol.
And the proof, according to Liebig, that things act
rigorously thus is, that if you add to the mixture of
water and alcohol a little flour, or a little meat-juice,
or even a minute quantity of any vegetable juice,
the acetic fermentation arises, as if by compulsion.
In other words, by the addition of a small quantity
of any nitrogenised substance in process of alteration,
you cause the union of the oxygen of the air with the
alcohol.

There is doubtless always in the wine, when it
turns sour, a necessary intermediary, producing the
fixation of the oxygen of the air ; since in no circum-
stances can pure alcohol, diluted to any degree what-
ever with pure water, transform itself into vinegar.
But this necessary intermediary is not, as the German
theory would have it, a dead albuminoid substance ;

70 LOUIS PASTEUK.

it is a plant, and of all plants one of the simplest and
most minute, which has been known from time imme-
morial under the name of flower of vinegar. This
little fungus is invariably present on the surface of
a wine which is being transformed into vinegar.
Liebig was not ignorant of this, but he regarded it as
a simple coincidence. Do we not know, said he, that
whenever an infusion of organic matter is exposed to
the air it becomes covered with a cryptogam ic vege-
tation, or is invaded by a crowd of aninialculae ? Is
not vinegar a vegetable infusion ? Vinegar affords a
refuge to the flower of vinegar, just as it gives refuge
to what are called the little eels of vinegar.

We can appreciate here the uncertainties of pure
observation. The great art — and no one practised it
better than Pasteur — consists in instituting decisive
experiments which leave no room for an inexact inter-
pretation of facts. These decisive proofs of the true
part played by the little microscopic fungus, by this
flower of vinegar, this mycoderrna aceti, are thus
formulated by Pasteur. It is but another example
of the method which he used in alcoholic, lactic, and
tartaric fermentations. The theories of Berzelius, of
Mitscherlich, and of Liebig were destined again to
receive the rudest shocks by the demonstration of these
rigorous facts.

Let us place a little wine in a bottle, then her-
metically seal it, and leave it to itself. In these

ACETIC FERMENTATION. 71

conditions the wine becomes sour. But if we take
the precaution of putting the bottle into hot water, so
that the wine and the air in the bottle may be heated
for some instants to a temperature of 60° Centigrade,
and if, after cooling, we leave the bottle to itself,
the wine in these conditions will never become trans-
formed into vinegar. The heating, however, must
have left intact the albuminoid or nitrogenous sub-
stances contained in the wine. These, then, cannot
constitute the ferment of the vinegar. Can it be
maintained that by heating the wine to 60° we have
altered the albuminoid matter, which is, on this
account, no longer able to act as a ferment, or, in other
words, no longer able to determine the union of the
oxygen of the air with the alcohol ? This hypo-
thesis falls to pieces before the following experiment.
Open the bottle, blow into it with bellows, so that
the once heated wine shall come into contact with
ordinary air, and the acetification of the wine will take
place.

But the master experiment is the following. We
have seen that pure alcoholised water never turns sour
unless some albuminoid matter is introduced into it.
Pasteur saw that this albuminoid matter might be
completely suppressed and replaced by saline crystal-
Usable substances, alkaline and earthy phosphates, to
which has been added a little phosphate of ammonia.
In these conditions, especially if the alcoholised water

72 LOUIS PASTEUR.

be acidulated by small quantities of pure acetic acid,
one actually sees the mycoderm developing, and the
alcohol transforming itself into acetic acid. It is
not possible to demonstrate in a more convincing
manner that the albuminoid matters of the wine are
not in this case the acetic ferment. These albuminoid
matters, however, contribute to the acetic fermenta-
tion, but only as being an aliment to the mycoderma
aceti, and notably a nitrogenous aliment. The true
and only ferment of vinegar is the little fungus; it
is the great agent of the phenomenon; it, indeed,
accomplishes all.

Is there not a great charm in seeing an obscure
subject clearly illuminated by facts well understood
and well interpreted ? If in a bottle containing wine
and air and raised to a temperature of 50° or 60°
the wine never turns sour, it is because the germs
of the mycoderma aceti, which the wine and the
air hold in suspension, are deprived of all vitality
by the heat. Placed, however, in contact with ordi-
nary air, this once-heated wine can turn sour ; because,
though the germs of the mycoderma aceti contained
at first in the wine are killed, this is not the case
with those derived from the surrounding air. Pure
alcoholised water never turns sour, even in contact
with ordinary air, and with whatever germs this air
may carry, or that may be found in the dust of the
vessels which receive it. The reason is that these

ACETIC FEKMENTATION. 73

germs cannot become fertile because of the absence of
their indispensable food. Wine in bottles well filled
and laid flat do not acetify ; this is because the myco-
derm cannot multiply for lack of oxygen. Without
doubt the air constantly penetrates through the pores
of the cork, but always in such feeble quantities that
the colouring matters of the wine, and other more or
less oxydisable constituents, take possession of it with-
out leaving the smallest quantity for the germs of the
mycoderm which are generally suspended in the
wine. When the bottle is upright the conditions are
quite altered. The desiccation of the cork renders it
much more permeable to the air, and the germs of
the mycoderm on the surface of the liquid, if any
exist there, are enveloped by air.

Thus, to recapitulate in a few words the principles
which have just been established ; it is easy to see that
the formation of vinegar is always preceded by the de-
velopment, on the surface of the wine, of a little plant
formed of strangulated particles, of an extreme tenuity,
and the accumulation of which sometimes takes the
form of a hardly visible veil, sometimes of a wrinkled
film of very slight thickness, and greasy to the touch,
because of the various fatty matters which the plant
contains.

This cryptogam has the singular property of con-
densing considerable quantities of oxygen and of pro-
voking iln.Q fixation of this gas upon the alcohol, which

74 LOUIS PASTEUR.

is thereby transformed into acetic acid. The little
mycoderm is not less exacting than larger vegetables.
It must have its appropriate aliments. Wine offers
them in abundance : nitrogenous matters, the phos-
phates of magnesia and of potash. The mycoderm
thrives, moreover, in warm climates. To cultivate
it in temperate regions like ours it is well to warm
artificially the places where it is cultivated. But if
wine contains within itself all the elements necessary
to the life of the little mycoderm, this life is further
promoted by rendering the wine more acid through
the addition of acetic acid.

What, then, can be more simple than to produce
vinegar from wine — a manufacture which justly makes
the reputation of the town of Orleans ? Take some
wine, and after having mixed with it one-fourth or
one-third of its volume of vinegar already formed,
sow on its surface the little plant which does the work
of acetification. It is only necessary to skim off, by
means of a wooden spatula, a little of the mycodermic
film from a liquid covered with it, and to transfer it
to the liquid to be acetified. The fatty matters which
it contains render the wetting of it difficult. Thus,
when we plunge into the liquid the spatula covered
with the film, the latter detaches itself and spreads
out over the surface instead of falling to the bottom.
When we operate in summer, or in a room heated to
15° or 25° Centigrade in winter, in twenty-four or

ACETIC FERMENTATION. 75

forty-eight hours at most, the mycoderm covers the
whole liquid, so easy and rapid is its development.
After some days all the wine has become vinegar.

On one occasion, in a discussion which he was hold-
ing at the Academy of Sciences, Pasteur, wishing to
affirm the prodigious activity of the life and multipli-
cation of this little organism, expressed himself thus : —

' I would undertake in the space of twenty-four
hours to cover with niycoderma aceti a surface of
vinous liquid as large as the hall in which we are
here assembled. I should only have to sow in it the
day before almost invisible particles of newly-formed
mycoderma aceti.'

Let the reader try to imagine the millions upon
millions of little mycoderma particles which would
come to life in that one day.

But how is the mycoderm seed to be obtained in the
first instance ? Nothing more simple. The mycoderma
aceti is one of those little so-called ' spontaneous ' pro-
ductions which are sure to appear of themselves on the
surface of liquids or infusions suitable to their develop-
ment. In wine, in vinegar, or suspended in air, every-
where around us, in our towns, in our houses, there
exist germs of this little plant. If we wish to procure
some fresh mycoderm it is only necessary to put a
mixture of wine and vinegar into a warm place. In
a few days, generally, if not always, there appear here
and there little greyish patches scattering the light

76 LOUIS PASTEUE.

instead of regularly reflecting it, as does the surround-
ing liquid. These specks go on increasing progres-
sively and rapidly. This is the mycoderma aceti
raised from the seeds .which the wine or the added
vinegar contained, or which the air deposited ; just as
we see a field covered with divers weeds by seeds natu-
rally distributed in the earth, or which have been
brought to it by the wind or by animals. Even in
this last circumstance the comparison holds good, for
after you have put wine or vinegar in a warm place
there soon appear, whence we know not, little reddish
flies, so commonly seen in vinegar manufactories, and
in all places where vegetable matter is turning sour.
With their feet, or with their probosces, these flies
transport the seed.

At Orleans the process for the manufacture of
vinegar is very simple. Barrels ranged over each
other have on each of their vertically-placed bottoms
a circular opening some centimeters in diameter, and
a smaller hole adjacent, called fausset, for the air to
pass in and out when the large opening is closed,
either by the funnel, through which the wine is intro-
duced, or by the syphon, which is used for draw-
ing off the vinegar. These barrels, of which the
capacity is 230 litres, are half filled. The manual
labour consists in keeping up a suitable temperature
in the vessel, and in drawing from it every eight days

ACETIC FERMENTATION. 77

about eight or ten litres of vinegar, which are replaced
by eight or ten litres of wine.

A barrel in which this give-and-take of wine and
vinegar goes on is technically called a * mother.' The
starting of a 'mother' is not a rapid process. We
begin by introducing into the barrel 100 litres of very
good and very limpid vinegar ; then two litres only of
wine are added. Eight days after, three litres of wine
are added, a week later four or five, until the barrel
contains about 180 to 200 litres. Then for the first
time vinegar is drawn off in sufficient quantity to
bring back the volume of the liquid to about 100
litres. At this moment the labours of the ' mother '
begin. Henceforward ten litres of vinegar may be drawn
off every eight days, to be replaced by ten litres of
wine. This is the maximum that a cask can yield in
a week. When the casks work badly, as is often the
case, it is necessary to diminish their production.

This Orleans system has many drawbacks. It
requires three or four months to prepare what is
called a ' mother,' which must be nourished with wine
very regularly once a week under penalty of seeing it
lose all its power. Then it is necessary to continue
the manufacture at all times, whether the vinegar
be required or not. To reconstitute a ' mother,' one
must begin from the very beginning, a process which
involves a loss of three or four months' time. Lastly
— a condition which is at times very inconvenient

78 LOUIS PASTEUE.

— a * mother ' cannot be transported from one place to
another, or even from one part of the same locality to
another. The 'mother,' in fact, must rest immovable.

Pasteur advised the suppression of the ' mothers.'
He recommended an apparatus, which is simply
a vat, placed in a chamber the temperature of which
can be raised to 20° or 25° Centigrade. In these
vats vinegar already formed is mixed with wine. On
the surface is sown the little plant which converts
the wine into vinegar. The mode of sowing it has
been already explained. The acetification begins with
the development of the plant.

A great merchant of Orleans, who had from the
first adopted Pasteur's process, and who had won the
prize offered by the * Society for the Encouragement
of National Industry' for a manufactory perfected
after these principles, has stated that at the end
of nine or ten days, sometimes even in eight, all
the acetified wine is converted into vinegar. From a
hundred litres of wine he drew off ninety-five litres of
vinegar. After the great rise of temperature observed
at the moment of the formation of the vinegar, and
which is caused by the chemical union of the alcohol
and the oxygen of the air, the vinegar is allowed to
cool. It may then be drawn from the vat, introduced
into barrels, refined, and straightway delivered, fit for
consumption. When the vat is quite emptied, and well
cleaned, a new mixture is made of vinegar and wine,

ACETIC FEKMENTATION. 79

the little plant is sown as before, and the same facts
are reproduced in the second as in the first operation.

In the vessels where vinegar is preserved, whether
in the manufactories, in private houses, or in grocers'
shops, it often happens that the liquid becomes turbid,
and impoverished in an extraordinary manner ; it even
ends in putrefaction, if a remedy be not promptly
applied. Pasteur has pointed out the cause of these
phenomena. After the alcohol has become acetic acid
by the combustive action of the mycoderm, the ques-
tion remains, what becomes of the mycoderm ? Most
frequently it falls to the bottom of the vessel, having
no more work to accomplish. This is a phase of the
manufacture which must be watched with care. It
is shown by the experiments of Pasteur that the
mycoderma aceti can live on vinegar already formed,
maintaining its power of fixing the oxygen on certain
constituents of the liquid. In this case the acetic
acid itself is the seat of the chemical action— in other
words, the oxygen unites with the carbon of the
acetic acid, and transforms it into carbonic acid, and
as the acetic acid has a composition which can be
represented by carbon and water, it follows that if
the combustion is allowed to take its course, instead
of vinegar we have eventually nothing but water
mixed with a small proportion of nitrogenous and
mineral matters, and the remains of the mycoderm.

80 LOUIS PASTEUR.

We have thus an ordinary organic infusion exempt
from all acidity, and one which could not be better
fitted to become the prey of the vibrios of putrefaction
or of the aerobic mucors. By these mucors, more-
over, which form a film on the surface of the liquid
after the mycoderm has fallen, the anaerobic vibrios
protected from the action of the air, can come into
active existence. Here we find ourselves in presence
of one of those double phenomena, of putrefaction in
the deeper parts of the liquid, and of combustion at
the surface which is in contact with the air. Nothing
is more prejudicial to the quality of the vinegar than
the setting in of this combustion after the vinegar has
been formed, and when it contains no more alcohol.
The first materials of the vinegar upon which the
oxygen transmitted by the mycoderm fixes are, in fact,
the ethereal and aromatic constituents which give to
vinegar its chief value.

Another cause of the deterioration of the quality
of vinegar, which is sometimes very annoying to the
manufacturer, consists in the frequent presence of
little eel-like organisms, very curious when viewed
with a strong magnifier. Their bodies are so trans-
parent that their internal organs can be easily dis-
tinguished. These eel-like creatures multiply with ex-
traordinary rapidity. Certainly there is not a single
barrel of vinegar manufactured by the Orleans system
which does not contain them in alarming numbers.

ACETIC FERMENTATION. 81

Prior to Pasteur's investigations, the ignorance re-
garding these organisms was such that they were
actually considered necessary to the production of the
vinegar ; whereas they are, on the contrary, most inimi-
cal to it, and must, if possible, be got rid of. This is,
moreover, rendered desirable by the repugnance which
is naturally felt to using a liquid denied by the presence
of such animalcules — a repugnance which becomes
almost insurmountable to anyone who has once seen
through a microscope the swarms contained in a drop
of vinegar. The mischief wrought by these little
beings in the manufacture of vinegar results from the
fact that they require air to live. The effect can
easily be perceived by filling to the brim a bottle of
vinegar, corking it, and then comparing it with a
similar bottle half filled with the same vinegar, and left
uncorked in contact with the air. In the first bottle,
the motions of the eel-like creatures become gradually
slower, until after a few days they cease to multiply
and fall lifeless to the bottom of the vessel. In the
second bottle, on the contrary, they continue to swarm
and move about. This need of oxygen is further de-
monstrated by the fact that, if the vinegar reaches a
certain depth in the bottle, life is suspended in the
lower parts, and the little eel-like organisms, in order
to breathe more freely, form a crawling zone in the
upper layers of the liquid.

Connecting these observations with the other fact

82 LOUIS PASTEUE.

that the vinegar is formed by the action of the myco-
dermic film on its surface, we can understand at once
that the mycoderm and the little eels continually
carry on a struggle for existence, since both of these
living things — the one animal the other vegetable —
imperiously demand the same aliment, oxygen. They
live, moreover, in the same superficial layers, a circum-
stance which gives rise to very curious phenomena.
When, for one reason or another, the film of myco-
derm is not formed, or when there is any delay in
its production, the little eels invade in such great
numbers the upper layers of the liquid that they
absorb all the oxygen. The little plant has in conse-
quence great difficulty in developing itself or even in
beginning its life. Eeciprocally, when the work of
acetification is active, and when the mycoderm has
occupied the upper layers, it gradually drives away
the eels, which take refuge, not deep down, where
they would perish, but against the moist sides of the
barrel or the vat. There they form a thick whitish
scum all in motion. It is a very curious spectacle.
Here their enemy, the mycoderm, can no longer
injure them to the same extent, since they are sur-
rounded with air ; and here they wait with impatience
for the moment when they can again take their place
in the liquid, and, in their turn, fight against the
mycoderm. In Pasteur's process, where the vats are
very often cleansed, it is easy to keep them free from

ACETIC FEKMENTATION. 83

these little animalcules ; they have not time to multiply
to a hurtful extent. Indeed, if the operation be well
conducted, they do not make their appearance at all.

Nearly all Pasteur's publications have had from
the moment of their appearance to undergo the severest
criticism. Their novelty caused them to clash with
the prejudices and errors current in science. His re-
searches on fermentation provoked lively opposition.
Liebig did not accept without recrimination a series
of researches which concurred in upsetting the theory
he had enunciated and defended in all his works.
After having kept silence for ten years, he published,
at Munich, where he was professor, a long memoir
entirely directed against Pasteur's results. In 1870,
on the eve of the war, Pasteur, who was at that time
returning from a scientific journey into Austria, deter-
mined to pass by Munich, with the view of attempting
to convince his distinguished adversary. Liebig re-
ceived him with great courtesy, but, hardly recovered
from an illness, he alleged his convalescence as a
reason for declining all discussion.

Then followed the Franco-German war. Hardly
was it terminated when Pasteur brought before the
Academy of Sciences a.t Paris a defence of what he
had published, as a sort of challenge to his illustrious
opponent. The memoir of Liebig was filled with the

most skilful arguments.

o 2

84 LOUIS PASTEUE.

' I pondered it for nearly ten years before producing
it,' he wrote. Pasteur, putting aside all subtleties of
argument, went straight to the two objections of the
German chemist which lay at the root of the discussion.

It may be remembered that one of the most de-
cisive proofs by which Pasteur overthrew Liebig's
theory resulted from the experiments in which by
the aid of mineral bodies and fermentable matter he
produced a special living ferment for each definite fer-
mentation. By removing all nitrogenous organic
matter, which in Liebig's theory constitutes the fer-
ment, Pasteur established, at one and the same time,
the life of the ferment and the absence of all action of
albuminoid matter in process of alteration. Liebig
here formally contested the fact that Pasteur had been
able to produce yeast and alcoholic fermentation in a
sweetened mineral medium by sowing therein an in-
finitesimal quantity of yeast. It is certain that, ten
years previously, when Pasteur announced the pro-
duction of yeast life and alcoholic fermentation under
such conditions, his experiment was one so difficult to
perform that it sometimes happened to Pasteur him-
self to be unable to reproduce it. The cells of yeast
sown in the sweetened mineral medium found them-
selves often associated with other microscopic or-
ganisms, which were singularly hurtful to the life of
the yeast. Pasteur was at this period far from being
familiarised with the delicacy which such experiments

ACETIC FEEMENTATION. 85

require, and he did not yet know all the precau-
tions indicated later on, which were indispensable to
success. Though in his original memoir of 1860
Pasteur had pointed out the difficulties of his experi-
ment, these difficulties existed nevertheless. Liebig
took hold of them with skill, exaggerated them ; saw,
so to speak, nothing but them ; and declared that the
results announced never could have been obtained.
But in 1871 the fundamental experiment of Pasteur,
on the life of yeast in a sweetened mineral medium,
had become a trifle for him. He knew exactly how
to form media deprived of all foreign germs, how to
prepare pure yeast, and how to prevent the introduc-
tion of new germs, which could develop in the liquids
and hinder the life of the yeast.

* Choose,' said he to Liebig, ' from the members
of the Academy one or several, and ask them to de-
cide between you and me. I am ready to prepare
before you and before them, in a sweetened mineral
medium, as much yeast as you can reasonably ask for,
and with substances provided by yourself.'

Liebig's second objection had reference to acetic
fermentation. The process of acetification known as
that of * beech shavings ' is widely practised in Germany
and even in France. It consists in causing alcohol
diluted with water and with the addition of some
millicmes of acetic acid to trickle slowly into barrels
or vats filled with shavings of beech, either massed

86 , LOUIS PASTEUE.

together without order or disposed in layers after hav-
ing been rolled up like the spring of a watch. Openings
formed in the sides of the barrel, and in a double
bottom upon which the shavings rest, permit the
access of the air, which rises into the barrel as it
would in a chimney, and yields all or part of its
oxygen to the alcohol to convert it into acetic acid.
All writers prior to Pasteur, and Liebig in particular,
maintained that the shavings acted like porous bodies
in the same manner as finely divided platinum. The
acetic acid, they said, was formed by a direct oxidation,
without any other influence than the porosity of the
wood. This view of the subject was rendered plausible
by the fact that in many manufactories the alcohol
employed is that of distillation, which contains no al-
buminoid substances. Moreover, the duration of the
shavings is in a sense indefinite.

According to Pasteur, the shavings perform only a
passive part in the manufacture. They promote the
division of the liquid and cause a considerable aug-
mentation of the surface exposed to the air. They
moreover serve as a support for the ferment, which is
still, according to him, the mycoderma aceti, under the
mucous form proper to it when submerged.

Certainly appearances were far from being favour-
able to this view. When the shavings of a barrel
which has been in work for several months or even for
several years are examined, they are found to be extra-

ACETIC FEKMENTATION. 87

ordinarily clean. It might be said that they had just
been carefully washed. Pasteur has shown that this
is but a deceptive appearance, and that in reality
these shavings are partly or wholly covered with a
mucous film of mycoderma aceti of excessive tenuity.
It is necessary to scrape the surface of the wood with a
scalpel and examine the scrapings with the microscope
to be assured of the presence of this pellicle.

Liebig, who somewhere speaks, not without a cer-
tain contempt, of the microscope, denied formally the
exactitude of these assertions.

* With diluted alcohol, which is used for the rapid
manufacture of vinegar,' he wrote, * the elements of
nutrition of the mycoderm are excluded, and the
vinegar is made without its intervention.' He asserted
also in his memoir of 1869 that he had consulted the
head of one of the principal manufactories of vinegar
in Germany, that in this manufactory the diluted al-
cohol did not receive during the whole course of its trans-
formation any foreign addition, and that beyond the air
and the surfaces of wood and charcoal — for charcoal is
sometimes associated with the beech shavings — nothing
can act upon the alcohol. Liebig added that the
director of the manufactory did not believe at all in
the presence of the mycoderm, and that finally he,
Liebig, in examining the shavings which had been
used for twenty-five years in the manufactory, saw no
trace of mycoderm on their surface.

88 LOUIS PASTEUE.

The argument appeared conclusive. How, in fact,
could we understand the production of a plant con-
taining within itself nitrogen and mineral elements
which was nevertheless to be nourished by water and
alcohol.

* You do not take into account,' replied Pasteur,
' the nature of the water which serves to dilute your
alcohol. This water, like all ordinary waters, even
the purest, contains salts of ammonia and mineral
matters which are capable of nourishing the plant.
Finally, you have not rightly examined with the micro-
scope the surface of the shavings, otherwise you would
have seen the little particles of the mycoderma aceti
united, in some cases, to a thin film which can even be
lifted up. I propose to you, moreover, to send to the
Academic Commission charged with the decision of the
debate, some shavings that you have obtained yourself
in the manufactory at Munich, and in the presence of
its director. I will undertake to prove before the mem-
bers of the commission the presence of the mycoderm
on the surface of these shavings.'

Liebig did not accept this challenge. To-day the
question is decided.

89

THE QUESTION OF SPONTANEOUS
GENERATION.

* ALL dry bodies,' said Aristotle, ' which become damp,
and all damp bodies which are dried, engender animal
life.' Bees, according to Virgil, are produced from
the corrupted entrails of a young bull. At the time
of Louis XIV. we were hardly more advanced. A
celebrated alchemist doctor, Van Helmont, wrote :
' The smells which rise from the bottom of morasses
produce frogs, slugs, leeches, grasses, and other
things.' But most extraordinary of all was the true
recipe given by Van Helmont for producing a pot
of mice. It suffices to press a dirty shirt into the
orifice of a vessel containing a little corn. After about
twenty-one days, the ferment proceeding from the dirty
shirt modified by the odour of the corn effects the trans-
mutation of the wheat into mice. Van Helmont, who
asserted that he had witnessed the fact, added with
assurance :

' The mice are born full grown ; there are both

90 LOUIS PASTEUE.

males and females. To reproduce the species it
suffices to pair them.'

* Scoop out a hole,' said he again, ' in a brick, put
into it some sweet basil, crushed, lay a second brick
upon the first so that the hole may be perfectly
covered. Expose the two bricks to the sun, and at
the end of a few days the smell of the sweet basil,
acting as a ferment, will change the herb into real
scorpions. An Italian naturalist, Kedi, was the first
to subject this question of spontaneous generation
to a more attentive examination. He showed that
maggots in meat are not spontaneously generated,
but that they are the larvae of flies' eggs. To prevent
the production of maggots, Kedi showed that it was
only necessary to surround the meat with fine gauze
before exposing it to the air. As no flies could alight
upon meat thus protected, there were no eggs de-
posited, and consequently neither larvae nor maggots.
But at the moment when the doctrine of spontaneous
generation began to lose ground by the limitation of
its domain, the discovery of the microscope brought
to this doctrine new and formidable support. In pre-
sence of the world of animalculse, the partisans of
spontaneous generation raised a note of triumph.
' We may have been mistaken,' they said, ' as to the
origin of 'mice and maggots, but is it possible to
believe that microscopic organisms are not the out-
come of spontaneous generation ? How can we other-

THE QUESTION OF SPONTANEOUS GENERATION. 91

wise explain their presence and rapid multiplication
in all dead animal or vegetable matter in process of
decomposition ? '

Buffon lent the authority of his name to the doc-
trine of spontaneous generation. He even devised
a system to explain this hypothesis. In 1745 two
ecclesiastics entered upon an eager controversy for
and against this question. While the English Catholic
priest Needham adopted the theory of spontaneous
generation, the Italian priest Spallanzani energetically
opposed it ; but while in the eyes of the public the
Italian remained master of the dispute, his success was
more apparent than real, more in word than in deed.

The problem was again brought forward in a more
emphatic manner in 1858. M. Pouchet, director of
the Museum of Natural History at Eouen, in address-
ing the Academy of Sciences, declared that he had
succeeded in demonstrating in a manner absolutely
certain the existence of microscopic living organisms,
which had come into the world without germs, and
consequently without parents similar to themselves.

How came Pasteur to throw himself into this dis-
cussion, at first sight so far removed from his other
occupations? The results of his researches on fer-
mentation led him to it as a sort of duty. He was
carried on by a series of logical deductions. Let us
recall to mind, for example, the experiment in which
Pasteur exposed to the heat of the sun water sweetened

92 LOUIS PASTEUR.

with sugar and mixed with phosphates of potash and
magnesia, a little sulphate of ammonia, and some car-
bonate of lime. In these conditions the lactic fermen-
tation was often seen to develop itself — that is to say,
the sugar became lactic acid, which combined with the
lime of the carbonate to form lactate of lime. This
salt crystallises in long needles, and ends sometimes by
filling the whole vase, while a little organised living
thing is at the same time produced and multiplied. If
the experiment is carried on further, another fermenta-
tion generally succeeds to this one. Moving vibrios
make their appearance and multiply, the lactate of lime
disappears, the fluidity returns to the mass, and the
lactate finds itself replaced by butyrate of lime. What
a succession of strange phenomena ! How did life
appear in this sweetened medium, composed originally
of such simple elements, and apparently so far re-
moved from all production of life? This lactic fer-
ment, these butyric vibrios, whence do they come ?
Are they formed of themselves ? or are they produced
by germs ? If the latter, whence do the germs come ?
The appearance of living organised ferments had be-
come for Pasteur the all-important question, since in
all fermentations he had observed a correlation between
the chemical action set up and the presence of micro-
scopic organisms. Prior to the establishment of the
facts already mentioned, these difficulties did not exist.
The theory of Liebig was universally accepted.

THE QUESTION OF SPONTANEOUS GENERATION. 93

Thus the question as to the origin of microscopic
organisms and the part played by them in fermenta-
tion was imposed as a necessity on Pasteur. He
could not proceed further in his researches without
having solved this question.

In the month of October, 1857, Pasteur was called
to Paris. After having been made dean at an incredibly
early age, he was now, at the age of thirty-five, entrusted
with the scientific studies at the Ecole Normale
Superieure. But if the position was flattering, it did not
give to Pasteur what he most desired. As he had no
Professor's chair, he had no laboratory. In those days
science, and the higher education in science, were at a
discount. It was the period when Claude Bernard
lived in a small damp laboratory, when M. Berthelot,
though known through his great labours, was still
nothing more than an assistant in the College de
France.

At the time here referred to, the Minister of Public
Instruction said to Pasteur, ' There is no clause in
the budget to grant you 1,500 francs a year to defray
the expense of experiments.' Pasteur did not hesitate
to establish a laboratory at his own expense in one of
the garrets of the Ecole Normale. We can readily ima-
gine the modesty of such an establishment in such a
place. Dividing his time between his professional
duties and his laboratory experiments, Pasteur never
went out but to talk over his daily researches with

94 LOUIS PASTEUR.

M. Biot, M. Dumas, M. de Senarmont, and M. Balard.
M. Biot especially was his habitual confidant. The
day when M. Biot learned that Pasteur proposed to
study the obscure question of spontaneous generation,
he strongly dissuaded him from entangling himself in
this labyrinth. * You will never escape from it,' said
he, ' you will only lose your time ; ' and when Pasteur
attempted some timid observations with the view of
showing that in the order of his studies it was in-
dispensable for him to attack this problem, M. Biot
grew angry. Although endowed, as Sainte-Beuve has
said, with all the qualities of curiosity, of subtlety, of
penetration, of ingenious exactitude, of method, and
of perspicuity, with all the qualities, in short, essential
and secondary, M. Biot treated the project of Pasteur
as a presumptuous adventure.

Bolder than M. Biot, but with a circumspection
always alive, M. Dumas declared to Pasteur, without,
however, further insisting upon the point, that he
would not advise anyone to occupy himself too long
with such a subject. M. de Senarmont alone took
the part of Pasteur, and said to M. Biot :

' Let Pasteur alone. If there is nothing to be
found in the path which he has entered upon, do not
be alarmed, he will not continue in it. But,' added
he, ' I should be surprised if he found nothing in it.'

M. Pouchet had previously stated the problem
with precision :

THE QUESTION OF SPONTANEOUS GENERATION. 95

' The opponents of spontaneous generation assert
that the germs of microscopic organisms exist in the
air, which transports them to a distance. What, then,
will these opponents say if I succeed in inducing the
generation of living organisms, while substituting
artificial air for that of the atmosphere ? '

Pouchet then devised this ingenious experiment.
He filled a bottle with boiling water, hermetically sealed
it with the greatest care, and plunged it upside down
into a basin of mercury. When the water was quite
cold he uncorked the bottle under the metal, and in-
troduced into it half a litre of pure oxygen gas, which
is as necessary to the life of the smallest microscopic
organism as it is to that of the larger animals and
vegetables. Up to this time there was nothing in the
vessel but pure water and oxygen. Pouchet then in-
troduced a minute bunch of hay which had been
enclosed in a corked bottle, and exposed in a stove
for a long time to a temperature of more than 100
degrees. At the end of eight days a mouldiness
was developed in this infusion of hay. ' Where
does this come from ? ' cried M. Pouchet triumphantly.
Certainly not from the oxygen, which had been pre-
pared from a chemical compound at the temperature
of incandescence. The water had been equally deprived
of germs, since at the boiling temperature all germs
would have been destroyed. The hay also could not
have contained them, for it had been taken from a

96 LOUIS PASTEUR.

stove heated to 100 degrees. As it was urged, how-
ever, that certain organisms could resist this tempera-
ture, M. Pouchet heated the hay from 200 to 300
degrees, or to any temperature that might be
desired.

Pasteur came to disturb the triumph of M.
Pouchet.

In a lecture which he gave at the Sorbonne in
1864, before a large assembly composed of savants,
philosophers, ladies, priests, and novelists — Alexandre
Dumas was in the first row — all showing eager interest
in the problems to be dealt with in the lecture,
Pasteur thus criticised the experiment of Pouchet:
' This experiment is irreproachable, but irreproachable
only on those points which have attracted the atten-
tion of its author. I will demonstrate before you that
there is a cause of error which M. Pouchet has not
perceived, which he has not in the least suspected,
which no one before him suspected, but which
renders his experiment as completely illusory as
that of Van Helmont's pot of dirty linen. I will
show you where the mice got in. I will prove to
you, in short, that it is the mercury which carries the
germs into the vessels, or, rather, not to go beyond
the demonstrated fact, the dust which is suspended in
the air.'

To render visible this floating dust, Pasteur caused
the hall to be darkened, and pierced the obscurity by a

THE QUESTION OF SPONTANEOUS GENERATION. 97

beam of light. There then appeared, dancing and twirl-
ing in the beam, thousands of little particles of dust.

'If we had time to examine them well,' continued
Pasteur, 'we should see them, though agitated with
various movements, falling downwards more or less
quickly. It is thus that all objects become covered
with dust — the furniture, the table, the mercury in
this basin. Since this mercury was taken from the
mine, how much dust must have fallen upon it, to say
nothing of all that has been intimately mixed up
with it during the numerous manipulations to which
it has been subjected in the laboratory ? It is not
possible to touch this mercury, to place the hand in
it, or a bottle, without introducing into the interior of
the basin the dust which lies on its surface. You
will now see what takes place.'

Projecting, in the darkness, the beam of light upon
the basin of mercury, the liquid metal shone forth with
its usual brilliancy. Pasteur then sprinkled some dust
upon the mercury, and, plunging a glass rod into it,
the dust was seen to travel towards the spot where
the rod entered the mercury, and to penetrate into the
space between the glass and the metal.

' Yes,' exclaimed Pasteur with a voice which gave
evidence of the sincerity of his conviction, 'yes, M.
Pouchet had removed the germs from the water and
from the hay, but he had neglected to remove the
dust from the surface of the mercury. This is the

98 LOUIS PASTEUR.

cause of his error ; this is what has vitiated his whole
arrangement.'

Pasteur then instituted experiments exactly similar
to those of Pouchet, hut taking care to remove every
cause of error which had escaped the latter. He em-
ployed a glass bulh with a long neck, which he bent,
and connected with a tube of platinum placed in a
furnace, so that it could be heated nearly to redness.
In the bulb he placed some very putrescible liquids—
urine for example. When the furnace which sur-
rounded the platinum tube was in action, Pasteur
boiled the liquid for some minutes, then he allowed it
to cool, keeping the fire around the platinum tube
still active. During the cooling of the bulb the ex-
ternal air was introduced, after having first travelled
through the red-hot platinum tube. The liquid was
thus placed in contact with air whose suspended
germs were all burnt up.

In an experiment thus carried out, the urine
remains unchanged — it undergoes only a very slight
oxidation, which darkens its colour a little — but it
exhibits no kind of putrefaction. If it be desired to
repeat this experiment with alkaline liquids, such as
milk, the temperature must be raised a little above
the boiling point — a condition easily realised with the
apparatus just described. It is only necessary to
connect with the free extremity of the platinum tube
a glass tube bent at right angles, and to plunge the
latter to a depth of some centimeters into a basin of

THE QUESTION OF SPONTANEOUS GENEKATION. 99

mercury. In these circumstances ebullition goes on
under a pressure greater than that of the atmo-
sphere, consequently at a temperature higher than
100 degrees Centigrade.

It remained, however, to be proved that the floating
dust of the air embraces the germs of the lower
organisms. Through a tube stopped with cotton
wool, Pasteur, by means of an aspirator, drew ordi-
nary air. In passing through the wool it was filtered,
depositing therein all its dust. Taking a watch-glass,
Pasteur placed on it a drop of water in which he
steeped the cotton wool stopper and squeezed out of
it, upon a glass slide, a drop of water which contained
a portion of the intercepted dust. He repeated this
process until he had extracted from the cotton nearly
all the intercepted dust. The operation is simple and
easily executed. Placing the glass slide with a little of
the soiled liquid under a microscope, we can dis-
tinguish particles of soot, fragments of silk, scraps of
wool, or of cotton. But, in the midst of this inani-

I mate dust, living particles make their appearance —
that is to say, organisms belonging to the animal or

I vegetable kingdom, eggs of infusoria, and spores of
cryptogams. Germs, animalculae, flakes of mildew,
float in the atmosphere, ready to fall into any appro-

, priate medium, and to develop themselves at a pro-

! digious rate*

But are these apparently organised particles

100 LOUIS PASTEUR

which are found thus associated with amorphous dust
indeed the germs of microscopic living beings ? Grant-
ing the experiment devised by Pasteur to verify that
of Pouchet to be irreproachable, is Pasteur's interpre-
tation of it rigorously true ? In presence of the
problem of the origin of life, all hypotheses are pos-
sible as long as the truth has not been clearly
revealed. Truly, it might be argued, if fermenta-
tion be caused by germs, then the air which has
passed through a red-hot platinum tube cannot pro-
voke fermentation, or putrefaction, or the formation
of organisms, because the germs of these last, which
were suspended in the air, have lost all vitality. But
what right have you to speak of germs ? How do
you know that the previous existence of germs is
necessary to the appearance and development of
microscopic organisms ? May not the prime mover
of the life of microscopic organisms be some appro-
priate medium started into activity by magnetism,
electricity, or even ozone ? Now, by the passing of the
air through your red-hot platinum tube these active
powers are destroyed, and the sterility of your bulb of
urine has nothing surprising in it.

The partisans of spontaneous generation had
often employed this apparently formidable reasoning,
and Pasteur thought it necessary to strengthen the
proof that the cotton wool through which his air had
filtered was really charged with germs.

THE QUESTION OF SPONTANEOUS GENERATION. 101

By an ingenious method he sowed the contents of
the cotton wool in the same liquids that had been
rendered sterile by boiling. The liquids became fertile,
even more fertile than if they had been exposed to the
free contact of atmospheric air. Now, what was there
in the dust contained in the cotton wool? Only
amorphous particles of silk, cotton, starch; and,
along with these, minute bodies which, by their trans-
parency and their structure, were not to be distin-
guished from the germs of microscopic organisms.
The presence of imponderable fluids could not here be
pleaded.

Nevertheless, fearing that determined scepticism
might still attribute to the cotton wool an influence of
some sort on account of its being an organised sub-
stance, Pasteur substituted for the stoppers of cotton
wool stoppers of asbestos previously heated to red-
ness. The result was the same.

Wishing still further to dispose of the hypothesis
that, in ordinary air, an unknown something existed
which, independent of germs, might be the cause
of the observed microscopic life, Pasteur began a new
series of experiments as simple as they were demon-
strative. Having placed a very putrescible infusion —
in other words, one very appropriate to the appearance
of microscopic organisms — in a glass bulb with a long
neck, by means of the blowpipe, he drew out this neck

102 LOUIS PASTEUR.

to a very small diameter, at the same time bending
the soft glass to and fro, so as to form a sinuous tube.
The extremity of this narrow tube remained open.
He then boiled his liquid for some minutes until the
vapour of the water came out in abundance through
the narrow open tube. In these conditions the liquid
in the bulb, however putrescible, is preserved indefi-
nitely without the least alteration. One may handle
it, transport it from place to place, expose it to every
variety of climate, place it in a stove with a tempera-
ture of thirty or forty degrees, the liquid remains as
clear as it was at first. A slight oxidation of the
constituents of the liquid, is barely perceptible. In
this experiment the ordinary air, entering suddenly
at the first moment, finds in the bulb a liquid very
near the boiling temperature; and when the liquid
is so far cooled that it can no longer destroy the
vitality of the germs, the entrance of the air is cor-
respondingly retarded, so that the germs capable of
acting upon the liquid, and of producing in it living
organisms, are deposited in the bends of the still
moist tube, not coming into contact with the liquid
at all.

If, after remaining for weeks, months, or even
years, in a heated chamber, the sinuous neck of the
bulb is snipped off by a file in the vertical part of the
stem, after twenty-four or forty-eight hours there
begin to appear mildew, mucors, bacteria, infusoria,

THE QUESTION OF SPONTANEOUS GENERATION. ' 103

exactly as in the case of infusions recently exposed to
the contact of ordinary air,

The same experiments may be repeated with
slightly alkaline liquids, such as milk, the precaution
being taken of raising them to a temperature higher
than that of 100 degrees Centigrade.

The great interest of Pasteur's method consists in
its proving unanswerably that the origin of life, in
infusions which have been heated to the boiling point,
is solely due to the solid particles suspended in the
air. Of gas, electricity, magnetism, ozone, things
known or unknown, there is nothing in ordinary
atmospheric air which, apart from these solid par-
ticles, can cause the fermentation or putrefaction of
the infusions.

Lastly, to convince the most prejudiced minds,
and to leave no contradiction standing, Pasteur
showed one of these bulbs with the sinuous neck which
he had prepared and preserved for months and years.
The bulb was covered with dust. ' Let us,' said he,
1 take up a little of this outside dust on a bit of glass,
porcelain, or platinum, and introduce it into the
liquid; the following day you will find that the in-
fusion, which up to this time remained perfectly clear,
has become turbid, and that it behaves in the same
manner as other infusions in contact with ordinary
air.'

If the bulb be tilted so as to cause a little drop

104 LOUIS PASTEUK.

of the clear infusion to reach the extremity of the
bent part of the neck where the dust particles are
arrested, and if this drop be then allowed to trickle
back into the infusion, the result is the same — tur-
bidity supervenes and the microscopic organisms are
developed. Finally, if one of those bulbs which have
stood the test of months and years without alteration
be several times shaken violently, so that the external
air shall rush into it, and if it be then placed once
more in the stove, life will soon appear in it.

In 1860 the Academy of Sciences had offered a
prize, the conditions of which were stated in the
following terms :

* To endeavour by well-contrived experiments to
throw new light upon the question of spontaneous
generation.' The Academy added that it demanded
precise and rigorous experiments equally well studied
on all sides; such experiments, in short, as should
render it possible to deduce from them results free
from all confusion due to the experiments themselves.
Pasteur carried away the prize, and no one, it will be
acknowledged, deserved it better than he. Neverthe-
less, to his eyes, the subject was still beset with diffi-
culties. In the hot discussions to which the question
of spontaneous generation gave rise, the partisans of
the doctrine continually brought forward an objection
based on an opinion already referred to, and first
enunciated by Gay-Lussac. As already known to the

THE QUESTION OF SPONTANEOUS GENERATION. 105

reader, Gay-Lussac had arrived at the conclusion that,
in Appert's process, one condition of the preservation
of animal and vegetable substances consisted in the
exclusion of oxygen.

Even this proposition was soon improved upon,
and it became a current opinion in science that the
smallest bubble of oxygen or of air which might come
in contact with a preserve would be sufficient to start its
decomposition. The partisans of spontaneous genera-
tion— the heterogenists — thenceforward threw their
objections to Pasteur into this form :

' How can the germs of microscopic organisms be
so numerous that even the smallest bubble of air
contains germs capable of developing themselves in
every organic infusion ? If such were the case the
air would be encumbered with organic germs.' M.
Pouchet said and wrote that they would form a thick
fog, as dense as iron.

But Pasteur showed that the interpretation of
Gay-Lussac' s experiment, with respect to the possible
alteration of preserves by a small quantity of oxygen
gas, was quite erroneous. If, after a certain time, an
Appert preserve contains no oxygen, this is simply
because the oxygen has been gradually absorbed by
the substances of the preserve, which are always more
or less chemically oxidisable. But in reality it is easy
to find oxygen in these preserves. Pasteur did not
fail to perceive that the interpretation given to Gay-

106 LOUIS PASTEUE.

Lussac's experiment was wrong in another particular.
He proved the fallacy of the assumption that the
smallest quantity of air was always capable of pro-
ducing microscopic organisms.

More thickly spread in towns than in the country,
the germs become fewer in proportion as they recede
from human habitations. Mountains have fewer
than plains, and at a certain height they are very
rare.

Pasteur's experiments to prove these facts were
extremely simple. He took a series of bulbs of about
a quarter of a litre in capacity, and, after having half
filled the bulbs with a putrescible liquid, he drew out
the necks by means of the blowpipe, then he caused
the liquid to boil for some minutes, and during the
ebullition, while the steam issued from the tapering
ends of the bulbs, he sealed them .with the lamp. Thus
prepared, the bulbs can be easily transported. As
they are empty of air — that which they originally
contained having been driven out with the steam-
when the sealed end of a bulb is broken off, the air
rushes into the tube, carrying with it all the germs
which this air holds in suspension. If it is closed
again immediately afterwards by a flame, and if the
vessels are then left to themselves, it is easy to
recognise those in which a change occurs. Now,
Pasteur established that, in whatever place the opera-
tion might be carried on, a certain number of bulbs

THE QUESTION OF SPONTANEOUS GENERATION. 107

would escape alteration. They must not, however, he
opened in a room after dusting the furniture or sweep-
ing the floor, for in this case all the bulbs would become
altered because of the great quantity of germs raised
by the dusting and remaining suspended in the air.

Pasteur started for Arbois with a series of bulbs.
Some he opened in the country far from all habitations ;
others he opened at the foot of the mountains which
form the first range of the Jura ; a series of twenty-
four bulbs was opened upon Mount Poupet, at 850
meters above the level of the sea ; and, lastly, twenty
others were transported to the Montanvert, near the
Mer de Glace, at an elevation of 2,000 meters. He
afterwards brought his whole collection back to Paris,
and in the month of November, 1860, deposited them
on the table at the Academy of Sciences.

Of the twenty bulbs first opened in the country,
eight contained organised productions. Of the twenty
opened on the heights of the Jura, five only were
altered, and of the twenty opened upon the Montan-
vert during a strong wind which blew from the
glacier, one alone was altered.

If a similar series of experiments were made in a
balloon, it would be found that the air of the higher
atmosphere is absolutely free from germs. Care
would, however, be necessary to prevent the introduc-
tion of dust particles, which the rigging and the
aeronauts themselves might carry with them.

108 LOUIS PASTEUR.

But we have not yet related all. So far, all these
conclusive experiments had been made only on organic
liquids, very putrescible it is true, but which had all
been subjected to boiling or even to temperatures
higher than 100 degrees Centigrade. The partisans
of spontaneous generation might then be justified in
saying that if the precaution had been taken of putting
into contact with pure air natural organic liquids in a
state compatible with the operations of animal and vege-
table life, the results would have been different. Under
such conditions, life would have appeared spontaneously
in the production of microscopic organisms. None of
Pasteur's opponents had formulated this argument;
but Pasteur himself, who had within him an adversary
always present, always on the alert, prepared to yield
only to accumulated proofs, saw this objection.
He was not satisfied until he had succeeded in com-
pletely refuting it. Having by means of ingenious
experimental arrangements deprived some air of all
living germs, he placed in contact with this pure
air the most putrescible liquids, particularly venous
blood, arterial blood, and urine. He took these
liquids directly from the veins, the arteries, and the
bladders of animals in full health. No alteration
was produced. In due time a chemical absorption of
small quantities of oxygen took place, but neither
fermentation nor putrefaction, nor the smallest deve-
lopment of bacteria, of vibrios, or of mould. After

THE QUESTION OF SPONTANEOUS GENERATION. 109

this, Pasteur was able legitimately to exclaim in his
celebrated lecture at the Sorbonne :

' There is not one circumstance known at the
present day which justifies the assertion that micro-
scopic organisms come into the world without germs
or without parents like themselves. Those who main-
tain the contrary have been the dupes of illusions and
of ill-conducted experiments, tainted with errors which
they know not how either to perceive or to avoid.
Spontaneous generation is a chimera.'

Pasteur was not alone in affirming this fixed con-
viction. With the authority of a judge delivering
sentence in court, M. Flourens, permanent Secretary
of the Academy of Sciences, pronounced these words
before the whole Academy :

'As long as my opinion was not formed I had
nothing to say; now it is formed and I can speak.
The experiments are decisive. If spontaneous genera-
tion be a fact, what is necessary for the production of
animalcule? Air and putrescible liquids. Now
Pasteur puts together air and putrescible liquids and
nothing is produced. Spontaneous generation, then,
has no existence. Those who still doubt have failed
to grasp the question.'

But some adversaries remained incredulous. When
Pasteur had announced the result of his experiments,
and brought before the Academy his series of bulbs,
Pouchet and Joly declared that if Pasteur had opened

110 LOUIS PASTEUE.

his bulbs in the Jura and on the Mer de Glace, they,
on their part, had been on the top of the Maladetta,
and had proved there the inexactitude of Pasteur's
results.

Pasteur asked to be judged by the Academy.
'A commission alone,' said he, 'will terminate the
debate.' The commission was named, and the position
on both sides was clearly stated.

' I affirm,' said Pasteur, ' that everywhere it is
possible to take from the midst of the atmosphere a
certain quantity of air which contains neither egg
nor spore, and which does not produce organisms in
putrescible solutions.'

On his side, M. Joly wrote : ' If one alone of your
bulbs remains unaltered we shall loyally acknowledge
our defeat.' Lastly, M. Pouch et, as distinct and
positive as M. Pasteur, said : * I affirm that in what-
ever place I take a cubic decimeter of air, when this
air is placed in contact with a fermentable liquid en-
closed in a glass vessel hermetically sealed, the liquid
will become filled with living organisms.'

This double declaration, which excited at that time
all the learned world, took place in the month of
January, 1864. Eager to engage in the combat,
Pasteur waited impatiently for the order of the Com-
mission that this experiment, which was to decide
everything, should be made. But M. Pouchet begged
for a postponement, desiring, he said, to wait for the

THE QUESTION OF SPONTANEOUS GENEEATION. Ill

warm season. Pasteur was astonished, but resigned
himself to the delay. The Commission and the
opponents met on June 15.

The Commission announced, ' that, as the whole
dispute turned upon one simple fact, one single
experiment ought to be undertaken, which alone
would close the discussion.'

The partisans of spontaneous generation wished
nevertheless to go through the entire series of their
experiments. In vain the Commission tried to per-
suade them that this would make the judgment as
long as the discussion itself had been, that all bore
upon one fact, and that this fact could be decided by
a single experiment. The heterogenists would not
listen to this. M. Pouchet and M. Joly withdrew
from the contest.

M. Jamin, an exact and authorised historian of
these debates, observed that ' the heterogenists, how-
ever they may have covered their retreat, were there-
by self -condemned. If they had been sure of the
fact — which they were solemnly engaged to prove,
under penalty of acknowledging themselves defeated —
they would have hastened to demonstrate it, for it
would have been the triumph of their doctrine. People
do not allow themselves to be condemned by default
except in causes in which they have no confidence.'

112 LOUIS PASTEUK.

STUDIES ON WINE.

HAVING thus solved the problem of spontaneous
generation, a problem which was but a parenthesis
forced upon his attention, Pasteur returned to fer-
mentation. Guided by his studies on vinegar and
other observations of detail, he undertook an inquiry
into the diseases of wine. The explanations of the
changes which wine was known to undergo rested
only on hypothesis. From the time of Chaptal, who
was followed by Liebig and Berzelius, all the world
believed wine to be a liquid in which the various
constituents react upon each other mutually and
slowly. The wine was thought to be continually
' working.' When the fermentation of the grape is
finished, equilibrium is not quite established between
the diverse elements of the liquor. Time is needed
for them to blend together. If this reciprocal action
be not regular, the wine becomes bad. This was, in
other words, the doctrine of spontaneity. Without
support from carefully reasoned experiments, these
explanations could not satisfy Pasteur, especially at a

STUDIES ON WINE. 113

moment when he had just been proving that there
was nothing spontaneous either in the phenomena of
fermentation or in animal and vegetable infusions.

Pasteur tried first of all to show that wine does
not ' work ' as much as it was supposed to do. Wine
being a mixture of different substances, among which
are acids and alcohol, particular ethers are no doubt
formed in it in course of time, and similar reactions
perhaps take place between the other constituents of
the liquid. But if the exactitude of such facts cannot
be denied, based as they are upon general laws, con-
firmed and extended by recent inquiries, Pasteur
thought that a false application was made of them
when they were employed to explain the maladies of
wine, the changes which occur in it through age — in
a word, the alterations, whether good or bad, which
wines are subject to. The 'ageing' of wine soon
appeared to him to consist essentially in the phe-
nomena of oxidation, due to the oxygen of the air
which dissolves and is diffused in the wine. He
gave manifest proofs of this. I will only mention
one of them. New wine inclosed in a glass vessel
hermetically sealed keeps its freshness ; it does not
* work,' it does not ' age.' Pasteur demonstrated
besides, that all the processes of wine-making are
explained by the double necessity of oxygenising the
wine to a suitable degree, and of preventing its dete-
rioration. In seeking for the actual causes of in-

i

114 LOUIS PASTEUR.

jurious alterations, Pasteur, always obedient to a pre-
conceived idea, while carefully controlling it with the
utmost rigour of the experimental method, asked him-
self whether the diseases of wine did not proceed from
organised ferments, from little microscopic vegeta-
tions ? In the observed alterations, he thought, there
must be some influences at work foreign to the normal
composition of the wine.

This hypothesis was verified. In his hands the in-
jurious modifications suffered by wines were shown to
be correlative with the presence and the multiplication
of microscopic vegetations. Such growths alter the
wine, either by subtracting from it what they need for
their nourishment, or, and principally, by forming new
products which are the effect of the multiplication of
these parasites in the mass of the wine.

Everyone knows what is meant by acid nine,
sharp ii'ine, sour ivine. The former experiments of
Pasteur had clearly shown that no wine can become
acid, sharp — can, in a word, become vinegar — without
the presence of a little microscopic fungus known by
the name of mycoderma aceti. This little plant is the
necessary agent in the condensation of the oxygen of
the air, and its fixation on the alcohol of the wine.
Chaptal, who published a volume on the art of wine-
making, knew of the existence of these mycoderm
flowers ; but to his eyes they were only ' elementary
forms of vegetation,' which had no influence whatever

STUDIES ON WINE. 115

upon the quality of the liquid. Besides the myco-
derma aceti, which is the agent of acetification, there
is another mycoderm called mycoderma vini. This
one deposits nothing which is hurtful to the wine,
and its flowers are developed by preference in new
wines, still immature, and preserving the astringency
of the first period of their fabrication.

The requirements of the two sorts of flowers are
such that even when the flower of vinegar is sown on
the surface of a new wine, no development takes
place. Conversely, the mycoderma vini sown on wines
that have grown old in casks or in bottles will
refuse to multiply. The mycoderma vini produces
no alteration in the wine ; it does not turn the wine
acid. In proportion as the wine grows old the flower
tends to disappear, the wine ' despoils ' itself, to
use a technical expression ; physiologically speaking,
the wine loses its aptitude to nourish the mycoderma
vini, which, finding itself progressively deprived of
appropriate nourishment, fades and withers. But it
is then that the mycoderma aceti appears, and multi-
plies with a facility so much the greater that it draws
its first nourishment from the cells of the mycoderma
vini. The mycoderma aceti has played so large a part
in the early pages of this book that it is not necessary
to go back upon it here.

There is another disease very common among
wines when the great heat of summer begins to make

i 2

116 LOUIS PASTEUR.

itself felt in the vintage tubs. The wine is said to
turn, to rise, to spurt. The wine becomes slightly
turbid and at the same time flat and piquant.
When it is poured into a glass, very small bubbles
of gas form like a crown upon the surface. On
placing the glass between the eye and the light
and slightly shaking it, one can distinguish silky
waves shifting about and moving in different direc-
tions in the liquid. When the turned wine is in a
cask, it is not unusual to see the bottom of the cask
bulge a little, and sometimes a leakage takes place at
the joints of the staves. If 'a little opening is made,
the wine spurts out, and that is the reason why the
wine is said to spurt.

Authors who have written on the subject of
wine attributed this malady to the rising of the lees.
They believed that the deposit which always exists in
greater or less quantities in the lower part of the
cask rises and spreads itself into all the mass of the
wine.

Nothing can be more inexact. If this phenomenon
is sometimes produced — that is to say, if the deposit
rises into the mass of wine — the effect is due to a
sudden diminution of the atmospheric pressure, as in
times of storm, for example. As the wine is always
charged with carbonic acid gas, which it holds in
solution from the moment of fermentation, one can
conceive that a lowering of barometric pressure would

STUDIES ON WINE. 117

cause the escape of some bubbles of carbonic acid.
These bubbles, rising from the lower part of the cask,
may disturb a portion of the deposit, which then mixes
with the wine and renders it turbid. But the real
cause of the disease is quite different. The turbidity
is without exception due to the presence of little fila-
ments of an extreme tenuity, about a thousandth part
of a millimeter in diameter. Their length is very
variable. It is these which, when the wine is agitated,
give rise to the silky waves just referred to. Often the
deposit of the casks leaves a swarm of these filaments
entangled in each otheij, forming a glutinous mass,
which under the microscope is seen to be composed
entirely of these little filaments. In acting upon
certain constituents of the wine, particularly upon the
tartar, this ferment generates carbonic acid. The
phenomenon of spurting is then produced, because
when the cask is closed the internal pressure of the
liquid augments. The sparkling and the crown of
little gas-bubbles, observed when the turned wine is
poured out into a glass, is similarly explained. In
a word, the disease of turned wine is nothing else
than a fermentation, due to an organised ferment
which, without any doubt, proceeds originally from
germs existing on the surface of the grapes at the
moment of gathering them, or on spoilt grapes such
as are found in every vintage. It is very rare
not to find this parasite of turned wine in the de-

118 LOUIS PASTEUK.

posit of the wine at the bottom of the casks, but
the parasite is not troublesome unless it multiplies
very largely. Pasteur found the means of prevent-
ing this multiplication by a very simple remedy,
equally applicable to other diseases of wines, such
as that of bitterness or greasiness (maladie de la
graisse).

Many wines acquire with age a more or less bitter
taste, sometimes to a degree which renders them
unfit for consumption. Bed wines, without exception,
are subject to this disease. It attacks by preference
wines of the best growth, and particularly the finest
wines of the Cote-d'Or. It is once more a little fila-
mented fungus which works the change ; and not
onlyjdoes it cause in the wine a bitterness which little
by little deprives it of all its better qualities, but it
forms in the bottles a deposit which never adheres
to the glass, but renders the wine muddy or turbid.
It is in this deposit that the filaments of the fungus
float. If white wines do not suffer from this disease
of bitterness, they are exposed, particularly the white
wines of Orleans and of the basin of the Loire, to the
disease of greasiness. The wines lose their limpidity ;
they become flat and insipid and viscous, like oil when
poured out. The disease declares itself in the casks or
in the best-corked bottles. M. Pasteur has discovered
that the greasiness of wines is likewise produced by a
special ferment, which the microscope shows to be

STUDIES ON WINE. 119

formed of filaments, like the ferments of the preceding
diseases, but differing in structure from the other
organisms, and in their physiological action on the
wine.

In short, according to Pasteur's observations, the\
deterioration of wines should not in any case be attri- \
buted to a natural working of the constituents of the I
wine, proceeding from a sort of interior spontaneous
movement, which would only be affected by varia- J
tions of temperature or atmospheric pressure. They
are, on the contrary, exclusively dependent on the
development of microscopic organisms, the germs of
which exist in the wine from the moment of the
original fermentation which gave it birth. What vast
multitudes of germs of every kind must there not be
introduced into every vintage tub ! What modifica-
tions do we not meet with in the leaves and in the
fruit of each individual spoilt vine ! How numerous
are the varieties of organic dust to be found on the
stems of the bunches, on the surface of the grapes, on
the implements of the grape gatherers ! What varieties
of moulds and mildews ! A vast proportion of these
germs are evidently sterilised by the wine, whose com-
position, being at the same time acid, alcoholic, and
devoid of air, is so little favourable to life. But is it
to be wondered at that some of these exterior germs,
so numerous, and possessing in a more or less marked
degree the anaerobic character, should find at certain

120 LOUIS PASTEUK.

moments, in the state of the wine, the right conditions
for their existence and multiplication ?

The cause of these alterations having been found, a
mode of preventing the development of all these para-
sites had still to be sought. Pasteur's first endeavour
was to discover some substance which would be anta-
gonistic to the life of these ferments of disease, while
harmless to the wine itself, and devoid of any special
smell or taste. But in this research success was
dependent on too many conditions to be easily attain-
able. After some fruitless trials, the thought occurred
to Pasteur of having recourse to heat. He soon
ascertained that, to secure wine from all ulterior
changes, it sufficed to raise it, for some instants
only, to a temperature of from fifty-five to sixty
degrees. His experiments were first directed upon
the disease of ' bitterness.' He procured some of the
best wines of Burgundy, wines of Beaune, and of
Pomard, of different years— 1858, 1862, and 1863.
Twenty-five bottles were left standing forty- eight
hours to allow all the particles suspended in the wine
to settle ; for, however clear wine may be, it always
produces a slight deposit. Pasteur then decanted the
wine with minute care, by means of a syphon of slow
delivery. This last precaution was necessary to pre-
vent the deposit from being stirred up. When there
remained in each bottle only one cubic centimeter of

STUDIES ON WINE. 121

liquid, Pasteur shook the bottle, and then examined
with the microscope the residue of each bottle. He
perceived in each case distinct filaments of ferment.
The wines, however, were not in the least bitter to
the taste, but the germs of a possible evil were there
— an evil which would have been first detected by the
palate when the little fungus had fully developed.

Without uncorking it, Pasteur then heated a
bottle of each of these wines. The heating was carried
to a temperature of sixty degrees (140° Fahr.). After
the cooling of the bottles he laid them by the side of
other unheated bottles of the same wines in a cellar,
the temperature of which varied in summer between
thirteen and seventeen degrees. Every fifteen days
Pasteur inspected them. Without uncorking the
bottles, he held them up against the light, so that he
could see the sediment at the bottom of each bottle,
and thus detect the least formation of deposit. In less
than six weeks, particularly in the wine of 1863, a
very perceptible floating deposit began to form in all the
unheated bottles. These deposits gradually augmented,
and on examining them with the microscope they were
seen to be formed of organised filaments, mixed some-
times with a little colouring matter which had become
insoluble. No deposit appeared in the heated bottles.

The idea of heating wines does not belong to
Pasteur. Those who love to search into questions of

122 LOUIS PASTEUK.

priority will find described in the works of Latin
agriculturists various methods for the preservation
of wine, based on the employment of heat. To give
the wine durability, they sometimes added to the
vintage variable quantities of boiled must, reduced to
half or two thirds, in which orris, myrrh, cinnamon,
white resin, and other ingredients, were infused. But,
to cite examples nearer our own time, Appert, whose
preserves have become so popular, relates that he sent
to St. Domingo some bottles of Beaune which had
been previously heated to seventy degrees, and that
he compared, on their return into France, two bottles
of this wine with a bottle which had remained at
Havre, and also with other bottles of the same wine
which had remained in his cellar, neither of which had
undergone the operation of heating. The superiority
of the wine which came from St. Domingo, said
Appert, was incontestable. Nothing could equal its
delicacy or its perfume. But Appert did not by any
means describe the wine of the two bottles which re-
mained in France as either injured or diseased. His
remark was based upon an incomplete observation.
It simply stated the fact, which indeed was previously
known, that a long voyage, added to the employment of
heat, had an excellent effect upon the Beaune. This in-
cident had been so completely forgotten, that it was only
in 1865 that Pasteur, during the historical researches
which preceded his 'Etudes sur le vin,' accidentally

STUDIES ON WINE. 123

met with this story of the bottles of St. Domingo, and
hastened to communicate it to the Academy. But
in reference to this question of heating, a discussion
arose as to priority, which was quite unexpected by
him. A Burgundian wine grower, M. cle Vergnette,
having first proposed the congealing of wines as a pro-
tective influence, had afterwards spoken, without much
precision, of heat as another means of preservation.
On this ground he claimed for himself a great part of
the invention of Pasteur's process. ' If, after having
subjected some specimens of wines which are to be sent
abroad to the ordeal of heating,' said M. de Vergnette,
' one sees that they have been able to resist the action
of the heat, then they may safely be shipped. In the
contrary case they ought not to be sent.' According to
M. de Vergnette, it was to the composition of the wine,
its robust condition, and good constitution, that it
owed its power of supporting the heating process.
Pasteur had no difficulty in demonstrating that these
.assertions are contradicted by experiment. Wine
never changes by the moderate application of heat
when air is excluded ; and it is precisely when of
doubtful soundness that it should be subjected to the
process of heating. This operation does not alter it
any more than would be the case if it were in a perfectly
healthy state. All wines may undergo the action of
heat without the least deterioration, and one minute's
heating at the proper temperature suffices to insure

124 LOUIS PASTEUE.

the preservation of every kind of wine. Thanks to
this operation, the weakest wine, the most disposed to
turn sour, to become greasy, or to be threatened with
bitterness, is insured against injurious change.

Nothing is more simple than to realise the con-
dition of heating in bottles. After having firmly tied
down the corks, the bottles are placed in a water-bath.
An iron basket is here useful. The water ought to
rise up to the wire of the cork. Among these bottles
is placed a bottle of water, into which the bulb of a
thermometer is plunged. The bath being heated, as
soon as the thermometer marks fifty or sixty degrees
Centigrade, the basket is withdrawn. The subsequent
soundness of the wine is thus insured.

But if Pasteur had overlooked nothing in his efforts
to prevent or arrest the evil changes of wine, he still
saw that full confidence was not felt in the efficacy of a
process which must, it was thought, damage the taste,
or the colour, or the limpidity of the wine. After
having invited the judgment of people in society, whose
preference, if they felt any, was generally for the heated
wines, Pasteur wished to have a more decisive opinion.
He addressed himself first to wine merchants and
others practised in detecting the smallest peculiarities
of wines ; and afterwards he organised a grand experi-
ment in tasting. On November 16, 1865, a sub-com-
mission, nominated by the representative commission
of the wholesale wine-sellers of Paris, repaired to the

STUDIES ON WINE. 125

Ecole Normale and examined a considerable number
of specimens. After a series of tastings, which recog-
nised, if not a superiority over the heated wines, at least
a shade of imperceptible flavour, which, however, it
was admitted, would escape nine-tenths of the con-
sumers, Pasteur, fearing that there remained still in
the mind of the majority of the commission a slight
prejudice against the operation of heating, and that
imagination, moreover, had some share in deter-
mining shades of flavour, proposed that at the next
sitting there should be no indication which of the
samples of wine had been heated and which had not.
The commission, having no other desire than to arrive
at the truth, at once accepted this proposition.

The resulting uncertainty as to whether the heated
or the unheated wines were to be preferred was so abso-
lute as to be comical. It is unnecessary to say that the
heated wines had not experienced the least alteration.
At a certain point Pasteur, who was astonished at the
extraordinary delicacy of the palate of these tasters,
employed a little trickery. He offered them two speci-
mens absolutely identical, taken out of the same bottle.
There were preferences, very slight it is true, but pre-
ferences gravely expressed for one or the other glass.
The commission, making allusion in its report to this
special tasting experiment, was the first to allow with
a good grace that the differences between the heated
and non-heated wines were insignificant, imperceptible

126 LOUIS PASTEUR.

if they existed, and that the imagination — added the
report — was not without considerable influence in the
tasting, since the members of the commission had
themselves fallen into a little experimental snare.

Thus Pasteur, after having revealed the causes
which determine the alterations of wines, had found
the means of practically neutralising them. By the
application of heat, and without producing any change
in the colour or flavour of the wines, he had been able to
insure their limpidity, and to render them capable of
being indefinitely preserved in well-closed vessels. If
these wines, being afterwards exposed too long to the
air, were again threatened with alteration, it was be-
cause the air brought to them new living germs of
those ferments which had been destroyed by the heat.
But germs from this source are so trifling compared
with those contained in the wine itself, that one may
almost say the heating process renders the wine un-
alterable even after it has been rebottled in contact
with the air. Thus, by a series of experiments which
left nothing to chance, one of the greatest economic
questions of the day was solved. Wines could be
kept or transported into all countries without losing
their flavour or their perfume. These experiments of
the laboratory were destined to have an extensive
application ; for very soon arrangements were made
for heating wine in barrels, the inquiry thereby as-
suming the proportions of a public benefit.

12'

THE SILKWORM-DISEASE.

THE life of the population of certain departments
in the South of France hangs on the existence of
silkworms. In each house there is nothing to be seen
but hurdles, over which the worms crawl. They are
placed even in the kitchens, and often in well-to-do
families they occupy the best rooms. In the largest
cultivations, regular stages of these hurdles are raised
one above the other in immense sheds, under roofs of
disjointed tiles, where thousands and thousands of
silkworms crawl upon the litters which they have the
instinct never to leave. Great or small, the silkworm-
rearing establishments exist everywhere. When people
accost each other, instead of saying ' How are you ? '
they say ' How are the silkworms ? ' In the night they
get up to feed them or to keep up around them a
suitable temperature. And then what anxiety is
felt at the least change of weather! Will not the
mulberry leaves be wet ? Will the worms digest well ?
Digestion is a matter of great importance to the health
of the worms, which do nothing all their lives but eat !

128 LOUIS PASTEUR.

Their appetites become especially insatiable during
the last clays of rearing. All the world is then astir,
day and night. Sacks of leaves are incessantly
brought in and spread out on the litters. Sometimes
the noise of the worms munching these leaves resembles
that of rain falling upon thick bushes. With what
impatience is the moment waited for when the worms
arrive at the last moulting ! Their bodies swollen
with silk, they mount upon the brambles prepared
for them, there they shut themselves up in their golden
prisons and become chrysalides. What days of rejoicing
are those in which the cocoons are gathered ; when,
to use the words of Olivier de Serres, the silk harvest
is garnered in !

Just as in all agricultural harvests, this ingather-
ing of the silk is exposed to many risks. Nearly
always, however, it pays the cultivator for his trouble,
and sometimes pays him largely. But in 1849, after
an exceptionally good year, and without any atmo-
spheric conditions to account for the fact, a number
of cultivations entirely broke down. A disease which
little by little took the proportions of an epidemic
fell upon the silkworm nurseries. Worms hardly
hatched, and worms arrived at the last moulting, were
equally stricken in large numbers. It mattered little
in what phase the silkworm happened to be : in all it
was assailable by the evil.

There is hardly a schoolboy who has not reared in

THE SILKWORM-DISEASE. 129

the recesses of his desk some five or six silkworms, feed-
ing them, in default of mulberry leaves, with leaves of
lettuce or salsify. Therefore it is hardly necessary to
remind my readers how the silkworm is born, grows,
and is transformed. Coming out of its egg, which is
called a grain, because of its resemblance to a small
vegetable seed, the silkworm appears in the first fine
days of spring. It does not then weigh more than
one or two milligrammes. Little by little its size and
its activity augment. The seventh day after its birth
it rests on a leaf and appears to sleep. It remains
thus for nearly thirty hours. Presently, its head
moves, as if it did not belong to the rest of the body,
and under the skin of this head appears a second
quite new head. Just as if it came out of a case, the
silkworm disengages itself from its old withered skin.
Here are its front feet, there the false feet (faussespattes),
which it carries behind. At length the worm is quite
complete. It rests a while and then begins to eat.
At the end of a few days new sleep, new skin, new
shedding of the skin, then a third, and then a fourth
metamorphosis. About eight days after the fourth
shedding of its skin, the worm ceases to eat, its body
becomes more slender, more transparent ; it seeks to
leave its litter, it raises its head and appears uneasy.
Some twigs of dried heather are then arranged for
it to fasten upon ; these it climbs, never to descend
again. It spins its cocoon and becomes a chrysalis.

K

130 LOUIS PASTEUR.

When the worms of a cultivation have all spun
their cocoons, they are smothered in a steam stove,
and, after being dried in the sun, they are handed
over to the spinners. If it is desired to reserve some
of the cocoons for seed, instead of being smothered,
they are strung together in chaplets. After about
three weeks, the moth comes out of its chrysalis. It
pierces the cocoon by means of a liquid which issues
from its mouth, and which has the property of so
softening the silk that the moth is able to pass through
the cocoon. It has hardly dried itself and developed
its wings when the males and females pair for several
hours. Then the females lay their eggs, of which they
can produce from four to six hundred. These are all
the phases through which silkworms pass in the space
of two months.

In the epidemic which ravaged the silkworm nur-
series in 1849 the symptoms were numerous and
changeable. Sometimes the disease exhibited itself
immediately. Many of the eggs were sterile, or the
worms died during the first days of their existence.
Often the hatching was excellent, and the worms ar-
rived at their first moulting, but that moulting was a
failure. A great number of the worms, taking little
nourishment at each repast, remained smaller than
the others, having a rather shining appearance and a
blackish tint. Instead of all the worms going through

THE SILKWORM-DISEASE. 131

the phases of this first moulting together, as is usually
the case in a batch of silkworms, they heganto present a
marked inequality, which displayed itself more and more
at each successive moulting. Instead of the worms
swarming on the tables, as if their number was uniformly
augmenting, empty spaces were everywhere seen ;
every morning corpses were collected on the litters.

Sometimes the disease manifested itself under still
more painful circumstances. The batch would pro-
gress favourably to the third, and even to the fourth
moulting, the uniform size and the health of the
worms leaving nothing to be desired ; but after the
fourth moulting the alarm of the husbandman began.
The worms did not turn white, they retained a rusty
tint, their appetite diminished, they even turned
away from the leaves which were offered to them.
Spots appeared on their bodies, black bruises irregu-
larly scattered over the head, the rings, the false feet,
and the spur. Here and there dead worms were
to be seen. On lifting the litter, numbers of corpses
would be found. Every batch attacked was a lost
batch. In 1850 and 1851 there were renewed failures.
Some cultivators, discouraged, attributed these acci-
dents to bad eggs, and got their supplies from abroad.

At first everything went as well as could be
wished. The year 1853, in which many of these
eggs were reared in France, was one of the most
productive of the century. As many as twenty-six

K 2

132 LOUIS PASTEUE.

millions of kilogrammes of cocoons were collected,
which produced a revenue of 130,000,000 francs.
But the year following, when the eggs produced by
the moths of these fine crops of foreign origin were
tried, a singular degeneracy was immediately recog-
nised. The eggs were of no more value than the French
eggs. It was in fact a struggle with an epidemic.
How was it to he arrested ? Would it be always
necessary to have recourse to foreign seed ? and
what if the epidemic spread into Italy, Spain, and the
other silk cultivating countries ?

The thing dreaded came to pass. The plague
spread; Spain and Italy were smitten. It became
necessary to seek for eggs in the Islands of the
Archipelago, in Greece, or in Turkey. These eggs, at
first very good, became infected in their turn in their
native country ; the epidemic had spread even to that
distance. The eggs were then procured from Syria
and the provinces of the Caucasus. The plague
followed the trade in the eggs. In 1864 all the culti-
vations, from whatever corner of Europe they came,
were either diseased or suspected of being so. In the
extreme East, Japan alone still remained healthy.

Agricultural societies, governments, all the world
was preoccupied with this scourge and its invading
march. It was said to be some malady like cho-
lera which attacked the silkworms. Hundreds of
pamphlets were published each year. The most

THE SILKWOEM-DISEASE. 133

foolish remedies were proposed, as quite infallible —
from flowers of sulphur, cinders, and soot spread over
the worms, or over the leaves of the mulberry, to
gaseous fumigations of chlorine, of tar, and of sul-
phurous acid. Wine, rum, absinthe, were prescribed
for the worms, and after the absinthe it was advised
to try creosote and nitrate of silver. In 1863 the
Minister of Agriculture signed an agreement with an
Italian who had offered for purchase a process destined
to combat the disease of the silkworms, by which
he (the Minister) engaged himself, in case the efficacy
of the remedy was established, to pay 500,000 francs
as an indemnity to the Italian silk cultivator. Ex-
periments were instituted in twelve departments, but
without any favourable result. In 1865 the weight
of the cocoons had fallen to four million kilogrammes.
This entailed a loss of 100,000,000 francs.

The Senate was assailed by a despairing petition
signed by 3,600 mayors, municipal councillors, and
capitalists of the silk-cultivating departments. The
great scientific authority of M. Dumas, his knowledge
of silk husbandry, his sympathy for one of the depart-
ments most severely smitten, the Gard, his own native
place, all contributed to cause him to be nominated
Reporter of the Commission. While drawing up his
report the idea occurred to him of trying to persuade
Pasteur to undertake researches as to the best means
of combating the epidemic.

134 LOUIS PASTEUR.

Pasteur at first declined this offer. It was at the
moment when the results of his investigations on
organised ferments opened to him a wide career ; it
was at the time when, as an application of his latest
studies, he had just recognised the true theory of the
fabrication of vinegar, and had discovered the cause of
the diseases of wines; it was, in short, at the moment
when, after having thrown light upon the question of
spontaneous generation, the infinitely little appeared
infinitely great. He saw living ferments present every-
where, whether as agents of decomposition employed to
render back to the atmosphere all that had lived, or
as direct authors of contagious maladies. And now
it was proposed to him to quit this path, where his
footing was sure, which offered him an unlimited
horizon in all directions, to enter on an unknown
road, perhaps without an outlet. Might he not expose
himself to the loss of months, perhaps of years, in
barren efforts ?

M. Dumas insisted. ' I attach,' said he to his old
pupil, now become his colleague and his friend, * an
extreme value to your fixing your attention upon
the question which interests my poor country. Its
misery is beyond anything that you can imagine.'

' But consider,' said Pasteur, * that I have never
handled a silkworm.'

* So much the better,' replied M. Duinas. ' If you
know nothing about the subject, you will have no

THE SILKWORM-DISEASE. 135

other ideas than those which come to you from your
own observations.'

Pasteur allowed himself to be persuaded, less by the
force of these arguments than by the desire to give
his illustrious master a proof of his profound deference.

As soon as the promise was given and the resolu-
tion made to go to the South, Pasteur thought over
the method to be employed in the pursuit of the
problem. Certainly, amidst the labyrinth of facts and
opinions, it was not hypotheses which were wanting.
For seventeen years they had been rising up on all
sides.

One of the most recent and the most comprehen-
sive memoirs upon the terrible epidemic had been
presented to the Academy of Sciences by M. de Quatre-
fages. One paragraph of this paper had forcibly
struck Pasteur. M. de Quatrefages related that some
Italian naturalists, especially Filippi and Cornalia,
had discovered in the worms and moths of the silk-
worm minute corpuscles visible only with the
microscope. The naturalist Lebert affirmed that
they might always be detected in diseased silkworms.
Dr. Osimo, of Padua, had even perceived corpuscles
in some of the silkworms' eggs, and Dr. Vittadini had
proposed to examine the eggs with a microscope in
order to secure having sound ones. M. de Quatre-
fages only mentioned this matter of the corpuscles as

136 LOUIS PASTEUK.

a passing remark, being doubtful of its importance,
and perhaps of its accuracy. This doubt might have
removed from Pasteur's mind the thought of examining
the significance of these little corpuscles, but, amid the
general confusion of opinions, Pasteur was attracted to
the study of these little bodies all the more readily
because it related to an organic element which was
visible only with the microscope. This instrument
had already rendered such services to Pasteur in his
delicate experiments on ferments, that he was fasci-
nated by the thought of resuming it again as a means
of research.

I.

On June 6, 1865, Pasteur started for Alais. The
emotion he felt on the actual spot where the plague
raged in all its force, in the presence of a problem
requiring solution, caused him at once to forget the
sacrifices he had made in quitting his laboratory at
the Ecole Nor male. He determined not to return to
Paris until he had exhausted all the subjects requiring
study, and had triumphed over the plague.

In a few hours after his arrival he had already
proved the presence of corpuscles in certain worms,
and was able to show them to the President and
several members of the Agricultural Committee, who
had never seen them.' The following day he installed

THE SILKWORM-DISEASE. .137

himself in a little house three kilometers from Alais.
Two small cultures were there going on ; they were
nearly the last, the cocoons had all been spun. One
of these cultures, proceeding from eggs imported that
very year from Japan, had succeeded very well. The
other, proceeding also from Japanese eggs which had
been reproduced in the country, had arrived at their
fourth moulting and had a very bad appearance.
But, strange to say, on examining with the microscope
a number of chrysalides and moths of the group which
had so delighted its proprietor, Pasteur found cor-
puscles almost always present, whereas the examina-
tion of the worms of the bad group only exhibited
them occasionally. This double result struck Pasteur
as very strange. He at once sent messengers into all
the neighbourhood of Alais to seek for the remains of
backward cultivations. He attached extreme impor-
tance to ascertaining whether the presence of corpus-
lies in the chrysalides or moths of the good groups, and
the absence of the same corpuscles in the worms of the
bad groups, was an accidental or a general fact. He
soon recognised that these results did very frequently
Dccur. But what would happen when the worms of
jhe bad group spun their cocoons? ' Pasteur found
ihat in the chrysalides, especially in the old ones, the
corpuscles were numerous. As regards the moths
)roceeding from these cocoons, not one was free from
ihem, and they existed in profusion.

138 LOUIS PASTEUR.

Following up the idea that a connection between
the disease and the corpuscles might possibly exist,
as other observers had previously imagined, Pasteur
declared, in a Note presented to the Agricultural
Committee of Alais on June 26, 1865, twenty days
after his arrival, that it was a mistake to seek for the
corpuscle in the eggs or in the worms. Both the one
and the other could carry in them the germ of the
disease, without exhibiting distinct corpuscles, visible
under the microscope. The evil developed itself espe-
cially in the chrysalides and in the moths, and it was
in them that search should be made. Finally, Pasteur
came to the conclusion that the only infallible method
of procuring healthy eggs must be by having recourse
to moths free from corpuscles.

Pasteur hastened to apply this new method of ob-
taining pure eggs. Notwithstanding that the malady
was universally prevalent, he succeeded, after several
days of assiduous microscopic observations, in finding
some moths free from corpuscles. He carefully pre-
served their eggs, as well as other eggs which had
proceeded from very corpusculous couples, intending to
wait for what these eggs would produce the following
year ; the first would be probably free from corpuscles,
while the latter would contain them. He would thus
have in future, though on a small scale, samples of
originally healthy and of originally unhealthy cultiva-
tions, by the comparison of which with the cultivations

THE SILKWOEM-DISEASE. 139

of the trade — all more or less smitten with the evil —
totally new views might be expected to emerge. Who
can tell, thought Pasteur, whether the prosperity of
the silk cultivation may not depend on the practical
application of this production of pure eggs by means
of moths free from corpuscles ?

Scarcely had Pasteur made known, first to the
Committee of Alais, and then to the Academy of
Sciences, the results of his earliest observations and
the inductions to which they pointed, when critics
without number arose on all sides. It was objected
that the labours of several Italian savants had
established beyond all doubt that the corpuscles were
a normal element of certain worms, and especially of
all the moths when old; that other authors had
affirmed it to be sufficient to starve certain worms to
make these famous corpuscles appear in all their
tissues ; and that Dr. Gaetano Cantoni had already
tried some cultivations with eggs coming from moths
without corpuscles, and that he had totally failed.

' Your efforts will be vain,' wrote the celebrated
Italian entomologist Cornalia ; ' your selected eggs will
produce healthy worms, but these worms will become
sickly through the influence of the epidemic demon
which reigns everywhere.'

Anyone but Pasteur would have been staggered,
but he was not the man to allow himself to be dis-

140 LOUIS PASTEUR

couraged by a priori opinions, and by assertions which
were more or less guesswork. He was resolved not to
abandon his preconceived idea until experiment had
pronounced upon it with precision. All scientific re-
search, in order to be undertaken and followed up
with success, should have, as point of departure, a
preconceived idea, an hypothesis which we must seek
to verify by experiment. To judge of the value of
the facts which Pasteur had just announced, it was
necessary to know if there existed the relation of cause
and effect between the corpuscles and the disease.
This was the great point to be elucidated.

But if, without preliminary groping, he had dis-
covered the way to be pursued, Pasteur subsequently
brought to bear his rare prudence as an experimen-
talist. For five years he returned annually for some
months to Alais. The little house nestling among
the trees called Pont-Guisquet became at the same
time his habitation and his silkworm nursery. It is
hemmed in by mountains, up the sides of which ter-
races rise, one above the other, planted with mulberry
trees. The solitude was profound. Madame Pasteur
and her daughter constituted themselves silkworm-
rearers — performing their part in earnest, not only
gathering the leaves of the mulberry trees, but also
taking part in all the experiments. The assistants
of the Ecole Normale, Duclaux, Maillot, Gernez,

THE SILKWORM-DISEASE. 141

and Eaulin, grouped themselves around their master.
Thus, in an out-of-the-way corner of the Cevennes
was formed a colony seeking with ardour the solution
of an obscure problem, and the means of curing or
preventing a disease which had for so long a time
blighted one of the great sources of the national
wealth.

One of the first cares of Pasteur was to settle the
question as to the contagion of the disease. Many
hypotheses had been formed regarding this contagion,
but few experiments had been made, and none of
them were decisive. Opinions were also very much
divided. Some considered that contagion was cer-
tain ; the majority, however, either doubted or denied
its existence ; some considered it as accidental. It was
said, for example, that the evil was not contagious by
itself, but that it became so through the presence and
complication of other diseases which were themselves
contagious. This hypothesis was convenient, and it
enabled contradictory facts to be explained. If some
persons had seen healthy worms, which had been
mixed up either by mistake or intention with sickly
ones, perish, and if they insisted on contagion,
others forthwith replied by diametrically opposite
observations.

But whatever the divergences of opinion might
be, everyone at all events believed in the existence of
a poisonous medium rendered epidemic by some occult

142 LOUIS PASTEUR,

influence. Pasteur soon succeeded, by accurate ex-
periments, in proving absolutely that the evil was
contagious.

One of the first experiments was as follows. After
their first moulting, he took some very sound worms
free from corpuscles, and fed them with corpusculous
matter, which he prepared in the following simple
manner. He pounded up a silkworm in a little water,
and passed a paint-brush dipped in this liquid over
the whole surface of the leaves. During several days
there was not the least appearance of disease in the
worms fed on those leaves ; they reached their second
moulting at the same time as the standard worms
which had not been infected. The second moulting
was accomplished without any drawback. This was
a proof that all the worms, those infected as well as
the standard lot, had taken the same amount of
nourishment. The parasite was apparently not pre-
sent. Matters remained in this state for some days
longer. Even the third moulting was got through
without any marked difference between the two groups
of worms. But soon important changes set in. The
corpuscles, which had hitherto only showed themselves
in the integuments of the intestines, began to appear
in the other organs. From the second day follow-
ing the third moulting — that is to say, the twelfth
after the infection — a visible inequality distinguished
the infected from the non-infected worms. Those

THE SILKWORM-DISEASE. 143

of the standard lot were clearly in much the best
health. On examining the infected worms through
a magnifying glass, a multitude of little spots were
discovered on their heads, and on the rings of their
bodies, which had not before shown themselves. These
spots appeared on the exterior skin when the interior
skin of the intestinal canal contained a considerable
number of corpuscles. It was these corpuscles that
impeded the digestive functions, and interfered with
the assimilation of the food. Hence arose the in-
equality of size of the worms. After the fourth moult-
ing, the same type of disease was noticed as that
which was breaking out everywhere in the silkworm
nurseries, especially the symptom of spots on the
skin, which had led to the disease being called pebrine.
The peasants said that the worms were peppered.
The majority of the worms were full of corpuscles.
Those which spun their cocoons produced chrysalides
which were nothing but corpusculous pulp, if such
a term be allowed.

It was thus proved that the corpuscles, introduced
into the intestinal canal at the same time as the food
of the worms, convey the infection into the intestinal
canal, and progressively into all the tissues. The
malady had in certain cases a long period of incuba-
tion, since it was only on the twelfth day that it be-
came perceptible. Finally, the spots of pebrine on
the skin, far from being the disease itself, were but

144 LOUIS PASTEUR,

the effect of the corpuscles developed in the interior ;
they were but a sign, already removed from the true
seat of the evil. ' If these spots of pebrine,' thought
Pasteur, * were considered in conjunction with certain
human maladies in which spots and irruptions appear
on the body, what interesting inductions might pre-
sent themselves to minds prepared to receive them ! '

Pasteur was never tired of repeating this curious
experiment, or of varying its conditions. Sometimes
he introduced the corpusculous food into healthy
worms at their birth, sometimes at the second or
third moulting. Occasionally, when the worms were
about to spin their cocoons, the corpusculous food was
given them. All the disasters that were known to
have happened in the silkworm nurseries, their extent
and their varied forms, were faithfully reproduced.
Pasteur created at will any required manifestation of
pebrine. When he infected quite healthy worms, after
their fourth moulting, with fresh corpusculous matter,
these worms, even after several meals of corpusculous
leaves alternated with meals of wholesome leaves,
made their cocoons. It might have been supposed
that in this case the contagion had not taken effect.
This was but a deceptive appearance. The communi-
cation of the disease exhibited itself in a marked de-
gree in the chrysalides and in the moths. Many of
the chrysalides died before they turned into moths,
and their bodies might be said to be entirely composed

THE SILKWORM-DISEASE. 145

of corpuscles. Such moths as were formed, and which
emerged from their cocoons, had a most miserable ap-
pearance. The disease sometimes went so far as to
render breeding and the laying of eggs impossible.

Faithful to the rules prescribed by the experi-
mental method, Pasteur was careful to reproduce
these same experiments with the worms of the
standard lot, from which all infected worms had
been selected. He fed these healthy worms on leaves
over which a clear infusion made from the remains of
moths or worms exempt from corpuscles had been
spread with a paint-brush, instead of leaves conta-
minated with corpusculous remains. This food kept
the worms in their usual health. Could there be a
better proof that the corpuscles alone were the real
cause of the pebrine disease?

These experiments, I repeat, threw a strong light
on the nature of the disease, and exactly accounted
for what took place in the industrial cultivations.
From the malady which attacked the worms at their
birth, decimating a whole cultivation, down to the
invisible disease that may be said to inclose itself
in the cocoon, all was now explained. One of the
effects of the plague which had most excited the sur-
prise and thwarted the efforts of cultivators was the
impossibility of finding productive eggs, even when
they tried to obtain them from the cocoons of groups
which had succeeded perfectly well as far as the pro-

L

146 LOUIS PASTEUK.

duction of cocoons was concerned. It was proved
that almost invariably the following year the eggs of
these fine-looking groups were unproductive. Num-
bers of the agricultural boards, and practitioners, not
being able to believe in the existence of the disease in
collections that were so satisfactory as regards the
abundance and beauty of the cocoons, persisted in
thinking that the failures had an origin not connected
with the seed itself. This resulted in deception after
deception, often even in mistakes that were much to
be regretted. Frequently the best husbandmen were
known to reserve for the production of eggs some
very fine cultivations, not having observed in the
worms either spots of pelrine or corpuscles even up
to the time when the mounting of the brambles had
been accomplished; and the year following they had
the pain of seeing all the cultivations from these eggs
perish. These circumstances, so well calculated to
produce discouragement and to give the disease a
mysterious character, met with their natural explana-
tion in the facts proved by experimental infection.

Still, as it never occurs to the cultivator to infect
the worms directly by giving them food charged with
corpusculous debris, it might be asked how, in the
industrial establishments, such results can be pro-
duced. Pasteur lost no time in solving this difficulty.

In a cultivation containing corpusculous worms
these worms perpetually furnish contagious matter,

THE SILKWORM-DISEASE. 147

which falls upon the leaf and fouls it. This is the
excreta of the worms, which the microscope shows to
be more or less filled with corpuscles drawn from the
lining of the intestinal canal. It is there that they
swarm. It is easy to understand that these excreta,
falling on the leaves, contaminate them all the more
easily because the worms, by the weight of their bodies
in crawling, press the excreta against the leaves.
This is one cause of natural contagion. By the ex-
creta of corpusculous worms which he crushed, mixed
with water, and spread with a paint-brush over the
mulberry leaves intended for a single meal, Pasteur
was able to communicate the contagion to as many
worms as he liked.

He also indicated another natural and direct cause
of contagion. The six fore-feet of the worm have
sharp hooks at their ends, by means of which the
worms prick each other's skins. Let any one imagine
3, healthy worm passing over the body of the corpus-
culous worm. The hooks of the first worm, by pene-
trating the skin of the second, are liable to be soiled
by the corpuscles immediately below that skin ; and
these hooks are capable of carrying the seeds of dis-
ease to other healthy worms, which may be pricked in
their turn. To demonstrate experimentally, as Pas-
teur did, the existence of this cause of contagion, it
was only necessary to take some worms and allow
them to wound each other. Lastly, infection at a

L 2

148 LOUIS PASTEUK.

distance, through the medium of the air and the dust it
carries, is a fact equally well established. It is suffi-
cient, by sweeping the breeding-houses, or by shaking
the hurdles, to stir up the dust of corpusculous excre-
tions and the dried remains of dead worms, and to
allow them to be spread over the hurdles of the
healthy worms, to cause, after a certain time, con-
tagion to appear among these worms. When very
healthy worms were placed in a breeding nursery at a
considerable distance from unhealthy worms, they, in
their turn, became infected.

After so many decisive experiments it was no
longer possible not to see in pebrine an essentially
contagious disease. Nevertheless, among facts in-
voked in favour of non-contagion, there was one which
it was difficult to explain. There existed several
examples of successful cultivations conducted in
nurseries which had totally failed from the effects of
pebrine the year before. The explanation is, as shown
by Pasteur, that the dust can only act as a con-
tagion when it is fresh. Corpusculous matter, when
thoroughly dried, loses its virulence. A few weeks
suffice to render such matter inoffensive : hence the
dust of one year is not injurious to the cultivations of
the next year. The corpuscles contained in the eggs
intended for future cultivation alone cause the trans-
mission of the disease to future generations.

And what can be more easilv understood than the

THE SILKWOBM-DISEASE. 149

presence of corpusculous parasites in the egg ? The
egg comes into existence during that marvellous phase
of the life of a silkworm when, after having spun its
cocoon, it sleeps within it as a chrysalis, resolving itself,
so to speak, into those kinds of albumen and yelk
from which the fully-formed moth will emerge, as a
chick emerges from its egg. Let anyone imagine /
this origin of an approaching life, no longer in its j
normal purity, but associated with a parasite which
will find in the materials surrounding it, so adapted
to life and transformation, the elements of its own
nourishment and multiplication. This parasite will be
present when the eggs of the female moth, tender and
soft as albumen, begin to define their outlines. Woe ,
betide those eggs if they then enclose any particles of
corpuscle, or of its original matrix. In vain will the
envelope of those eggs become by degrees hard and
horny ; the enemy is within, and later on he will be
discovered in the embryo of the silkworm.

Thus this terrible plague is at the same time con-
tagious and hereditary, helping us to understand the
evolution of this double character in certain maladies
both of men and animals.

II.

The first time Pasteur went to Alais the silkworm
epidemic was universally attributed to a single cause
—pebrine. Pebrine was called the disease. This

150 LOUIS PASTEUK.

word expressed everything. It indicated the existence
of a mysterious scourge, the origin and nature of
which could not be traced, but which was ready to
fall upon all the establishments devoted to the nurture
of the worms. Whatever might happen, or whatever
might be the cause of ruin in a silkworm nursery, the
disease was held responsible. One of the most striking
proofs that the evil was attributed to pebrine alone is
found in the fact that a prize of 5,000 florins was
offered by the Austrian Government in 1868, as a
reward for the discovery of the best remedy for the
prevention and cure of pebrine — * the epidemic disease
which devastates the silkworm.'

A rapid glance at the principles which have just
been established suffices to show that pebrine might
now be regarded as vanquished. Pasteur had de-
monstrated that moths free from corpuscles never
produced a single corpusculous egg ; he had proved,
moreover, that eggs brought up in a state of isolation,
at a distance from contaminated eggs, produce no
worms, chrysalides, or moths which are corpusculous.
It was easy, therefore, to multiply cultivations free from
pebrine. The production of silk and the production of
eggs was thus secured. To make sure that the eggs
were pure it was only necessary to have recourse to
the microscopic examination of the moths which had
produced them. These observations might be made
by women, by young girls, even by children. It was.

THE SILKWORM-DISEASE. 151

sufficient to crush up a moth in a little water, and to
put a drop of this mixture under the microscope, to
see the corpuscles clearly, if they existed. It seemed,
then, that the plague was got rid of. But Pasteur was
not slow in recognising that the general belief in a
single malady could not be justified. If the experi-
ments of 1866 had demonstrated to him the full ex-
tent of the corpusculous malady, and had established
the principles of a treatment proper for its prevention,
the method he had adopted had also shown him that
pebrine was far from being the only cause from which
the silk culture suffered.

It was in 1867 that this result was obtained.
From an experimental point of view, that year counted
double for Pasteur. Influenced by a profound sym-
pathy for the misery which he had witnessed during
two successive years, and, at the same time, impatient
to find the cause of the scourge, Pasteur, in the
months of February, March, and April, in advance of
the great industrial cultivations, commenced a Series
of experiments on worms hatched by artificial heat,
and fed with mulberry leaves from a hothouse.

During these forced experiments Pasteur observed
that out of sixteen broods derived from non-corpus-
culous parents, fifteen succeeded, while the sixteenth
perished almost entirely between the fourth moulting
and the climbing on to the brambles. After having
exhibited a most healthful appearance, the worms died

152 LOUIS PASTEUR.

suddenly. In a cultivation of 100 worms, ten, fifteen,
twenty dead ones were picked up daily : these turned
black, and became putrid with extraordinary rapidity,
often within the space of twenty-four hours. Some-
times they were soft and flabby, like an empty,
crumpled intestine. Consulting the authors who had
written upon silkworms, Pasteur could not doubt that
he had before his eyes a characteristic specimen of the
disease called morts-flats, oiflaclieric. Not only were
these worms free from all pebrine spots, but no cor-
puscles were to be found in any part of their bodies.
A still more significant fact was, that corpuscles were
also absent from the chrysalides and the moths of
those few worms which were able to spin their cocoons.
Although this sample was confined to a single group
of eggs derived from parents free from corpuscles,
Pasteur continued to entertain doubts as to the exist-
ence of only a single disease, and also as to the neces-
sary connection of pebrine with flacherie.

These suspicions were confirmed by his cultiva-
tions of April and May. Numerous cases of flaclierie
presented themselves. Uncertainty was no longer
possible as to the mutual independence of the two
maladies — pebrine and flaclierie. The cultivations
most seriously invaded by the last-mentioned disease
came from eggs produced by parents free from cor-
puscles, and led on to reproducers also free from this
parasite. On visiting a multitude of industrial cultiva-

THE SILKWOKM-DISEASE. 153

tions, Pasteur discerned that what had passed in his
own laboratory was of very general occurrence, and
that, contrary to the received opinion, two distinct
maladies divided between them the cause of all the
misfortunes. Pebrine was evidently the most widely
spread, but flacherie had also its share, and a very
large share, in the calamity.

Here, once more, the microscope came to Pasteur's
assistance. If, at the period of the rearing of the
silkworms, when the mean temperature is always
rather high, some mulberry leaves are crushed in a
mortar and mixed with a little water, the liquid being
left to itself, in twenty- four hours it will be found
filled with microscopic organisms ; some motionless,
resembling little rods or spores joined end to end,
like strings of beads, others more or less active,
flexible, endowed with a sinuous movement like that
of the vibrios found in nearly all organic infusions in
process of decomposition. Whence come these micro-
scopic organisms ? The facts relating to spontaneous
generation indicate that the germs of these organisms
were on the surface of the pounded leaf, spread in the
form of dust over the instruments used to triturate
the leaf, possibly on the mortar, the pestle, or in the
water added to the pounded leaves.

It is a curious fact, that if the intestinal canal of
a worm in full process of digestion be opened, the
pounded leaf which fills it from one end to the other

154 LOUIS PASTE UK.

will not show microscopic organisms of any kind,
but only cells of parenchyma, green granules of the
chlorophyl of the leaf, and remains of the air-vessels
of the plant. Through the action of the liquids
secreted by the glands which line the integuments of
the intestinal canal, the germs of organisms are them-
selves digested or hindered in their development. The
digestive functions of silkworms are so active that
everything is carried away, destroyed in the same
manner as the leaves themselves.

But if from any cause the digestion of the worms
be impeded or suspended, then the germs introduced
with the food into the intestinal canal will give rise
to the multiplication of microscopic organisms which
are always found in the artificially bruised leaf when
mixed with a little water. How numerous are the
causes which may check this digestive function of the
worm — a function of such importance to a creature
which in the space of one month passes from the
weight of half a milligramme to that of five, six, seven,
or even eight grammes ! Pasteur proved that when-
ever a worm was attacked with flaclierie, it always had,
associated with the food in its intestinal canal, one or
other of the microscopic organisms which are in-
variably to be met with among crushed mulberry leaves.
Summing up in a kind of aphorism a series of ob-
servations, Pasteur observes : ' Every ver flat is one
which digests badly, and, conversely, every worm

THE SILKWOKM-DISEASE. 155

which digests badly is doomed to perish of flaclierie,
or to furnish a chrysalis and a moth the life of which,
through the injury produced by organised ferments,
is not normally perfected.'

Thus, as in the case of pebrine, the morbid sym-
ptoms of flacker ie are very variable. All depends on
the intensity of the evil — that is to say, on the abun-
dance and the nature of the parasites developed in the
intestinal canal, and also on the period in the life of
the worm when this fermentation begins to show itself.
The most dangerous of all these ferments are those of
the family of vibrios. If they exist in the first phases
of the life of the worm, it dies quickly and very soon
becomes putrid, sometimes resolving itself into an in-
fected pus. The disease often manifests itself in a
manner particularly distressing and disastrous to the
cultivator. The worms have presented the most beau-
tiful appearance up to the time of climbing the
heather. The mortality has scarcely been two or
three per cent., which is nothing ; the moultings have
been effected in a perfect manner, when suddenly,
some days after the fourth moulting, the worms be-
come languid, crawling with difficulty, and hesitating
to take the leaves which are thrown upon their
hurdles. If some few have mounted on to the heather,
they stretch themselves on the twigs, their bodies swollen
with food which they cannot digest. Sometimes they
remain there motionless till they die, or, falling, remain

156 LOUIS PASTEUK.

suspended only by their false feet. The few moths which
have succeeded in piercing their cocoons do not show
any corpuscles. They can produce eggs, but these
eggs, coming from parents weakened by disease, give
rise the following year to a generation threatened
with flacherie. It is in this sense that the disease
may be regarded as hereditary, although the para-
sites of the intestinal canal to which flacherie is due
do not transmit themselves to the eggs or to the
worms which issue from them. The worms inherit
weakly constitutions, and, being without power of
resistance against anything that can derange their
digestive functions, they are at the mercy of the
accidents of their culture.

Too large an assemblage of worms in one nursery ;
too high a temperature at the time of moulting; a
thunderous atmosphere, which predisposes organic
matter to fermentation ; the use of heated or wet
leaves, especially if the wetting be caused by a fog or
by the morning or evening dew, which deposits on the
leaf the germs suspended in a great mass of air ; — these
are so many causes calculated to diminish the activity
of the digestive functions of the worms, and to produce
in consequence a fermentation of the leaf in the in-
testinal canal — the malady now under consideration.
Often also flacherie depends upon mistakes committed
by the husbandman while tending his precious ' kine,'
to use an expression of the sixteenth century.

THE SILKWOEM-DISEASE. 157

A Chinese book published on the rearing of silk-
worms contains a series of little practical counsels.
* The person who takes care of the silkworms,' says
this guide to the perfect cultivator, ' ought to wearf a
simple garment, not lined. He must regulate the
temperature of the spinning-house according to the
sensation of heat or cold which he experiences ; if he
feels cold, he may conclude that the worms are cold,
and he will increase the fire ; if he feels hot, he will
conclude that the worms are hot, and he will suitably
diminish the fire.'

One point which had been ignored before the ex-
periments of Pasteur was the contagious character of
ftacherie. This contagion may surpass that of pelrine
itself as regards duration. In pebrine the dried cor-
pusculous matter loses all virulence after the lapse
of some weeks. The disease cannot, therefore, com-
municate itself from one year to another by the cor-
pusculous dust of a rearing establishment. The germs,
on the contrary, of the microscopic organisms which
provoke fermentation in the mulberry leaves, especially
the vibrios, retain their vitality for several years. The
dust of a silkworm nursery infected by flacherie ap-
pears under a microscope quite full of cysts or spores
of vibrios. These spores or cysts rest, like the sleep-
ing beauty in the forest, until a drop of water falls
upon them and awakens them into life. Deposited
on the leaves which are to serve as nourishment,

158 LOUIS PASTEUR.

these germs of vibrios are carried into the intestinal
canal of the worm, develop and multiply themselves,
and completely disturb the digestive functions, unless
the digestion is so strong that the germs are imme-
diately arrested, and disposed of like the food itself.
This is what happens when the worms are in full
vigour. It is a struggle for life, in which the worms
often gain the victory.

Giving to some very healthy worms a meal of
leaves covered with the dry dust of a silkworm
nursery, infected the year before by pelrine and
flaclierie, Pasteur reproduced flaclierie, and not pebrine.
Still more readily did he produce the first of these
maladies, when he gave, as food, leaves polluted by
the contents of the intestinal canal of worms which
had died of the disease. As in the case of pelrine,
the excreta of the worms attacked by flaclierie, de-
filing the leaves, carry .the mischief to the healthy
worms, or add to the dangerous fermentation in the
intestines of those which are already in part attacked.

To preserve silkworms from accidental flaclierie,
hygienic precautions are sufficient. As regards here-
ditary flaclierie, or, to speak more correctly, that which
develops itself easily on any diminution of vigour in
the eggs and in the embryo, Pasteur again found a
remedy by having recourse to the microscope. By
means of the microscope it is possible to obtain in-
formation as to the health of the worms, the chry-

THE SILKWORM-DISEASE. 159

salides, and the moths destined to produce the eggs.
Every attention should be directed to the complete
exclusion of ferments from the intestinal canal of the
worms, and from the stomach-pouch of the chrysalides —
a little pouch to which the intestinal canal of the worm
is reduced, with its contents more or less transformed.
But if there is not time to make this examination for
parasitic ferments with the microscope, a simple in-
spection of the worms in their last stage will suffice.
Pasteur laid great stress upon the observation of the
worms when they climbed on to the heather.

' If I were a cultivator of silkworms,' he wrote in
his beautiful work on the diseases of silkworms, 'I
would never hatch an egg produced from worms that
I had not observed many times during the last days
of their life, so as to make sure of their vigour at the
moment when they spin their silk. If you use eggs
produced by moths the worms of which have mounted
the heather with agility, have shown no signs of
flaclierie between the fourth moulting and mounting
time, and do not contain the least corpuscle of pebrine,
then you will succeed in all your cultivations.'

III.

We have now arrived at the end of this long in-
vestigation. All the obscurity which enveloped the
origin of the diseases of silkworms had now been dis-

160 LOUIS PASTEUK.

pelled. Pasteur had arrived at such accurate know-
ledge both of the causes of the evil and their different
manifestations, that he was able to produce at will
either pebrine or flaclierie. He could so regulate the
intensity of the disease as to cause it to appear on a
given day, almost ,at a given hour. He had now to
carry into practice the results of his laboratory
labours.

Since the beginning of the plague, and after some
doubts which were soon dispelled, it was clearly seen
that all the mischief was to be attributed to the bad
condition of the eggs. The remedy of distant explora-
tions for procuring non-infected eggs was both insuffi-
cient and precarious. It simply amounted to going,
very far to seek, and paying very dear, for seed
which could not be relied on with certainty. The
prosperity of the silkworm culture could only be
secured by measures capable of restoring to the native
eggs their pristine qualities.

The results obtained by Pasteur were sufficient to
solve this problem. The struggle against flaclierie
was easy, but there remained the struggle against
pebrine. To triumph over this disease, which was so
threatening, Pasteur devised a series of observations
as simple as they were ingenious.

Here is a crop which has perfectly succeeded. The
moultings, and the climbing upon the heather, are all
that could be desired. The cocoons are finished, and the

THE SILKWORM-DISEASE. 161

appearance of the moths alone is waited for. They
arrive, and they pair. Then begins the work of the
cultivator, who is careful about the production of his
eggs. He separates the couples at the end of the day ;
laying each female moth by itself on a little linen
cloth suspended horizontally. The females lay their
eggs. After the laying, he takes each female in turn
and secures her by a pin passed through the wings to
a folded corner of the little cloth, where are grouped
some hundreds of eggs which she has laid. The male
moth also might be pinned in another corner of
the cloth, but the examination of the male is useless,
as it has been found that he does not communicate
the pebrine. The female moth, after having been
desiccated by free contact with the air, is examined at
leisure, it may be even in the autumn or winter. No-
thing is easier than to ascertain whether there are any
corpuscles in its dead body. The moth is crushed in a
mortar and mixed with a little water, and then a drop
of the mixture is examined by the microscope. If
corpuscles be found, the bit of cloth corresponding to
the examined moth is known, and it is burnt with all
the eggs it contains.

This method of procuring pure eggs is, in fact, only
the rational development of the first inductions which
Pasteur had submitted to the Agricultural Committee
of Alais in June 1865. At that time he hardly ven-
tured to hope that he should be able to find the means

162 LOUIS PASTEUR.

of preparing more than very small quantities of
healthy eggs for his experiments; but events were
so ordered that the starting-point, which seemed to
be purely scientific, unfolded a method susceptible
of a widespread practical application. This process
of procuring sound eggs is now universally adopted.
In the Basses-Alpes, in Ardeche, in Gard, in the
Drome, and in other countries, may be met with
everywhere, at the time of the cultivation, workshops
where hundreds of women and young girls are occu-
pied, with a remarkable division of labour and under
the strictest supervision of skilful overseers, in pound-
ing the moths, in examining them microscopically,
and in sorting and classifying the little cloths upon
which the eggs are deposited.

But if Pasteur had brought back wealth to ruined
countries, if he had returned to Paris happy in the
victory he had gained, he had also undergone such
fatigues, and had so overstrained himself in the use
of the microscope while absorbed in his daily and
varied experiments, that in October 1868 he was
struck with paralysis of one side. Seeing, as he
thought, death approaching, he dictated to his wife a
last note on the studies which he had so much at
heart. This note was communicated to the Academy
of Sciences eight days after this terrible trial.

A soul like his, possessing so great a mastery over

THE SILKWORM-DISEASE. 163

the body, ended by triumphing over the affliction.
Paralysed on the left side, Pasteur never recovered the
use of his limbs. To this day, sixteen years after the
attack, he limps like a wounded man. But what
stages had this wounded man yet to travel over, what
triumphs were yet in store for him !

M 2

164 LOUIS PASTEUK,

DECISIVE EXPERIMENTS.

AFTER having dictated this scientific note, which he
thought would have been his last, his courage forsook
him for a time. ' I regret to die,' he said to his
friend, Sainte- Claire Deville, who had hastened to his
bedside ; ' I should have wished to render more service
to my country.' His life was spared, but for several
months Pasteur remained entirely paralysed, incapable
of the slightest movement. Smitten thus in his full
strength at the age of forty-five, he took a sad review
of his own state. Even at the height of his attack
his mind had always retained its clearness. He had
pointed out to the doctor without any faltering of
voice the progressive symptoms of the paralysis. Then
reproaching himself for having added to the grief of
his wife by thus dwelling on the details of his illness,
he never allowed another word to escape him about
his infirm condition. Sometimes, even when he
heard his two assistants, M. Gernez and M. Duclaux,
whose devotion to him during those sad days could
only be compared to that of his wife, talking to him of

DECISIVE EXPERIMENTS. 165

future labours, he entered into these thoughts and
appeared to add faith to their hopes. He finished by
sharing them.

In January 1869, although it was still impossible
for him to drag himself about his room, he was so
much excited by the contradictions that his system of
culture had aroused that he wished to start again for
Alais. 'Aided by the method of artificial cultivation,'
he remarked, ' we shall soon annihilate these latest
oppositions. There is here both a scientific principle
and an element of national wealth.'

His wish could not be opposed, but a terrible and
anxious journey it was ! At some leagues from Alais,
at a place called Saint Hippolyte-du-Fort, where the
earliest experiments were made, Pasteur stopped. He
installed himself — we might rather say he encamped
—with his family and his assistants, in a more than
humble lodging, one of those miserable, cold, paved
houses of the rural districts. Seated in his arm-
chair, Pasteur directed the experiments, and verified
the observations which he had made the year before.
Each of his predictions as to the destiny of the dif-
ferent groups of worms was fulfilled to the smallest
detail. In the following spring he left for Alais,
where he followed in all their phases, from the egg
up to the cocoon, the cultivations there undertaken,
and he had the happiness of proving once more the
•certainty of his method.

166 LOUIS PASTEUK.

But opposition still continued. The French
Government, shaken by the violence and tenacity of
the opponents, hesitated to decide upon this process
of culture. The Emperor interposed ; he instructed
Marshal Vaillant to propose to Pasteur to go into
Austria to the Villa Vicentina, which belonged to the
Prince Imperial. For ten years the silk harvest at
this place had not sufficed to pay the cost of eggs.
Pasteur accepted with joy the prospect of a great
decisive experiment. He traversed France and Italy,
reclining in a railway carriage or in an arm-chair,
and at last arrived at the Imperial villa near Trieste.
Pasteur succeeded in a marvellous manner. The
sale of the cocoons gave to the villa a nett profit of
twenty- six million francs. The Emperor, impressed
with the practical value of the system, nominated
Pasteur a Senator, in the month of July 1870. But
this nomination, like so many other things, was swept
away before it had time to appear in the ' Journal
Officiel.' Pasteur, however, cared little for the title
of Senator. He returned to France on the eve of the
declaration of war.

A patriot to the heart's core, he learned with
poignant grief the news of his country's disasters. The
bulletins of defeat, which succeeded each other with
mournful monotony, threw him into deep despair. For
the first time in his life he had not the strength to
work. He lived at his little house in Arbois as one

DECISIVE EXPERIMENTS. 167

completely vanquished. Those who went into his
room found him often bathed in tears. On January
18, 1871, he wrote, to the Dean of the Academy
of Medicine at the University of Bonn, a letter
in which all his grief and all his pride as a
Frenchman were displayed, requesting him to with-
draw the diploma of German doctor which the
Faculty of Medicine of the University had conferred
upon him in 1868. Whilst he wrote this letter,
which was a cry of patriotism, his son, enrolled as a
volunteer, though hardly eighteen years of age, was
gallantly doing his duty in the Army of the East.

168 LOUIS PASTEUR.

STUDIES ON BEER.

THE war was over. Little by little the life of the
country was resumed, and with returning hope the
desire and necessity for renewed work. After two
years of infirmity, Pasteur at length began to feel
the recovery of health. It was like a slow and gentle
renewal of all things. He wished to return as soon
as possible to his laboratory in Paris to put into exe-
cution projects of experiments which had long been
working in his brain. At the moment when he was
preparing to start, the rebellion of the Commune broke
out. M. Duclaux, who had become Professor of the
Faculty of Sciences in Clermont-Ferrand, offered the
use of his laboratory to his old master. Pasteur ac-
cepted it. Eager to commence an investigation which
would bring him again to the study of fermentation,
he attacked the diseases of beer. But it was not only
for the purpose of creating a new link between these
researches and his former ones that he occupied him-
self with this subject, he was also influenced by a
somewhat patriotic idea. He dreamt of success in an

STUDIES ON BEEK. 169

industry in which Germany is superior to France. He
hoped by means of scientific principles, by which com-
merce would largely profit, to succeed in making for
French beer a reputation equal, if not superior, to
that of Germany.

Beer is much more liable to contract diseases than
wine. It may be said that while old wine is often to be
found, there is no such thing as old beer. It is con-
sumed as fast as it is made. Less acid and less
alcoholic than wine, beer is more laden with gummy
and saccharine matters, which expose it to rapid
changes. Thus the trade in this beverage is constantly
struggling with the difficulties of its preservation.

The manufacture of beer is simple. It is extracted
from germinated barley, or malt, an infusion of which
is made and gradually heated to the boiling point.
It is then flavoured by hops. When the infusion of
malt and hops, which is called ' wort,' is completed,
it is subjected to a cooling process, and drawn off into
tuns and barrels. It is then that alcoholic fermenta-
tion sets in. The cooling ought to be performed
rapidly. While the wort is at a high temperature
there is nothing to fear, it remains sound ; but under
70° Centigrade, and particularly between 25° and 35°,
it is easily attacked by injurious ferments — acetic,
lactic, or butyric. After the wort is cooled, a little
of the yeast proceeding from a former fermentation

170 LOUIS PASTEUK.

is added to it, in order that the whole mass of the
wort should be invaded as soon as possible after its
cooling by the alcoholic ferment alone — the only one,
properly speaking, which can produce beer. If this
wort were treated in the same way as the must of
the grape, if it were abandoned to fermentation with-
out yeast — to so-called spontaneous fermentation —
this would hardly ever be purely alcoholic, as in the
must of grapes, which is protected by its acidity.
Most frequently, instead of beer, an acid or putrid
liquid would be obtained. Divers fermentations
would simultaneously take place in it. When the
wort has fermented and the beer is made, there is
still the fear of its rapid deterioration, which necessi-
tates its being quickly consumed. This condition
is sometimes disastrous to those employed in the
beer trade ; and the improvements in the manufac-
ture of beer which have been made during the last
forty years have all had for their object the removal of
this necessity for the daily production, so to speak, of
an article of which the consumption is liable to con-
stant variations.

Formerly only one kind of beer was known, the
beer of high fermentation. The wort, after having
undergone cooling in the troughs, is collected in a
large open vat at a temperature of 20°, and yeast is
added to it. When the fermentation begins to show
itself on the surface of the liquid, by the formation of

STUDIES ON BEER. 171

a light white froth, the wort is transferred to a
series of small barrels, which are placed in cellars
or store-rooms, kept at a temperature of from 18°
to 20° Centigrade. The activity of the fermentation
soon causes a foam to rise, which becomes more
and more thick and viscous. This is owing to the
abundance of yeast which it contains. This yeast,
collected in a large trough placed under the casks,
is gathered up for future operations. The fermenta-
tion lasts for three or four days, then the beer is
made and has become clear; the bungs are fixed
in the barrels, and they are sent direct to the retail
dealer or to the consumer. During the transit, a
certain quantity of yeast, fallen to the bottom of the
casks, thickens the beer, but a few days of repose suffice
to make it again clear and fit to drink, or to be bottled.

This system of ' high ' fermentation (so called be-
cause it begins at a temperature of 18° to 20°, and is
raised one or two degrees higher by the act of fer-
mentation itself) is very commonly practised in the
north of France, and to a greater extent in the
breweries of England. Ale, pale ale, bitter beer, are
all beers from high fermentation.

The ' low ' fermentation, which is almost exclusively
employed in Germany, and which is spreading more
and more in France, consists in a slow fermentation,
at low temperature, during which the yeast settles
at the bottom of the tubs and casks. The wort,

172 LOUIS PASTEUK.

after it has been cooled, is passed into open wooden
tuns, and the working of the yeast takes place at a tem-
perature of about 6° Centigrade. This temperature is
maintained by means of floats, in the form of cones
or cylinders, thrown into the fermenting tuns and
kept filled with ice. The fermentation lasts for ten,
fifteen, and even twenty days. When the beer is
drawn off, the yeast is collected from the bottom of the
fermenting tuns. This kind of beer, which is some-
times called German beer, sometimes Strasburg beer,
is generally much more esteemed than the other, but
it requires certain expensive, or at least inconvenient,
conditions. There must be ice-caves, where the tem-
perature is maintained all the year round at a few
degrees only above zero. This makes it necessary to
have enormous piles of ice. It has been calculated that
for one single hectolitre of good beer, from the begin-
ning of the cooling of the wort until the time when it
is fit for sale, 100 kilogrammes of ice are required.
The ' low ' beer, called also biere de garde, beer for keep-
ing, is principally manufactured in winter, and is
preserved in ice-caves until the summer.

It is not only the taste of the consumers which
has favoured the manufacture of beer of low fermen-
tation everywhere except in England ; it is also the
advantage this beer possesses in being much less liable
to deterioration than the other. By employing ice, the
brewer may manufacture in winter, or in the beginning

STUDIES ON BEEK. 173

of spring, and thus place himself in a position to meet
the demands of consumption without fear of seeing
his beer attacked by disease.

All the diseases of beer, as Pasteur has shown,
are caused exclusively by the development of little
microscopic fungi, or organised ferments, the germs
of which are brought by the dust constantly floating
in the air, or which gets mixed with the original sub-
stances used in the manufacture. 'By the expression
diseases of wort and of beer, I mean,' said Pasteur,
' those serious alterations which affect the quality of
these liquids so as to render them disagreeable to the
taste, especially when they have been kept for some
time, and which cause the beer to be described as
sharp, sourish, turned, ropy, putrid.' The wort of beer,
after it has been raised to the boiling heat, may, as
Pasteur's experiments testify, be preserved indefinitely,
even in the highest atmospheric temperatures, when
in contact with air free from the germs of the lower
microscopic organisms. The must, leavened by the
addition of pure yeast, kept free from foreign organ-
isms, contains nothing but the alcoholic ferment, and
undergoes no other changes than those due to the
action of the oxygen, which does not give rise to
acidity, putridity, or bitterness. Since the causes of
deterioration are the same in beer as in wine, would
it not appear as if the action of heat must be the best

174 LOUIS PASTEUK.

preservative ? But beer is a drink necessarily charged
with carbonic acid, and the application of heat to con-
siderable masses of the liquid would expel this gas.
It would be a very complicated business to attempt to
preserve this gas, or to introduce it afresh after it had
been expelled. This difficulty does not arise when the
beer is bottled. At a temperature of 50° to 55°,
the process of heating not only cannot take away
from the beer all its carbonic acid, but it does not
prevent the secondary fermentation from taking place
to a certain extent, and this allows of the beer being
heated immediately after it is put into bottles. This
heating of the beer is practised on a large scale in
Europe and in America. In honour of Pasteur the
process is called Pasteurisation, and the beer Pas-
teurised beer.

But Pasteur was not content with simply destroying
the ferments of these diseases, he wished above all to
prevent their introduction. At the moment when
the wort is raised to the boiling-point, when the
germs of disease are destroyed by the heat, if the
cooling of the wort is effected in contact with both
air and yeast free from exterior germs, the beer may
be made under conditions of exceptional purity. Some
brewers, taking for their basis Pasteur's principles, con-
structed an apparatus which enabled them to protect
the wort while it was cooling from the organisms of
the air, and to ferment this wort with a leaven as

STUDIES ON BEER. 175

pure as possible. At the Exhibition of Amsterdam
there might be seen bottles half full, containing a per-
fectly clear beer, which had been tapped from the
time of opening of the Exhibition. This was French
beer, manufactured according to Pasteur's principles,
by a great brewer of Marseilles, M. Velten. The
happy effect of these studies is universally recognised.
At Copenhagen, M. Jacobsen has had a bust of Pasteur,
by Paul Dubois, placed in the salle d'honneur of his
celebrated laboratory.

In terminating his Studies on Beer, Pasteur re-
called to mind the principles which for twenty years
had directed his labours, the resources and applica-
tions of which appeared to him unlimited. ' The
etiology of contagious diseases,' he wrote with a scien-
tific certainty of conviction, ' is on the eve of having
unexpected light shed upon it.'

176 LOUIS PASTEUE.

VIRULENT DISEASES.

SPLENIC FEVER (CHAEBON) — SEPTICAEMIA.

' HE that thoroughly understands the nature of fer-
ments and fermentations,' said the physicist Eobert
Boyle, ' shall probably be much better able than he
that ignores them, to give a fair account of divers
phenomena of certain diseases (as well fevers as
others), which will perhaps be never properly under-
stood without an insight into the doctrine of fermen-
tations.'

At all times, medical theories, more particularly
those which concern the etiology of virulent diseases,
have had to encounter the opposition of explanations
invented to account for the phenomena of fermenta-
tion. When Pasteur in 1856 began his labours on
these subjects, the ideas of Liebig were everywhere
revived. Like the ferments, so the viruses and
processes of disease were considered as the results of
atomic motions proper to substances in course of
molecular change, and able to communicate themselves
to the diverse constituents of the living body.

The researches of Pasteur on the part played by

VIEULENT DISEASES. 177

microscopic organisms in fermentation, changed the
course of these ideas. The ancient medical theory of
parasites and living contagia was revived. A German
Professor, Dr. Traube, in 1864, put forward, in one of
his clinical lectures, a new doctrine of the ammoniacal
fermentation of urine.

' For a long period,' he said, ' the mucus of the
bladder was regarded as the agent of the alkaline
decomposition of urine. It was supposed that, in
consequence of the distension produced by the reten-
tion of the liquid, the irritated bladder produced a
larger quantity of mucus, and this mucus was re-
garded as the ferment which brought about the
decomposition of urea, by an innate chemical
force. This opinion (which was that of Liebig) can-
not hold its ground in presence of the researches of
Pasteur. This investigator has demonstrated, in the
most decisive manner, that alkaline fermentation, like
alcoholic and acetic fermentation, is produced by
living organisms, the pre-existence of which in the
liquid is the sine qua non of the process.' And Dr.
Traube, citing some facts which confirmed the doc-
trine of Pasteur, concluded thus : ' Notwithstanding
the long retention of the urine, its alkaline fermenta-
tion is not produced by an increased secretion of
mucus or of pus ; it only begins to develop from
the moment when the germs of vibrios find access
to the bladder from without,

N

178 LOUIS PASTEUK.

The opposite doctrines of Liebig and Pasteur
are here brought into clear juxtaposition ; and thus
was their mutual and reciprocal influence established
in dealing with the etiology of one of the most serious
diseases of the bladder. So far back as 1862, Pasteur,
in his memoir on spontaneous generation, had an-
nounced, contrary to all the notions then held, that
whenever urine becomes ammoniacal, a little micro-
scopic fungus is the cause of this alteration. Later
on he established that in affections of the bladder
ammoniacal urine was never found without the pre-
sence of this fungus ; and in order to show how in
these studies therapeutic application often runs hand
in hand with scientific discovery, Pasteur, having
proved, with his assistant, M. Joubert, that boracic
acid is antagonistic to the development of the am-
moniacal ferment, advised Dr. Guyon, Clinical Pro-
fessor of Urinary Diseases in the Faculty of Paris, to
combat the dangerous ammoniacal fermentation by
injection of boracic acid into the bladder. The
celebrated surgeon hastened to follow this advice, and
with the most happy results. While attributing to
Pasteur the honour of this discovery, M. Guyon, in
one of his lectures, said : —

' Boracic acid has this immense advantage, that it
can be applied in large doses — 3 to 4 per cent. — with-
out causing the slightest pain. It has therefore
become, in our practice, the agent continually and

VIKULENT DISEASES. 179

successfully used for injections. I also have recourse
to a solution of boracic acid to produce large evacua-
tions after the operation of breaking up stones in the
bladder (lithotrity). I never omit to use this anti-
septic agent in operations where breaking up is re-
quired, and I never wash the bladders of lithotritised
patients with any other substance. I have also had
good results from copiously washing the bladders
and the wounds of patients on whom lithotomy has
been performed with boracic acid. I always finish
the operation by prolonged irrigations with a solution
of from 3 to 4 per cent.'

It was not only into France and Germany that
Pasteur's ideas penetrated ; in England, surgery bor-
rowed from Pasteur's researches important thera-
peutic applications. In 1865 Dr. Lister began in
Edinburgh the brilliant series of his triumphs in
surgery by the application of his antiseptic method,
now universally adopted. In the month of February
1874 in a letter which does honour to the sincerity
and modesty of the great English surgeon, he wrote
to Pasteur as follows : —

' It gives me pleasure to think that you will read
with some interest what I have written about an or-
ganism which you were the first to study in your
memoir on lactic fermentation. I do not know
whether you read the ' British Medical Journal ; ' if
so, you will from time to time have seen accounts of

N 2

180 LOUIS PASTEUR.

the antiseptic system which for the last nine years I
have been trying to bring to perfection. Allow me to
take this opportunity of sending you my most cordial
thanks, for having, by your brilliant researches, de-
monstrated to me the truth jajMbhe germtheory of
putrefaction, thus giving me the only principle which
could lead to a happy end the antiseptic system.'

Pasteur followed with lively interest the movement
of thought and the successful applications to which
his labours had given rise. It was a realisation of
the hopes he had ventured to entertain. Already,
in 1860, he expressed the wish that he might be able
to carry his researches far enough to prepare the
way for a profound study of the origin of diseases.
And, as he gradually advanced in the discovery
of living ferments, he hoped more and more to
arrive at the knowledge of the causes of contagious
diseases.

Nevertheless, he hesitated long before definitely
engaging himself in this direction. ' I am neither
doctor nor surgeon,' he used to repeat with modest self-
distrust. But the moment came when, notwithstand-
ing all his scruples, he could no longer be content
himself to play the part of a simple spectator of the
labours started by his studies on fermentation, on
spontaneous generation, and on the diseases of wines
and beer. The hopes to which his methods gave rise,
the eulogies of which they were the object, obliged

VIRULENT DISEASES. 181

him to go forward. In February 1876 Tyndall wrote
to him thus : —

' In taking up your researches relating to infusorial
organisms, I have had occasion to refresh my memory
of your labours ; they have revived in me all the ad-
miration which I felt on first reading them. It is my
intention to follow up these researches until I shall
have dissipated every doubt that has been raised as to
the unassailable exactitude of your conclusions.

' For the first time in the history of science we are
able to entertain the sure and certain hope that, in
relation to epidemic diseases, medicine will soon be
delivered from empiricism, and placed upon a real
scientific basis. When this great day shall come,
humanity will recognise that it is to you the greatest
part of its gratitude is due.'

Pasteur approached the study of viruses by seeking
to penetrate into all the causes of the terrible malady
called splenic fever (charbon, Germ. Milzbrand). Each
year this disease decimates the flocks not only in France
but in Spain, in Italy, in Eussia, where it is called the
Siberian plague, and in Egypt, where it is supposed to
date back to the ten plagues of Moses. Hungary and
Brazil pay it a formidable yearly tribute ; and to come
back to France, the losses have amounted in certain
years to from fifteen to twenty millions of francs.
For centuries the cause of this pest has eluded all re-
.search ; and further, as the malady did not always

182 LOUIS PASTEUR.

exhibit the same symptoms, but varied according to
the kind of animal that was smitten by it, the
disease was supposed to vary with the species that
' was attacked by it. The splenic fever of the horse
was, distinct from that of the cow ; the splenic fever of
horse and cow were again different from that of the
sheep. In the latter, splenic fever was called sany-de-
rate ; in the cow, it was maladie du sang ; in the horse,
splenic fever ; in man, malignant pustule.

It was not until 1850 that trustworthy data were
first collected regarding the nature of the malady, its
identity with and difference from other maladies.
From 1849 to 1852 a commission of the Medical
Association of Eure-et-Loir made a great number of
inoculations, applied other tests, and proved that the
splenic fever of the sheep is communicable to other
sheep, to the horse, to the cow, and to the rabbit ;
that the splenic fever of the horse is communicable to
the horse and to the sheep ; that the splenic fever of
the cow is communicable to the sheep, to the horse,
and to the rabbit. As for the malignant pustule
in man, no doubt remained that it must arise from
the same cause as splenic fever in animals. What
class of men is it that the malignant pustule most
frequently attacks ? Shepherds, cowherds, cattle
breeders, farm servants, dealers in hides, tanners,
wool cleaners, knackers, butchers— all who derive
their living from domestic animals. In handling con-

VIEULENT DISEASES. 183

taminated subjects the slightest excoriation or scratch
of the skin is sufficient to allow the virus to enter.
When others besides the class that we have named
become infected, it is because they live in the neigh-
bourhood of herds smitten with splenic fever. There
are also certain flies which transport the virus. Sup-
pose one of these flies to have sucked the blood of an
animal which has died of splenic fever, a person
stung by that fly is forthwith inoculated with the
virus.

At the very time (1850) when these first experi-
ments were being made by the Medical Association of
the Eure-et-Loir, Dr. Eayer, giving an account in the
' Bulletin de la Societe de Biologie de Paris ' of the
researches he had made, with his colleague, Dr.
Davaine, on the contagion of splenic fever, wrote : —
'In the blood are found little thread-like bodies
about twice the length of a blood corpuscle. These
little bodies exhibit no spontaneous motion.'

This is the date of the first observation on the
presence of little parasitic bodies in splenic fever, but,
strange to say, no attention was paid to these minute
filaments. Kayer and Davaine also paid no atten-
tion to them. This indifference lasted for thirteen
years ; it would have lasted longer still, if the parasitic
origin of communicable diseases had not been brought
before the mind by each new publication of Pasteur's.
From 1857 to 1860 it will be remembered that he had

184 LOUIS PASTEUK.

demonstrated lactic fermentation, like alcoholic fer-
mentation, to be the work of a living ferment ; in
1861 he had discovered that the agent of butyric
fermentation consisted of little moving thread-like
bodies, of dimensions similar to those of the filaments
discovered by Davaine and Bayer in the blood of
splenic fever patients; in 1861 he had announced
that no ammoniacal urine existed without the pre-
sence of a microscopic organism ; in 1863 he had
established that the bodies of animals in full health
are sealed against the introduction of the germs of
microscopic organisms; that blood drawn with suf-
ficient precaution from the veins and the arteries,
and urine taken direct from the bladder, could be
exposed to the contact of pure air without putre-
faction, and without the appearance of living thread-
like organisms of any kind whatever, mobile or
immobile. It was all these facts which in 1863
brought back the attention of Davaine, as he himself
has acknowledged, to the observation which he had
made in 1850.

' M. Pasteur,' said M. Davaine in a communication
made to the Academy of Sciences, ' published some
time ago a remarkable memoir on butyric fermenta-
tion, which consists of little cylindrical rods, possess-
ing all the characteristics of vibrios or of bacteria.
The thread-like corpuscles which in 1850 I saw in the
blood of sheep attacked with sang-de-rate, having

VIKULENT DISEASES. 185

a, great analogy with these vibrios, I was led to
examine whether filiform corpuscles, analogous to or of
the same kind as those which determined the butyric
fermentation, would not, if introduced into the blood
of an animal, equally act the part of a ferment.
Thus would be easily explained the alteration, and the
rapid infection of the mass of the blood, in an animal
which had received accidentally or experimentally into
its veins a certain number of these bacteria — that is to
say, of this ferment.'

But two summers passed before M. Davaine was
able to procure a sheep affected with the sang -de-rate.
It was only in 1863 that he first recognised the
constant presence of a parasite, in the blood of sheep
and rabbits which had died from successive inocula-
tions with blood taken after death or in the last hours
of life. He further proved that the inoculated animal,
in the blood of which no parasites were as yet visible
with the microscope, had every appearance of health,
and that in these conditions the blood could not com-
municate splenic fever.

'In the present state of science,' Davaine con-
cluded, ' no one would think of going beyond these
corpuscles to seek for the agent of the contagion. This
agent is visible, palpable ; it is an organised being,
endowed with life, which is developed and propagated
in the same manner as other living beings. By its
presence, and its rapid multiplication in the blood, it

186 LOUIS PASTEUK.

without doubt produces in the constitution of this liquid,
after the manner of ferments, modifications which
speedily destroy the infected animal.' ' For a long
time,' he repeated, * physicians and naturalists have
admitted theoretically that contagious diseases, serious
epidemic fevers, the plague, &c., are caused by invisible
animalculse, or by ferments, but I do not know that
these views have ever been confirmed by any positive
observations.'

A few months after the publication of the results
obtained by Davaine, two professors of Val-de-Grace,
MM. Jaillard and Leplat, sought to refute the pre-
ceding conclusions. After having inoculated rab-
bits and dogs with various putrefying liquids filled
with vibrios, they could not cause the death of these
animals. To bring about this result it was necessary
to introduce into the blood of these dogs and rabbits
several cubic centimeters of very putrid liquid. Again
in this case, which only added another example to the
experiments of Gaspard and Magendie upon the action
of putrid liquids, they failed to generate any virulence
in the blood. Davaine had no difficulty in showing
that MM. Jaillard and Leplat's experiments were made
under conditions totally different from his ; that he,
Davaine, had not made use of the vibrios or bacteria
of unselected infusions, but of bacteria which had
been found in the blood of sheep which had died
from sang -de-rate.

VIRULENT DISEASES. 187

Jaillard and Leplat returned to the charge, and
this time with entirely new and unexpected experi-
ments. They inoculated some rabbits, as Davaine
desired, with the blood of a cow which had died of
splenic fever. The rabbits died rapidly, but without
showing before or after their death the least trace of
bacteria. Other rabbits, inoculated with the blood of
the first, perished in the same manner, but it was
still impossible to discover any parasite in their blood.
MM. Jaillard and Leplat offered Davaine some drops of
this blood. Davaine, taking up the experiments of
his opponents, confirmed the exactitude of the facts
they had announced, but concluded by saying that
these two professors had not employed true splenic
fever blood, but the blood of a new disease, unknown
up to that time, which Davaine proposed to call the
cow disease.

* The blood which we used,' replied MM. Jaillard
and Leplat, ' was furnished to us by the director of the
knacker's establishment of Sours, near Chartres, and
this director is undeniably competent as to the know-
ledge of splenic fever.'

Full of sincerity and conviction, MM. Jaillard
and Leplat recommenced their experiments, using
this time the blood of a sheep which had died of splenic
fever, and which M. Boutet, the most experienced
veterinary surgeon of the town of Chartres, had pro-
cured for them. Their results were the same as those

188 LOUIS PASTEUR.

obtained with the blood of the cow. Notwithstand-
ing the replies of Davaine, which, however, added
nothing to the facts already adduced on one side or the
other, it was difficult to pronounce decidedly in such
a debate. Unprejudiced minds received from these
important discussions the impression that Jaillard and
Leplat, in producing facts the exactitude of which
were admitted by Dr. Davaine himself, had given a
blow to the assertions of the latter, and that the
subject required, in every case, new experimental
studies.

In 1876, a German physician, Dr. Koch, took
up the question. He confirmed the opinion of
Davaine, but without in the least producing convic-
tion, since he threw no light upon the facts adduced
by MM. Jaillard and Leplat, of which, indeed,
he did not even deign to speak. At the very same
moment when the memoir of Koch appeared in
Germany, the eminent physician Paul Bert came
forward to corroborate the opinion of Jaillard and
Leplat.

* I can,' said M. Paul Bert, ' destroy the bacteria in
a drop of blood by compressed oxygen, inoculate with
what remains, and reproduce the disease and death
without any appearance of bacteria. Therefore, the
bacteria are neither the cause nor the necessary effect
of the disease of splenic fever. It is due to a virus.'

This was indeed the opinion of Jaillard and Leplat.

VIRULENT DISEASES. 189

Pasteur, in obedience to the necessity he felt to get at
the fundamental truth of things, and also in his eager
desire to discover some decisive proofs as to the
etiology of this terrible disease, resolved in his turn
to attack the subject.

Dr. Koch had stated in his memoir that the little
filiform bodies, seen for the first time by Davaine in
1850, had two modes of reproduction — one by fission,
which Davaine had observed, and another by bright
corpuscles or spores. The existence of this latter
mode of reproduction Pasteur had already discovered
in 1865, reasserted and illustrated in 1870, as being
common to the filaments of the butyric ferment, and
to all the ferments of putrefaction. Was Dr. Koch
ignorant of this important fact, or did he prefer by
keeping silence to reserve to himself the advantage of
apparent priority ?

In order to solve the first difficulty which pre-
sented itself to his mind — that is to say, the question
as to whether splenic fever was to be attributed to a
substance, solid or liquid, associated or not associated
with the filaments discovered by Davaine, or whether it
depended exclusively upon the presence and the life of
these filaments — Pasteur had recourse to the methods
which for twenty years had served him as guides
in his studies on the organisms of fermentation.
These methods, delicate as they are, are very simple.
.When he wished, for example, to demonstrate that the

190 LOUIS PASTEUR.

microbe-ferment of the butyric fermentation was the
very agent of decomposition, he prepared an artificial
liquid formed of phosphates of potash, of magnesia,
and of sulphate of ammonia, added to the solution of
the fermentable matter, and in this medium he caused
the microbe- ferments to be sown in a pure state.
The microbe multiplied, and provoked fermentation.
From this liquid he could pass to a second or third
fermentable liquid composed in the same manner,
and so on in succession. The butyric fermentation
appeared successively in each. Since the year 1857
this method was supreme. In this particular research
on the disease of splenic fever Pasteur proposed
to isolate the microbe of the infected blood, to cul-
tivate it in a state of purity in artificial liquids, and
then to come back to the examination of its action
on animals. But as, since his attack of paralysis
in 1868, Pasteur had not recovered the use of his
left hand, and consequently found it impossible to
carry on a long series of experiments alone, he was
obliged to seek for a courageous and devoted assistant.
He found one in a former pupil of his at the Ecole
Normale, M. Joubert, now Professor of Physics at the
College Kollin. If M. Joubert incurred the danger of
these experiments on splenic fever, he also shared
with Pasteur, in the Comptes-rendus of the Academy of
Sciences, the honour of the researches and the triumph
of the discoveries.

VIRULENT DISEASES. 191

On April 30, 1877, Pasteur read to the Academy
of Sciences, in his own name and in that of his
fellow-worker, a note in which he demonstrated, this
time in a completely unanswerable manner, that the
bacilli called bacteria, bacterides, filaments, rods,
in a word the bacilli discovered by Davaine and
Eayer in 1850, constituted the only agent of the
malady.

A little drop of splenic fever blood, sown in
urine or in the water of yeast, previously sterilised—
that is to say, rendered wiputrescible by contact with
air free from all suspended germs — produces in a few
hours myriads of bacilli or of bacteria. A little drop
of this first cultivation sown iri a second flask contain-
ing the same liquid as the first and prepared with the
same precautions as to sterility and purity, shows it-
self no less fertile. Finally, after ten or twenty
similar cultures the parasite is evidently freed from the
substances which the initial drop of blood might carry
with it ; yet, if a very small quantity of the last cul-
ture is injected under the skin of a rabbit or a sheep,
it kills them in two or three days at most, with all the
clinical symptoms of natural splenic fever.

It might be objected that the parasite was associ-
ated in the cultivating liquid with some dissolved sub-
stance that it had produced during its life and which
acted as a poison. Pasteur accordingly transported
some cultivating tubes into the cellars of the Observa-

192 LOUIS PASTEUR.

tory, where a temperature absolutely constant reigned,
a circumstance which permits of the deposit of all
the parasitic filaments at the bottom of the tubes.
Inoculating afterwards both with the clear upper
liquid and with the deposit at the bottom, he found
that the latter alone produced disease and death. It
is, then, the bacteria which cause splenic fever. The
proof was given and no further doubt remained.

I.

Yes, splenic fever is no doubt produced by bacteria
just as itch is produced by acaries and trichinosis
by trichinae. The only difference is that the para-
site of splenic fever can only be seen by means of a
rather powerful microscope. Here, then, is a disease
in the highest degree virulent, due in its first cause to
the infinitely little. Pasteur laid hold of and isolated
this terrible virus. It was in a microscopic parasite,
and in it alone, that the virulence of splenic fever re-
sided. A great scientific fact had been gained. A
virus might consist not of amorphous matter, but of
microscopic beings. The virulence was due to the
life.

Liebig, and all the chemists and doctors who had
accepted and maintained his doctrine, totally repudi-
ated all vital action in fermentation as well as in con-
tagious and infectious diseases. Dominated by their

VIRULENT DISEASES. 198

hypotheses, they allowed themselves to be deceived by
false assimilations to facts of a purely chemical kind,
which appeared to them to be connected with the phe-
nomena of fermentation and virulence.

Liebig wrote, ' By the contact of the virus of small-
pox the blood undergoes an alteration, in consequence
of which its elements reproduce the virus, and this
metamorphosis is not arrested until after the complete
transformation of all the globules capable of decompo-
sition.'

This vague theory of viruses was forced to give
way before the multiplied experiments of Pasteur.
But before occupying himself with further discoveries,
although it had been irrefutably proved that the
microscopic parasite was the true contagium, it was
necessary to throw light upon the facts, mainly accu-
rate, which had been announced by Jaillard and
Leplat, and to bring them into harmony with the facts,
not less certain, which had been advanced by Davaine.
The rabbits which Jaillard and Leplat had inoculated
with a drop of the blood of a cow or sheep stricken
with splenic fever, died rapidly, and the blood of these
rabbits was shown to be also virulent. It was suffi-
cient to inoculate other rabbits with a very minute
quantity to cause their death. But Jaillard and
Leplat affirmed that the examination of that blood did
not reveal the existence of any microscopic organisms.
Paul Bert, on his part, had succeeded in destroying

o

194 LOUIS PASTEUR.

the bacteria by compressed oxygen, and yet the viru-
lence had continued.

Were there, then, two kinds of virus? What
escape was there from this darkness ? A new light
suddenly began to dawn. Pasteur had already some
years previously demonstrated that the animal body
is sealed against the introduction of lower organisms
— that in the blood, the urine, the muscles, the liver,
the spleen, the kidneys, the brain, the marrow, and
the nerves, in a normal state, no germ is found, or
particle of any kind, known or unknown, which could
be transformed into bacteria, vibrios, monads, or mi-
crobes. The intestinal canal alone is filled with
matters associated with a host of germs and living
products in process of development, and in divers states
of physiological action. Not only is its temperature
favourable to the life of infusoria, but it receives in-
cessantly matters charged with the germs of these mi-
croscopic organisms. To the upper portions of the
canal the air still has access, so that even in the
stomach aerobic microbes may be found, but in the
lower parts of the intestinal canal oxygen is absent,
and only anaerobic microbes can be developed there.
Although the life exerted in the mucous surface of the
intestines opposes itself to the passage of those little
organisms into the interior of the body, this ceases
to be the case after death. There is no longer any
obstacle to arrest or prevent them from acting accord-

VIRULENT DISEASES. 195

ing to the respective laws of their evolution and of the
decomposing influence which belongs to them. It is
by anaerobic organisms, in fact, that the putrefaction
•of dead bodies is begun. They penetrate into the
organs and into the blood as soon as this liquid is de-
prived of oxygen ; and it is not long before this
happens, the oxygen fixed in the globules being soon
consumed. In the body of an animal which has
died of splenic fever, putrefaction is still more rapid,
because, through the action of the disease, the blood is
already in a great degree deprived of oxygen at the
time of death. Nothing is more striking than the rapid
inflation and almost immediate putrefaction of animals
which have succumbed to splenic fever. Of all the
vibrios ready to pass from the intestinal canal into the
network of mesenteric veins which surround the canal
those which seem to take the foremost place are the
septic vibrios. These specially merit the name of
vibrios of putrefaction, from the very putrid gases
which result from their action upon nitrogenous and
sulphurous substances. The others diffuse themselves
more or less slowly in the blood, but the septic vibrio
takes almost immediate possession of the dead body.
Already after twelve or fifteen hours, the blood of the
diseased animal, which at the time of its death and
during the first following hours contained exclusively
the parasite of splenic fever, harbours at one and
.the same time both the bacillus of splenic fever

o 2

196 LOUIS PASTEUK.

and the septic vibrio. Then occur the very curious1
effects arising from the anaerobic nature of these
vibrios, and their opposition to the bacillus of splenic
fever, which is exclusively aerobic. Diffused in blood
deprived of oxygen gas, the splenic bacillus soon
perishes. In its place are to be found amorphous
granulations deprived of all virulence. The septic
anaerobic vibrio, on the contrary, finds itself after
death in the most favourable conditions for its life and
development. Not only does it penetrate into the
blood by the deep mesenteric veins, but also into the
liquids which ooze out of the abdomen and muscles.

From the antagonism existing between the physio-
logical peculiarities of the splenic bacilli and the septic
vibrio, it results that if, in order to inoculate an
animal capable of contracting the fever, a drop of blood
be taken from one that has just died of it, and if the
operation is performed during the first few hours after
death, it is certain to communicate to that animal
splenic fever, and splenic fever only. If, on the other
hand, the operation is performed after a greater
number of hours — say, between twelve and twenty, ac-
cording to the season of the year — then the inocula-
tion of the blood will communicate, at one and the
same time, splenic fever and septicaemia — acute septi-
caemia, as it may be called, because of the rapid
inflammatory disorders that the septic vibrio causes
in the inoculated animal. The two diseases may be

VIRULENT DISEASES. 197

-developed simultaneously in the inoculated animal,
but generally one precedes the other. The septic
contagium is the quickest in its action ; it generally
causes death before the splenic fever has had time to
develop itself and to produce appreciable effects.

We are now in a position to explain all the contra-
dictory results obtained by MM. Jaillarcl and Leplat on
one side, and by Davaine on the other. -In a country
which splenic fever had made famous, the Departement
d'Eure-et-Loir, they had asked for a little splenic
fever blood. Now, what takes place in a farm where
an animal has died of this disease ? The dead body
is thrown upon a dungheap, or into some shed or stall,
until the knacker's cart happens to pass. The knacker
takes his own time, and the body often remains there
twenty-four or forty-eight hours. The blood taken
from this animal is more or less invaded by putrefac-
tion, and vibrios are mingled with the bacteria of splenic
fever, the development of which is arrested the moment
the animal dies. In short, it may be easily conceived
that an experimenter writing to Chartres to procure
some splenic fever blood might, without his know-
ledge, or the knowledge of his correspondent, receive
blood at the same time both splenic and septic. And
this septicaemia is sometimes manifold, for a special
septicasmia may be said to correspond to every sort of
vibrio of putrefaction.

Such were the circumstances which, without their

198 LOUIS PASTEUR.

being aware of it, accompanied Jaillard and Leplat's
researches upon splenic fever infection. This impres-
sion will be derived from reading the successive
notes laid by them before the Academy of Sciences.
The blood of the cow which had died of splenic fever,
sent from the knacker's establishment of Sours, and the
blood of the sheep sent by M. Boutet, must both have
been taken from the bodies of animals which had been
dead a sufficient number of hours to render their blood
both splenic and septic ; and it was septicaemia, so
prompt in its action, that had killed the rabbits of
Jaillard and Leplat. As the examination of the blood
of these animals showed no signs of bacteria, they
had concluded, with great apparent truth, that the
inoculation of splenic blood could cause death without
any appearance of these organisms, even while the
blood used for inoculation was full of them. The
presence of septic vibrios in the blood of the inoculated
rabbits escaped their notice. When Davaine replied
that Jaillard and Leplat had not worked with pure
splenic blood he had hit upon the truth, but he could
not give plausible reasons for it. The contest was
carried on by experiments in which, on both sides, truth
and error were closely blended.

The work of M. Paul Bert, at the close of 1876,
was surrounded with circumstances no less complex.
To thoroughly understand them we must call to mind
Pasteur's discovery as to the mode of reproducing the

VIKULENT DISEASES. 199

anaerobic germs of putrefaction. These vibrios repro-
duce themselves by spores. In the vibrio of acute
septicaemia this is the mode of generation. Short or
long jointed filaments show themselves studded with
brilliant points, which are precisely the spores of
which we speak. Experience proves that these spores
resist perfectly the poisonous action of compressed
oxygen. Inoculating an animal with blood which is at
the same time septic and splenic, after the blood has
been compressed, the septic germs, remaining alive,
produce death, although neither bacteria nor filaments
may be perceptible in its blood at the moment of
death. It was likewise from Chartres that M. Paul
Bert obtained his supply of splenic fever blood. The
blood he had received was without doubt not only
splenic but also septic. The filaments of bacteria and
the filaments of septic vibrios had perished under the
influence of the compressed oxygen ; but the spores were
there, and the great pressure of oxygen gas had not
affected them. The new contagium which had
appeared, and which had killed the inoculated
animals, was due to these spores.

As regards the proof that this virulence in the
blood of the body of an animal which has died of
splenic fever is really the effect of the septic vibrio,
Pasteur, assisted by Joubert and a new assistant, M.
Chamberland, has given that proof, as he did in the
case of the bacterium of splenic fever, by resorting to

200 LOUIS PASTEUE.

the method of successive cultivations in an artificial
medium. These cultivations, however, of the septic
vibrio require very special precautions and conditions.
They should be carried on in as perfect a vacuum as
it is possible to obtain, or in contact with carbonic
acid gas without the presence of air. In contact
with air the cultivations of septic vibrios would prove
sterile, because the vibrio is exclusively anaerobic and
air kills it. If a spore of this organism could germi-
nate in contact with the air, the product of the germina-
tion would be at once arrested and would perish by
the action of the .oxygen. It is exactly the contrary
with the bacilli of splenic fever, which prove sterile in
a vacuum or in presence of carbonic acid gas. If one
of the spores of the splenic fever bacillus (for it also
produces spores) could germinate, the product of the
germination, deprived of free oxygen, would at once
perish. And, to mention in passing a very ingenious
experiment of Pasteur's, we thus obtain a means of
separating by culture the bacillus of splenic fever
from the septic vibrio when they are temporarily
associated together. If this mixture of pathogenic
organisms is cultivated in contact with the air, the
bacilli of splenic fever alone will be developed. If this
same mixture is cultivated without air, either in a
vacuum or in carbonic acid gas, the septic vibrio
alone will be developed. This device of culture is one of
the best which can be employed to demonstrate that the

VIRULENT DISEASES. 201

blood of a body dead from splenic fever possesses imme-
diately after death a single contagium, that of splenic
fever, and that twenty- four hours after death, on the
contrary, there are two contagia, that of splenic fever
and that of septicaemia.

Some months ago a very hot discussion arose be-
tween Pasteur and a commission formed principally of
professors of the veterinary school in Turin, regarding
the. facts above mentioned. One experiment, in the
success of which Pasteur was extremely interested,
had been made at this school. Instead of employing
pure splenic fever blood, free from all contagium, the
Italian professors, whether from ignorance of the pre-
ceding facts or from inadvertence, employed the blood
of a diseased sheep, which, from their own showing,
had been dead more than twenty-four hours. Pasteur
immediately wrote, pointing out that the commission
had done wrong in using blood which must have been
at the same time splenic and septic. The Turin pro-
fessors grew angry, and affirmed that this assertion of
Pasteur's was incorrect ; that this sheep's blood had
been studied with care, and that no filaments had been
found in it except those of splenic fever; and it would,
moreover, be marvellous, they added ironically, that
Pasteur from the depths of his laboratory in Paris
should be able to assert that this blood was mixed with
septic poison, whilst they, good observers, armed with

202 LOUIS PASTEUR.

a microscope, had had this sheep's blood under their
eyes. Pasteur contented himself with replying that his
assertion rested upon a principle, and that he was per-
fectly able, without having seen the blood of the sheep,
to affirm that under the conditions in which it had
been collected that blood was septic. A public corre-
spondence ensued, but no understanding could be
come to. Pasteur then offered to go himself to Turin,
in order to demonstrate upon as many bodies of sheep
dead of splenic fever as they would like to give him,
that the blood of these dead bodies— at the end of
twenty-four hours if in the month of March, and in
twelve or fifteen hours if in the month of June, would
be found to be both splenic and septic. Pasteur also
proposed, by appropriate cultures, to withdraw at
pleasure the splenic fever poison or the septic poison,
or the two together, at the choice of the Italians. The
Italians, however, shrank from Pasteur's proposal to pay
them a visit in order to convince them of their error.
The clearness and certainty of Pasteur's assertions
are celebrated, but what gives such authority to all
that he advances is, as M. Paul Bert once said, that
Pasteur's boldness of assertion is only equalled by
his diffidence when he has not experiment to back
him up. He never fights except on ground with
which he has made himself familiar, but then he
fights with such resolution, and sometimes with such
impetuosity, that one might say to his adversary, who-

VIRULENT DISEASES. 203

ever he be, ' Je vmis plains de tomber dans ses mains
redoutables.'

' Take care ! ' said a member of the Academy of
Sciences to a member of the Academy of Medicine,
who a short time after the incident just related was
proposing scientifically to * strangle ' Pasteur, ' take
care ! Pasteur is never mistaken.'

One day, in 1879, a professor attached to a faculty
of medicine in one of the provinces announced to the
Academy of Sciences that he had found, in the blood
of a woman who had died in a hospital after two
weeks' illness from severe puerperal fever, a considerable
number of motionless filaments, simple or jointed,
transparent, straight, or bent, which belonged to the
genus Leptothrix. Engaged in studies on puerperal
fever, and having never met with a fact of this kind in
his researches, Pasteur wrote at once to this professor
to ask him for a specimen of the infected blood. The
blood arrived at the laboratory, and some days after
Pasteur wrote to the doctor, * Your leptothrix is no-
thing else than the bacterium of splenic fever.'

This answer perplexed the doctor very much. He
wrote to Pasteur that he did not dispute the affirma-
tion, but that he proposed to control it ; that if he
found he had been in error he would publish it.

Pasteur offered to send him guinea-pigs which had
been inoculated with splenic fever. 'You will receive
them still living ; they will die under your eyes. You

204 LOUIS PASTEUK.

will make the autopsy and you will yourself recognise
your leptothrix.' The doctor accepted the test. Pasteur
inoculated three guinea-pigs, had them placed in a cage
and sent by rail to the professor. They arrived the
following morning and died twenty-four hours after-
wards under the doctor's own eyes. The first had
been inoculated with the infectious blood of the dead
woman, the second with the bacterium of splenic fever
blood from Chartres, the third with the blood of a cow
which had died of splenic fever in the Jura. At the
autopsy it was impossible to discover the slightest
difference in the blood of the three animals. Not only
the blood but the internal organs, and especially the
spleen, were in exactly the same condition.

Then, in the most honourable manner, the doctor
hastened to state, in a communication to the Academy
of Sciences, that he regretted doubly not having known
about splenic fever the year before, as he might have
been able, on the one hand, to diagnose the formid-
able complication which had manifested itself in the
woman who died on April 4, 1878, and, on the other
hand, to have traced out the mode of contamination
which now eluded him. He had, however, succeeded in
learning a few details regarding the unhappy woman.
She was a charwoman, and lived in a little room
adjoining the stables of a horse-dealer. Through
these stables a large number of horses passed con-
tinually.

VIRULENT DISEASES. 205-

But to return to our septic vibrios. If air de-
stroys them, if their culture is impossible in contact
with air, how can septicaemia exist, since air is every-
where present ? How can blood exposed to the air
become septic from particles of dust on the sur-
face of objects or which the air holds in suspension?
Where can the septic germs be formed ? The objec-
tion seems a serious one, but it disappears before a
very simple experiment. Take some serum from
the abdomen of a guinea-pig which has died of acute
septicaemia. It will be found full of septic vibrios
in process of generation by fission. Let this liquid
be then exposed to the contact of air, with the pre-
caution of giving a certain depth to the liquid —-say,
a centimeter of depth. In some hours, if examined
with the microscope, the following curious spectacle
will be witnessed : In the upper layers the oxygen of
the air is absorbed, which is manifested by the already
changed colour of the liquid. There the filamentous
vibrio dies, and disappears under the form of fine
amorphous granulations deprived of virulence. At the
bottom of this layer of one centimeter in thickness, on
the contrary, the vibrios, protected from the approach
of oxygen by those of their own kind which have
perished above them, continue to multiply by fission
until by degrees they pass into the state of spores ; so
that instead of moving threads of all dimensions, the
length of which sometimes even extends beyond the

206 LOUIS PASTEUR.

field of the microscope, nothing is now seen but a dust
of brilliant isolated specks, upon which the oxygen of
the air has no action. It is thus that a dust of septic
germs can be formed even in contact with air. And
thus it becomes possible to understand how anaerobic
organisms may be sown in putrescible liquids by the
dust suspended in the atmosphere. Thus also may
be explained the permanence of putrid diseases, even
of those which are caused by anaerobic microbes, that
cannot live in the atmosphere and which escape de-
struction by becoming spores.

By means of these experiments, as unexpected as
they were conclusive, Pasteur had demonstrated that
Jaillard and Leplat had not really inoculated their
rabbits with an amorphous virus, liquid or solid, but
with a virus constituted of a living microscopic organ-
ism— in other words, with a true ferment. By the
side of the parasite of splenic fever we have thus a
fresh example of a living animated virus, with germs
forming dust. And the extraordinary thing is that
among the microbes of special maladies — which they
produce by penetrating and multiplying in the bodies
of animals— are to be found aerobies like the bacilli of
splenic fever, and anaerobies like the vibrios of acute
septicaemia.

VIRULENT DISEASES. 207

II.

In these two virulent maladies, then, splenic fever
und septicaemia, the researches of Pasteur had clearly
established the parasitic theory. A grand and novel
opening was made for future studies on the origin of
diseases. Yet, judging from the surprising differences
which separate septicaemia and splenic fever, we can
foresee that should the future, copying the past, in
regard to this and still more recent discoveries, have
in store, as it no doubt has, the knowledge of new
microbes of disease, the specific properties of these
microscopic organisms will demand, for each new ex-
ploration, ceaselessly repeated efforts, not only to make
the existence of these organisms evident, but also to
furnish decisive proofs of their morbific power. But
the question which may be considered as already solved
is the non- spontaneity of these infectious microbes.
By what is called spontaneous disease is meant parasitic
disease. But in the present state of science sponta-
neous disease has no more existence than spontaneous
generation. Such aphorisms, however, are not allowed
to pass without occasional contradictions, all the more
vehement from their rarity. At the International
Medical Congress held in London, August 1881, Dr.
Bastian, who practises in one of the principal hospitals
of London, declared that though he was unable to

208 LOUIS PASTEUR.

deny the existence of parasitic diseases, yet, in his
opinion, the microbes were the effect and not the cause
of these diseases.

'Is it possible,' cried Pasteur, who was present at
the meeting, ' that at this day such a scientific heresy
should be held ? My answer to Dr. Bastian will be
short. Take the limb of an animal and crush it in a
mortar ; let there be diffused in this limb, around these
crushed bones, as much blood, or any other normal or
abnormal liquid as you please. Take care only that
the skin of the limb is neither torn nor laid open, and
I defy you to exhibit on the following day, or during
all the time the malady lasts, the least microscopic
organism in the humours of this limb.'

After the example of Liebig in 1870, Dr. Bastian
did not accept the challenge.

But if a disease like splenic fever is carried by a
microbe, this microbe is under the influence of the
medium in which it finds itself. It does not develop
everywhere. Easily inoculable and fatal to the ox,
the sheep, the rabbit, and the guinea pig, splenic fever
is very rare in the dog and in the pig. These must
be inoculated several times before they contract the
disease, and even then it is not always possible to
produce it. Again, there are some creatures which are
never assailable by it. It can never be taken by fowls.
In vain they are inoculated with a considerable quan-
tity of splenic blood; it has no effect upon them.

VIKULENT DISEASES. 209

This invulnerability had very much struck Pasteur
and his two assistants, Joubert and Chamberland.
What was it in the body of a fowl that enabled
it to thus resist inoculations of which the most in-
finitesimal quantity sufficed to kill an ox? They
proved by a series of experiments that the microbe
of splenic fever does not develop when subjected to
a temperature of 44° Centigrade. Now, the tempe-
rature of birds being between 41 and 42 degrees,
may it not be, said Pasteur, that the fowls are
protected from the disease because their blood is too
warm — not far removed from the temperature at which
the splenic fever organism can no longer be culti-
vated ? Might not the vital resistance encountered in
the living fowl suffice to bridge over the small gap
between 41-42, and 44-45 degrees ? For we must
always allow for a certain resistance in all living
creatures to disease and death. No doubt, life to
a parasite in the body of an animal would not be
as easy as in a cultivating liquid contained in a glass
vessel. If the inoculating microbe is aerobic, it can
only be cultivated in blood by taking away the oxygen
from the globules, which retain it with a certain
force for their own life. Nothing was more legitimate
than to suppose that the globules of the blood of the
fowl had such an avidity for oxygen that the fila-
ments of the splenic parasite were deprived of it, and
that their multiplication was thus rendered impossible.

210 LOUIS PASTEUR.

This idea conducted Pasteur and his assistants to new
researches. * If the blood of a fowl was cooled,' they
asked, * could not the splenic fever parasite live in this
blood?'

The experiment was made. A hen was taken, and,
after inoculating it with splenic fever blood, it was
placed with its feet in water at 25 degrees. The
temperature of the blood of the hen went .down to
87 or 38 degrees. At the end of twenty-four hours
the hen was dead, and all its blood was filled with
splenic fever bacteria.

But if it was possible to render a fowl assailable
by splenic fever simply by lowering its temperature,
is it not also possible to restore to health a fowl
so inoculated by warming it up again ? A hen was
inoculated, subjected, like the first, to the cold-water
treatment, and when it became evident that the fever
was at its height it was taken out of the water,
wrapped carefully in cotton wool, and placed in an
oven at a temperature of 35 degrees. Little by little
its strength returned; it shook itself, settled itself
again, and in a few hours was fully restored to health.
The microbe had disappeared. Hens killed after
having been thus saved, no longer showed the
slightest trace of splenic organisms.

How great is the light which these facts throw
upon the phenomenon of life in its relation to ex-
ternal physical conditions, and what important in-

VIRULENT DISEASES. 211

ferences do they warrant as to the influence of external
media and conditions upon the life and develop-
ment of living contagia ! There have been great dis-
cussions in Germany and France upon a mode of
treatment in typhoid fever, which consists in cooling
the body of the patient by frequently repeated baths.
The possible good effects of this treatment may be
understood when viewed in conjunction with the fore-
going experiment on fowls. In typhoid fever the cold
arrests the fermentation, which may be regarded as at
once the expression and the cause of the disease, just
as, by an inverse process, the heat of the body arrests
the development of the splenic fever microbe in the
hen.

p 2

212 LOUIS PASTEUR.

FOWL CHOLERA.

IF fowls are naturally impervious to the infection of
splenic fever, there is a disastrous malady to which
they are subject, and which is commonly called ' fowl
cholera.' Pasteur thus describes the disorder : — * The
bird which is attacked by this disease is without
strength, staggering, the wings drooping. The ruffled
feathers of the body give it the shape of a ball. An
overpowering somnolence takes possession of it. If
forced to open its eyes, it appears as if it were
awakened out of a deep sleep. Very soon the eyelids
close again, and generally death comes without the
animal changing its place, or without any struggle,
except at times a slight movement of the wings for a
few seconds.' The examination after death reveals
considerable internal disorders.

Here, again, the disease is produced by a micro-
scopic organism. A veterinary surgeon of Alsace,
M. Moritz by name, was the first who suspected the
presence of microbes in this disease; a veterinary
surgeon of Turin, M. Peroncito, depicted it in 1878 ;

FOWL CHOLEBA. 213

a professor of the veterinary school of Toulouse, M.
Toussaint, recognised it, in his turn, in 1879, and sent
to Pasteur the head of a cock which had died of
the cholera. But, however skilful they were, these
observers had not succeeded in deciding the question
of parasitism. None of them had hit upon a suitable
cultivating medium for the parasite, nor had they
reared it in successive crops. This, however, is the
only method of proving that the virulence belongs
exclusively to a parasite.

It is absolutely necessary, in the study of maladies
caused by microscopic organisms, to procure a liquid
where the infectious parasite can grow and multiply
without possible mixture of other organisms of differ-
ent kinds. An infusion of the muscles of the fowl,
neutralised by potash, and rendered sterile by a tem-
perature of 110 to 115 degrees, has proved to be
wonderfully appropriate to the culture of the microbe
of fowl cholera. The facility of its multiplication in
this medium is almost miraculous. In some hours
the clearest infusion begins to grow turbid, and is
found to be filled with a multitude of little organisms
of an extreme tenuity slightly strangulated at their
centres. These organisms have no movement of their
own. In some days they change into a multitude
of isolated specks, so diminished in volume that the
liquid, which had been turbid to the extent of resembling
milk, becomes again almost as clear as at first. The

214 LOUIS PASTEUE.

microbe here described belongs to a totally different
group from that of the vibrios. It is ranged under the
genus called ' micrococci.' 'It is in this group,' said
Pasteur on one occasion, * that the microbes of the
viruses which are yet unknown will probably be one
day found.'

In the cultivation of the microbe of fowl cholera,
Pasteur tried one of the cultivating liquids which he
had previously made use of with most success — the
water of yeast — that is to say, a decoction of yeast in
water rendered clear by nitration and then sterilised by
a temperature of over 100 degrees. The most diverse
microscopic organisms find in this liquid suitable
nourishment, particularly if it has been neutralised.
When, for example, the bacterium of splenic fever is
sown in the liquid, it assumes in a few hours a sur-
prising development. Now, it is remarkable that this
medium is quite unsuited to the life of the microbe of
fowl cholera. Not only does it not develop, but the
microbe perishes in this liquid in less than forty-eight
hours. May we not connect this singular fact with
that which is observed when a microscopic organism
proves innocuous in an animal which has been ino-
culated with it ? It is innocuous because it cannot
develop itself in the body of the animal, or because,,
its development being arrested, it cannot attain the
vital organs.

The decoction extracted from the muscles of the

FOWL CHOLEKA. 215

fowl is the only medium which really suits the mi-
crobe of fowl cholera. It suffices to inoculate the fowl
with the hundredth, even the thousandth, part of a
drop of this mixture, to produce the disease and cause
death. But here is a strange peculiarity. If guinea-
pigs are inoculated with this little parasite they are
hardly ever killed by it. Guinea-pigs of a certain age
generally exhibit only a local lesion at the point of
inoculation, which ends in an abscess more or less
prominent. After opening spontaneously, the abscess
closes again and heals, while the animal preserves its
appetite and its appearance of health. These abscesses
sometimes last several weeks. They are surrounded
by a pyogenic membrane and filled with a creamy
pus, in which the microbe swarms side by side with the
pus globules. It is the life of the microbe inoculated
under the skin which causes the abscess. The abscess,
with the membrane which surrounds it, becomes for
the little organism a sort of closed vessel, which it is
even easy to tap without sacrificing the guinea-pig.
The organism is mixed with the pus in a state of great
purity, and although it is localised its virulence is ex-
treme. When fowls are inoculated with the contents
of the abscess they die rapidly, while the guinea-pig,
which has furnished the virus, gets well without the
least suffering. A curious instance this is of the
local evolution of a very virulent microscopic organism,
which produces neither internal disorders nor the

216 LOUIS PASTEUR.

death of the animal upon which it lives and multiplies,
but which can carry death to other species inoculated
with it. Fowls and rabbits living among the guinea-
pigs suffering from these abscesses might in a moment
be smitten and perish, while the health of the guinea-
pigs remained unchanged. To produce this result it
would suffice that a little of the discharge from the
abscess of a guinea-pig should get smeared over the
food of the fowls and rabbits. An observer witnessing
such deaths without apparent cause, and ignorant of
this strange dependency, would no doubt be tempted
to believe in the spontaneity of the disease. He would
be far from supposing that the evil had originated in
the guinea-pigs, which were all in good health. In
the history of contagia what mysteries may some day
be cleared up by even more simple solutions than this
one !

When some drops of the liquid containing this
microbe are placed on the food of fowls, the disease
penetrates by the intestinal canal. There the little
organism increases in such great abundance that ino-
culation with the excrements of the injected fowls pro-
duces death. It is thus easy to account for the mode
of propagation of this very serious disease, which
depopulates sometimes all the poultry yards in the
country. The only means of arresting the contagion
is to isolate, for a few days only, the fowls and the
chickens, to remove the dung heaps, to wash the yard

FOWL CHOLEKA. 217

thoroughly, especially with water acidulated with a
little sulphuric acid, or carbolised water with two
grammes of acid to the litre. These liquids readily de-
stroy the microbe, or at least suspend its development.
Thus all causes of contagion disappear, because, during
their isolation, the animals already smitten die. The
action of the disease, in fact, is very rapid.

The repeated cultivation of the infectious microbe in
the fowl infusion, passing always from one infusion to
the next following, by sowing in the latter an infinitely
small quantity, so to speak, of the virus — as much, for
example, as may be retained on the point of a needle
simply plunged into the cultivation — does not sensibly
lessen the virulence of the microscopic organism. Its
multiplication inside the bodies of fowls is quite as
easy with the last as with the first culture. In short,
whatever may be the number of the successive cultures
of the microbe in the fowl infusion, the last culture is
still very virulent. This proves the microbe to be the
cause of the disease — a proof the same in kind as that
which had already enabled Pasteur to show that
splenic fever and septicaemia are produced by specific
microbes.

Like the bacillus of splenic fever, the microbe of
the fowl cholera is an aerobic organism. It is culti-
vated in contact with the air, or in aerated liquids.
At the same time, though it is entitled to be called an
aerobic organism, it differs essentially in certain re-

218 LOUIS PASTEUK.

spects from the parasite of splenic fever. If splenic
fever blood filled with filaments of the parasite be
enclosed in a vessel protected from the air — say, in a
tube closed at its two extremities — in a few days, eight
or ten at the most, and much fewer in summer, the
parasite disappears, or rather is reduced to fine amor-
phous granulations, and the blood loses all its viru-
lence. If the same system of shutting out the air be
employed with the blood of a fowl charged with the
microbe of fowl cholera, this microbe will be preserved
with its virulence for weeks, months, even years.
Pasteur has been able to keep for three years tubes
thus sealed, a drop of blood from which when culti-
vated in fowl infusion, sufficed to infect the birds in
the poultry yard with cholera. And not only is the
microbe preserved thus in the blood contained in the
tube; the same occurs if fowl infusion be put into
tubes and then sealed by the flame of a lamp.

When, in course of time, such tubes lose their
virulence, it is because the vitality of the organism is
extinct. The moment the contents of the tube cease
to be virulent, it is a sign that the contagium is dead.
It is useless, then, to attempt to cultivate it : the
microbe cannot be revived.

Here, then, is a third virulent disease, also produced
by a microscopic organism. The characteristics of fowl
cholera are very different from those of splenic fever
and acute septicernia, and these three microbes do not

FOWL CHOLEKA. 219

in the least resemble each other. But, glancing back
over Pasteur's work, are not the diseases of silkworms,
pebrine and flacherie, also virulent diseases ? Thus,,
in so many things, through so many studies, the same
connection holds good. Each discovery of Pasteur's is
linked to those which precede it, and is the rigorous
verification by experimental method of a preconceived
idea.

' Nothing can be done,' said he one day, ' without
preconceived ideas; only there must be the wisdom
not to accept their deductions beyond what experi-
ments confirm. Preconceived ideas, subjected to the
severe control of experimentation, are the vivifying
flame of scientific observation, whilst fixed ideas are
its danger. Do you remember the fine saying of
Bossuet ? " The greatest sign of an ill-regulated
mind is to believe things because you wish them to be
so." To choose a road, to stop habitually and to ask
whether you have not gone astray, that is the true
method.'

It is this method which conducted him in 1880
to that wonderful discovery, the attenuation of con-
tagia. What certain of these contagia are, we have
already seen. We shall now learn what they become
in the hands of Pasteur.

220 LOUIS PASTEUR.

THE ATTENUATED VIRUS, OR VACCINA-
TION OF VIRULENT DISEASES.

THE VACCINE OF FOWL CHOLERA.

AMONG the scourges which afflict humanity there are
none greater than virulent diseases. Measles, scar-
latina, diphtheria, small-pox, syphilis, splenic fever,
yellow fever, camp typhus, the plague of the East
— what a terrible enumeration ! I pass over some,
such as glanders, leprosy, and hydrophobia. The
history of these diseases presents extraordinary cir-
cumstances. The most strange, assuredly, is that
which has been from all time established with a great
number of these diseases, that they are non-recurrent.
As a general rule, notwithstanding some rare excep-
tions, man can only have measles, scarlet fever,
plague, yellow fever once. What explanation, even
hypothetically, can be given of such a fact? Still
more difficult is it to explain how vaccination, which is
itself a virulent though benign disease, preserves from
a more serious malady, the small-pox? Has there

THE ATTENUATED VIRUS, OB VACCINATION. 221

ever been a discovery more mysterious in its causes
and origin, standing, as it does, alone in the history
of medicine, and for more than a century defying all
comparison ?

After dwelling long on Jenner's discovery this ques-
tion arose in Pasteur's mind : If contagious maladies
do not repeat themselves, why should there not be
found for each of them a disease different from them,
but having some likeness to them, which, acting
upon them as cow-pox does upon small-pox, would
have the virtue of a prophylactic ? A chance occur-
rence, one of those chances which not unfrequently
occur to those who are steadfastly looking out for
them, opened out to Pasteur the way to a discovery
which may well be called one of the greatest discoveries
of the age.

In causing the microbe of fowl cholera to pass from
culture to culture, in an artificial medium, a sufficient
number of times to render it impossible that the least
trace of the virulent matter from which it originally
started should still exist in the last cultivation,
Pasteur gave in an absolute manner the proof that
infectious microbes are the sole authors of the
diseases which correspond to them. This culture may
be repeated ten, twenty, a hundred, even a thousand
times : in the latest culture the virulence is not ex-
tinguished, or even sensibly weakened. But it is a
fact worthy of attention that the preservation of the

'222 LOUIS PASTEUR.

virulence in successive cultures is assured only when
no great interval has been allowed to elapse between
the cultures. For example, the second culture must
be sown twenty- four hours after the first, the third
twenty-four hours after the second, the hundredth
twenty- four hours after the ninety-ninth, and so on.
If a culture is not passed on to the following one
until after an interval of several days or several
weeks, and particularly if several months have
elapsed, a great change may then be observed in
the virulence. This change, which generally varies
with the duration of the interval, shows itself by the
weakening of the power of the contagium.

If the successive cultures of fowl cholera, made at
short intervals, have such virulence that ten or twenty
inoculated birds perish in the space of twenty-four
or forty-eight hours, a culture which has remained,
say, for three months in its flask, the mouth of which
has been protected from the introduction of all foreign
germs by a stopper of cotton wool, which allows
nothing but pure air to pass through it — this culture,
if used to inoculate twenty fowls, though it may
render them more or less ill, does not cause death in
any of them. After some days of fever they recover
both their appetite and spirits. But if this phenome-
non is extraordinary, here is one which is surely
in a different sense singular. If after the cure of
these twenty birds they are reinoculated with a very

THE ATTENUATED VIRUS, OK VACCINATION. 223

virulent virus — that, for instance, which was just now
mentioned as capable of killing its hundred per cent,
of those inoculated with it, in twenty-four or forty-
eight hours — these fowls would perhaps become rather
ill, but they would not die. The conclusion is simple ;
the disease can protect from itself. It has evidently
that characteristic of all virulent diseases, that it
cannot attack a second time.

However curious it may be, this characteristic is
not a thing unknown in pathology. Formerly it was
the custom to inoculate with small-pox to preserve
from small-pox. Sheep are still inoculated to preserve
them from the rot ; to protect horned cattle from
peripneumonia they are inoculated with the virus of
the disease. Fowl cholera offers the same immunity ;
it is an additional scientific acquisition, but not a
novelty in principle.

The great novelty which is the outcome of the
preceding facts, and which gives them a distinct
place in our knowledge of virulent diseases, is that we
have here to do with a disease of which the virulent
agent is a microscopic parasite, a living organism
cultivated outside of the animal body, and that the
attenuation of the virulence is in the power of the
experimenter. He creates it, he diminishes it, he
does what he wishes with it ; and all these variable
virulences he obtains from the maximum virulence
by manipulation in the laboratory. Looked at in

224 LOUIS PASTEUK.

juxtaposition with the great fact of vaccination for
small-pox, this weakened microbe, which does not
cause death, behaves like a real vaccine relatively to
the microbe which kills, producing a malady which
may be called benign, since it does not cause death,
but is a protection from the same malady in its more
deadly form.

But for this enfeebled microbe to be a real vaccine,
comparable to that of cow-pox, must it not be fixed, so
to speak, in its own variety, so that there should be
no necessity for having recourse again to the pre-
paration from which it was originally derived?
Jenner, when he had demonstrated that cow-pox
vaccination preserved from small- pox, feared for some
time that it would be always necessary to have
recourse to the cow to procure fresh vaccinating
matter. His true discovery consisted in establishing
that the cow-pox from the cow could be dispensed
with, and that inoculation could be performed from
arm to arm. Pasteur made his enfeebled microbe
pass from one cultivation to another. What would it
become ? Would it resume its very active virulence,
or would it preserve its moderate virulence ?

The virulence remained enfeebled and, we may say,
unchanged. This showed it to be a real vaccine.
Some veterinary surgeons and farmers, on the an-
nouncement of this discovery, applied to Pasteur for
a vaccine against the disease which was so disastrous

THE ATTENUATED VIRUS, OK VACCINATION. 225

among their poultry. Some trials were made, and
all succeeded beyond expectation. To preserve this
vaccine it must be secured from contact with the air,
the cultures being enclosed in tubes, the extremities
of which are sealed by the flame of a blowpipe.

What takes place during that interval of time in-
tentionally placed between two successive cultivations
of the cholera microbe — that interval which is em-
ployed in effecting the attenuation and producing the
vaccine ? What is the secret of this result ? The
agent which intervenes is no other than the oxygen
of the air. Here is the proof. If the cultivation of
this microbe is carried on in a tube containing very
little air, and if the tube is then closed by the flame
of a lamp, the microbe, by its development and life,
quickly appropriates all the free oxygen contained in
the tube, as well as the oxygen dissolved in the liquid.
Thus, completely protected from contact with oxygen,
the microbe does not become sensibly weakened for
months, sometimes even for years.

The oxygen of the air, then, appears to be the
cause of modification in the virulence of the microbe.

But how, then, is the absence of influence on the
part of the atmospheric oxygen, in the successive cul-
tures which are practised every twenty-four hours, to
be explained ? There is, in Pasteur's opinion, but one
possible explanation ; it is that the oxygen of the air
in this latter case is solely employed in the life of the

Q

226 LOUIS PASTEUR.

microbe. A culture has a duration of some days ; in
twenty-four hours it is not terminated. The air which
comes in contact with it is then entirely employed
in nourishing and largely reproducing the microbe.
During the longer intervals of culture, the air acts
only as a modifier, and at last there arrives a moment
when the virulence is so much weakened as to become
nil.

This very extraordinary fact is, then, established
that the virulence may be entirely gone while yet
the microbe lives. The cultures offer the spectacle of
a microbe indefinitely cultivable, yet, on the other
hand, incapable of living in the bodies of fowls, and
in consequence deprived of virulence. May not this
domesticated microbe, as M. Bouley calls it, be com-
pared to those inoffensive microbes of which there
are so many in nature ? May not our common mi-
crobes be those organisms which have lost their former
virulence? But may not these harmless microbes,
become infectious in some particular circumstances ?
And if there are fewer virulent maladies now than
there were in times past, might not the number of
these maladies again increase ?

Questions multiply as the facts relating to the
attenuation of a virus suggest inductions, awaken
ideas, and throw new lights upon a problem which,
until within these last few years, has remained so
obscure. Formerlv it was believed that these viruses

THE ATTENUATED VIRUS, OK VACCINATION. 227

were morbid entities. A virus was a unity. This
opinion has still its declared upholders. According to
Pasteur a virus has different degrees of virulence ; it
can pass from the weakest virulence to the maximum.
Modifying, at will, the virus of fowl cholera, Pasteur
inoculates some hens, for instance, with a virus too
attenuated to protect from death, but which neverthe-
less is effectual in securing them against a virus
stronger than itself. The second virus will preserve
them from the attacks of a third virus, and thus
passing from virus to virus they end by being gua-
ranteed against the most deadly virulences. The whole
question of vaccination resolves itself into knowing
at what moment a certain degree of virus attenuation
is a guarantee of protection against the mortal virus.

It seems that between small-pox and cow-pox facts
•of a similar kind take place. It is probable that
vaccination rarely gives perfect security against the
infection of a very malignant small-pox; moreover,
during epidemics of small-pox many persons who have
been previously vaccinated are attacked, and some
<even die of the disease.

As regards the practice of vaccinating fowls against
the cholera peculiar to them — which, though it cer-
tainly is not of the same importance as human vac-
cination, is a scientifically capital fact — we may hope
that whatever the differences of receptivity in different
races, or in different individuals of the same race,

Q 2

228 LOUIS PASTEUR.

there will be found vaccines to suit them all, special
care being taken to resort to the employment of two
successive vaccines of unequal power, employed after
an interval of ten or fifteen days. The first vaccine
may always be chosen of a degree of weakness which
will not in any case cause death, and yet of sufficient
strength to prevent dangerous consequences from the
second vaccine, which would in some cases be fatal
if employed at once, and to enable it to act as a
vaccine against the most virulent virus.

With regard to the preparation of vaccines, and the
ascertaining of their proper strength, it is necessary to
make trials upon a certain number of fowls, even at
the risk of sacrificing a few in these preliminary
experiments. Beyond such questions of manipula-
tion there remains still a scientific question. How
are the effects of vaccination to be conceived ? What
explanation can be given of the fact that a benign
disease can preserve from a more serious and deadly
one ? Pasteur long sought for the solution of this
problem. Without flattering himself that he has un-
ravelled the difficulty, he has nevertheless amassed
facts which, amid these physiological mysteries, per-
mit us to frame a hypothesis which can satisfy the
mind. Pasteur believes, for example, that the vaccine,
when cultivated in the body of the animal, robs the
globules of the blood, for example, of certain material
principles which the vital actions take a long time to

THE ATTENUATED VIEUS, OK VACCINATION. 229

restore to the system, and which to the most deadly
contagium is a condition of life. The impossibility
of action of the progressive virus and of the deadly
virus is thus accounted for.

When Pasteur communicated to the Academy of
Sciences these important and unforeseen facts, they
were at first received with hesitation. It was not
without some surprise that the word vaccination,
hitherto exclusively reserved for Jenner's discovery,
was heard applied to fowl cholera. At the Inter-
national Medical Congress held in London in August
1881, Pasteur, in the presence of 3,000 doctors
of medicine from all parts of the world, who received
him with an enthusiasm which reflected glory on
France, justified the name that he had given to his
prophylactic experiments.

' I have lent,' he said, ' to the expression vaccina-
tion an extension that I hope science will consecrate,
as a homage to the merit and immense services
rendered to humanity by one of the greatest men of
England — Jenner.'

Still, while rendering homage to the sentiment
which induced Pasteur to efface himself in favour of
Jenner, we may be permitted to say that there is no
likeness between the two discoveries. Great as was the
discovery of Jenner, it was but a chance observation,
which had no ulterior development ; and for a whole
century, medicine has not been able to derive anything

230 LOUIS PASTEUR.

from it beyond its actual application, which is the one
result achieved. 'Vaccination is vaccination,' an
opponent of Pasteur's, who was driven hard, was
obliged to say. The opponent found no other answer,
and he could not have found any other. The cow-pox
is a malady belonging exclusively to a race of animals.
Man can only observe it ; he cannot produce it. Sup-
press cow-pox and there will be no more vaccination.
In the French discovery, on the contrary, it is the
deadly virus itself which serves as a starting point for
the vaccine. It is the hand of man which makes the
vaccine, and this vaccine may be artificially prepared
in the laboratory, in sufficient quantity to supply all
needs. What a future is presented to the mind in the
thought that the virus and its vaccines are a living
species, and that in this species there are all sorts of
varieties susceptible of being fixed by artificial cultiva-
tion ! The genius of Jenner made a discovery, but
Pasteur discovered a method of genius.

' This is but a beginning,' said M. Bouley on the
day when Pasteur announced these facts to the
Academy of Sciences. ' A new doctrine opens itself in
medicine, and this doctrine appears to me powerful
and luminous. A great future is preparing ; I wait
for it with the confidence of a believer and with the
zeal of an enthusiast.'

231

THE VACCINE OF SPLENIC FEVER.

WE have seen how the facts have been established
with regard to the microbe of fowl cholera. Immu-
nity against a virulent disease may be obtained by
the influence of a benign malady which is induced by
the same microbe, only weakened in virulence. What
a future there would be for medicine if this method
could be applied to the prevention of all virulent
diseases ! As splenic fever was at that time being
studied in the laboratory of the Ecole Normale, it was
upon this fever that the research was first attempted.
But the success of this research, said Pasteur, can
only be hoped for if the disease is non-recurrent. It
is only in this case that inoculation with the weakened
microbe can protect from the deadly splenic fever.
Unfortunately, human medicine is dumb as regards this
question of non-recurrence. The man who is smitten
with malignant pustule rarely recovers. If there are
any cases of recovery — and there are some authentic
ones — he who has so narrowly escaped death could
not confidently count upon his chance of protection

LOUIS PASTEUR.

from the disease in future. In order to acquire such
a sense of security he would have to expose himself to
experiments of direct inoculation, which he would
hardly care to do. Animals alone offer the possibility
of solving this problem. Yet it is not to all species
of animals that we can have recourse. Every sheep
inoculated with splenic fever infection is a sheep lost ;
but the ox and the cow have more power of resistance.
Among them there are frequent cases of cure. An
incident occurred which enabled Pasteur to push very
far this experimental study.

In 1879 the Minister of Agriculture appointed him
to give judgment upon the value of a proposed mode
of cure for cows smitten with splenic fever, which had
been devised by M. Louvrier, a veterinary surgeon of
the Jura. Choosing M. Chamberland as his assistant
to watch the application of M. Louvrier's remedy,
Pasteur instituted a series of comparative experiments.
Some cows were inoculated, two and sometimes four
at a time, with the virulent splenic fever virus. Half
of these cows were treated by M. Louvrier's method ;
the other half were left without treatment. A certain
number of the cows under M. Louvrier's care resisted
the disease, but an equal number of those not under
treatment recovered also. The inefficacy of the
remedy was demonstrated as well as the cause of the
inventor's illusions. But one precious result remained
from the trial of this remedy. Pasteur and Chamber-

THE VACCINE OF SPLENIC FEVEK. 233

land had thus at their disposition several cows which
had recovered from splenic fever, and which had ex-
perienced in their attack all the worst symptoms. At
the places of inoculation enormous swellings were
formed, which extended to the limbs, or under the
abdomen, and which contained several quarts of
watery fluid. The fever had been intense, and at one
time death had appeared imminent. When these
cows recovered they were reinoculated with great
quantities of virulent virus. Not the least trace of
disease showed itself, even in cases where the inocula-
tion was performed after an interval of more than a
year.

The question was solved ; splenic fever, like most
of the virulent diseases which it has been possible to
study, was non-recurrent. The immunity obtained
has a long duration. With that valiant ardour
which always urges him on, Pasteur next proposed
to examine the vaccine of splenic fever. In view
of these new investigations, which would require
long and careful labours, and which necessitated a
certain amount of medical knowledge, Pasteur asso-
ciated with himself, in addition to M. Chamberland,
a young savant, now a doctor of medicine, M.
Roux.

Following the rigorous course of his deductions,
Pasteur naturally turned to the oxygen of the air in
Iris attempts to modify the virulence of the splenic

234 LOUIS PASTEUK.

microbe. But a difficulty presented itself at the out-
set. Between this microbe and the microbe of fowl
cholera there exists an essential difference. The
microbe of fowl cholera, as is the case with a great
number of microscopic organisms, reproduces itself
only by fission. The parasite of splenic fever, on
the contrary, has another mode of generation ; it
forms spores, nothing analogous to which is found
in the microbe of cholera.

In the blood of animals, as in the cultures at the
beginning, the splenic fever microbe appears at first
in transparent filaments, more or less divided into
segments. Up to that point, the resemblance between
the microbe of splenic fever and the microbe of cholera
is complete. But this blood, or the cultures exposed
to the free contact of the air, instead of continuing
this first mode of generation, frequently exhibit, even
in the course of twenty-four hours, spores distributed
more or less regularly along the length of the fila-
ments. All around these corpuscles the matter of the
filaments is absorbed, in the manner formerly illustrated
by Pasteur in the diagrams of his work on the diseases
of silkworms, when treating of the bacilli of putrefac-
tion. Little by little, all cohesion between the spores
disappears, and the whole collection soon forms no-
thing more than a dust of germs. But—and here lies
the great difficulty which experimenters encountered
in applying to splenic fever the method of gradual

THE VACCINE OF SPLENIC FEVER. 235

attenuation which was practised with the microbe of
cholera — these germs of splenic fever may be exposed
for years to the air without losing their virulence,
always ready to reproduce themselves without any
appreciable change, and to manifest their effects in
the bodies of animals. How can it be hoped to dis-
cover a vaccine of splenic fever by the method used
with the contagium of fowl cholera, since the splenic
fever virulence, at the end of twenty-four hours, is con^
centrated in a spore ? Before the oxygen of the air has
had time to attenuate the contagium, the virulence of
the parasite would be encased in these spores. Yet
this objection did not appear insuperable to Pasteur.
Since (said he to himself), under its filamentous form,
the microbe of splenic fever is quite analogous to the
microbe of fowl cholera, may not the problem of ex-
posing the splenic microbe to the air be reduced to
the following one : to determine the conditions which
would prevent the production of spores ? The diffi-
culty would thus be surmounted ; for, once we have
got rid of the spores, the splenic filaments might be
maintained in contact with air for any length of time,
and we might then no doubt fall back upon the con-
ditions which had produced the attenuation of the
cholera microbe.

Pasteur and his two assistants gave themselves up
to this research. Days passed and experiments were
multiplied. Pasteur became more and more en-

236 LOUIS PASTMJK.

grossed : he had, what his daughter called, ' the face
of an approaching discovery.'

' Ah ! what a grand thing it would be,' he was
heard from time to time to murmur to himself with a
suppressed voice, ' if one could arrive at that — if the
fact that the attenuation of the microbe of fowl
cholera proved not to be an isolated one ! ' But if
anyone ventured to ask him a timid question as to
the phase his experiments were going through, he
would reply, 'No, I can tell you nothing. I dare
not express aloud what I hope.'

At last one day he came up from his laboratory
with a triumphant face. His joy was such that tears
stood in his eyes. I have never seen a more radiant
expression of the highest and most generous emotions
than emanated from his countenance.

' I should never console myself,' he said while em-
bracing us, * if a discovery such as my assistants and
I have just made were not a French discovery.'

And with the clearness which is the charm of this
powerful mind, he related to us the most recent dis-
coveries of his laboratory.

In neutralised chicken infusion the splenic microbe
•can no longer be cultivated at a temperature of 44
or 45 degrees. Its cultivation, on the contrary, is
easy at 42 or 43 degrees ; and in these conditions the
microbe produces no spores. At this latter tempera-

THE VACCINE OF SPLENIC FEVEK. 237

ture, therefore, and in contact with pure air, we can
maintain a culture of filamentous parasites of splenic
fever, deprived of all germs. In some weeks the crop
dies — that is to say, when this culture is sown in fresh
broth the sterility of the broth remains complete. But
during the preceding days life exists in the cultivating
liquid. If after two, four, six, or eight days of ex-
posure to the air and to heat, the contagium is tried
upon animals, its virulence is found to be continually
changing with the time of its exposure to the air,
and, consequently, it represents a series of attenuated
contagia. From the moment when the formation of
the spores of the splenic fever bacillus is prevented,
all becomes substantially the same as in the case of
the microbe of fowl cholera. Moreover, as in the
cholera microbe, each of these states of attenuated
virulence can be reproduced by cultivation. Finally,
splenic fever not being recurrent, each of these splenic
fever microbes constitutes a vaccine for the more
virulent microbe.

In order to apportion the virulence of the vaccine
to the species it is desired to vaccinate, it must be
tried on a certain number of individuals of the same
species. If some vaccinated animals are inoculated
with the virulent virus, and none of them perish, the
vaccine is good. Among individuals of the same
species, however, the difference of receptivity is in
general great enough to make it prudent, and even

238 LOUIS PASTEUR.

necessary, to have recourse to two vaccines, one weak
and the other stronger, with an interval of from 12 to
15 days between the two inoculations.

It was on February 28, 1881, that Pasteur com-
municated to the Academy of Sciences, in his own
name, and in those of his two fellow workers, the
exposition of this great discovery. Loud applause
burst forth with patriotic joy and pride. And yet so
marvellous were these results that some colleagues
could not help saying, ' There is a little romance in
all this.' All this reminds one, in fact, of what the
alchemist of Lesage did to the demons which annoyed
him. He shut them up in little bottles, well corked,
and so kept them imprisoned and inoffensive. Pasteur
shut up in glass bulbs a whole world of microbes, with
all sorts of varieties which he cultivated at will. Viru-
lences attenuated or terrible, diseases benign or deadly,
he could offer all. Hardly had the journals published
the compte-rendu of this communication when the
President of the Society of Agriculture in Melun, M.
le Baron de la Kochette, came, in the name of the
Society, to invite Pasteur to make a public experiment
of splenic fever vaccination.

Pasteur accepted. On April 28 a sort of conven-
tion was entered into between him and the Society.
The Society agreed to place at the disposal of Pasteur
and his two young assistants, Chamberland and Roux,

THE VACCINE OF SPLENIC FEVER 239

sixty sheep. Ten of these sheep were not to receive
any treatment; twenty-five were to be subjected to
two vaccinal inoculations at intervals of from twelve
to fifteen days, by two vaccines of unequal strength.
Some days later these twenty-five sheep, as well as
the twenty-five remaining ones, were to be inoculated
with the virus of virulent splenic fever. A similar ex-
periment was to be made upon ten cows. Six were to
be vaccinated, four not vaccinated ; and the ten cows
were afterwards, on the same day as the fifty sheep, to
receive inoculation from a very virulent virus.

Pasteur affirmed that the twenty-five sheep which
had not been vaccinated would perish, while the
twenty-five vaccinated ones would resist the very
virulent virus; that the six vaccinated cows would
not take the disease, while the four which had not
been vaccinated, even if they did not die, would at least
be extremely ill.

As soon as the agricultural and scientific press
had published this programme, and recorded Pasteur's
prophecies, several of his colleagues at the Academy of
Sciences, startled by such boldness in reference to a
subject which had hitherto been enveloped in such
profound obscurity, and fearing to see the illustrious
company somewhat compromised by these affirmations
in relation to problems of physiology and pathology,
addressed some observations to M. Pasteur on what
they called * a scientific imprudence. 'X

240 LOUIS PASTEUR.

' Take care,' they said to him, * you are commit-
ting yourself without possibility of retreat. Your
experiments in the laboratory hardly authorise you to
attempt experiments like those at Melun.'

' No doubt,' Pasteur answered, ' we have never
had in our experimental studies so many animals at
our disposition to inoculate ; but I have full confi-
dence. What has been already done in my laboratory
is to me a guarantee of what can be done.'

And M. Bouley, confident also in the assurances
of his illustrious friend, and arranging to meet him,
to witness these audacious experiments, said to his
anxious colleagues, ' Fear nothing ; he will come back
triumphant.'

The experiments began on May 5, 1881, at four
kilometers' distance from Melun, in a farm of the
commune of Pouilly-le-Fort, belonging to a veterinary
doctor, M. Kossignol, secretary-general of the Society
of Melun. At the desire of the Society of Agriculture,
a goat had been substituted for one of the twenty-five
sheep of the first lot. On the 5th of May they inocu-
lated, by means of the little syringe of Pravaz — that
which is used in all hypodermic injections — twenty-
four sheep, the goat, and six cows with five drops of
an attenuated splenic virus. Twelve days after, on
May 17, they reinoculated these thirty-one animals
with an attenuated virus, which was, however,
stronger than the preceding one.

THE VACCINE OF SPLENIC FEVER. 241

On May 31 very virulent inoculation was effected.
Yeterinary doctors, inquisitive people, and agricul-
turists formed a crowd round this little flock. The
thirty-one vaccinated subjects awaiting the terrible
trial stood side by side with the twenty-five sheep
and the four cows, which awaited also their first turn
of virulent inoculation. Upon the proposal of a
veterinary doctor, who disguised his scepticism under
the expressed desire to render the trials more com-
parative, they inoculated alternately a vaccinated and
a non- vaccinated animal. A meeting was then ar-
ranged by Pasteur and all other persons present for
Thursday, June 2, thus allowing an interval of forty-
eight hours after the virulent inoculation.

More than two hundred persons met that day at
Melun. The Prefect of Seine-et-Marne, M. Patinot,
senators, general counsellors, journalists, a great
number of doctors, of veterinary surgeons, and
farmers ; those who believed, and those who doubted,
came, impatient for the result. On their arrival at
the farm of Pouilly-le-Fort, they could not repress
a shout of admiration. Out of the twenty-five sheep
which had not been vaccinated, twenty-one were dead ;
the goat was also dead ; two other sheep were dying,
and the last, already smitten, was certain to die that
very evening. The non-vaccinated cows had all volu-
minous swellings at the point of inoculation, behind
the shoulder. The fever was intense, and they had

&

242 LOUIS PASTEUR.

no longer strength to eat. The vaccinated sheep were
in full health and gaiety. The vaccinated cows
showed no tumour ; they had not even suffered an
elevation of temperature, and they continued to eat
quietly.

There was a burst of enthusiasm at these truly
marvellous results. The veterinary surgeons especi-
ally, who had received with entire incredulity the an-
ticipations recorded in the programme of the experi-
ments, who in their conversations and in their journals
had declared very loudly that it was difficult to believe
in the possibility of preparing a vaccine capable of
triumphing over such deadly diseases as fowl cholera
and splenic fever, could not recover from their sur-
prise. They examined the dead, they felt the living.

' Well/ said M. Bouley to one of them, ' are you
convinced? There remains nothing for you to do
but to bow before the master,' he added, pointing to
Pasteur, ' and to exclaim —

" I see, I know, I believe, I am undeceived." '

Having suddenly become fervent apostles of the
new doctrine, the veterinary surgeons went about
proclaiming everywhere what they had seen. One
of those who had been the most sceptical carried
his proselytising zeal to such a point that he wished
to inoculate himself. He did so with the two first
vaccines, without other accident than a slight fever.

THE VACCINE OF SPLENIC FEVER. 243

It required all the efforts of his family to prevent him
from inoculating himself with the most virulent virus.

An extraordinary movement was everywhere pro-
duced in favour of vaccination. A great number of
agricultural societies wished to repeat the celebrated
experiment of Pouilly-le-Fort. The breeders of cattle
overwhelmed Pasteur with applications for vaccine.
Pasteur was obliged to start a small manufactory for
the preparation of these vaccines in the Eue Vauquelin,
a few paces from his laboratory. At the end of the
year 1881, he had already vaccinated 33,946 animals.
This number was composed of 32,550 sheep, 1,254
oxen, 142 horses. In 1882, the number of animals
vaccinated amounted to 399,102, which included
47,000 oxen and 2,000 horses. In 1883, 100,000
animals were added to the total of 1882.

From the commencement of the practical appli-
cation of this new system, the results were topical.
Among flocks where half had been vaccinated and
the other half not vaccinated — all the animals con-
tinuing to live together — the mortality from splenic
fever in 1881 was ten times less in the vaccinated
sheep than in the non-vaccinated, being 1 in 740
as against 1 in 78 ; and in cows and oxen fourteen
times less, being 1 in 1,254 against 1 in 88. In 1882
also, the mortality was ten times greater among the
.non- vaccinated than among the vaccinated animals.

In 1883 it was proved that the duration of the

R 2

244 LOUIS PASTEUR.

immunity generally lasted longer than a year. It isr
however, prudent to vaccinate every year, and to
select for performing the operation a period when
splenic fever has not yet become developed — in March
and April. If the vaccinating is postponed until the
fever is in the sheepfolds, there is the risk of attri-
buting to vaccination the losses which in reality
belong to the natural disease. Just as human vacci-
nation cannot preserve from small-pox a patient who
is already under the influence of small-pox, so the
eplenie vaccinations are powerless against a fever
already in process of incubation.

It must not be assumed that the duration of im-
munity to animals after splenic vaccination cannot be
compared with the duration of immunity from small-
pox after Jennerian vaccination. Jenner and his con-
temporaries believed that vaccination was able to
preserve from small-pox during the whole life. That
illusion disappeared long ago, and now ten years has
been fixed as the average duration of that immunity
and of the interval which ought to separate successive
vaccinations. This interval, moreover, is too long for
a certain number of individuals. Besides, in order to
judge of the immunity, of antisplenic vaccination, we
must not lose sight of the formidable trial which
vaccinated animals have to undergo when inoculated
with the most virulent virus. What doctor would
dare to subject a vaccinated child to inoculation from

THE VACCINE OF SPLENIC FEVEK. 245

virulent small-pox a year after its vaccination ?
Finally, taking into consideration the commercial and
economic view of the life of a sheep — if such an ex-
pression may be used — the average scarcely exceeds
three years. The duration, then, of the immunity
that vaccination confers is about a third of the dura-
tion of the animal's life.

246 LOUIS PASTEUK.

THE RETUEN TO VIRULENCE.

AFTER having reduced the microbes of fowl cholera
and splenic fever to all degrees of virulence, and
brought them to a point where they could no longer
multiply in the bodies of animals inoculated with
them, and fixed them in media appropriate to their
life, Pasteur asked himself whether it would not be
possible to restore to these attenuated microbes —
weakened to such a degree as to have lost all viru-
lence— a deadly virulence, and to render them again
capable of living and multiplying in the bodies of
animals.

Experiment soon confirmed this mental previ-
sion. An attenuated splenic fever virus which could
cause no danger of disease or death to guinea-pigs of
a year, or a month, or even a week old, could kill a
little guinea-pig just born, or one or two days old.
The attenuated microbe could multiply itself in the
blood of so young an animal. We can well imagine
that in an animal, scarcely formed, the power of oxy-
genation of the blood globules is not as yet capable of

THE RETURN TO VIRULENCE. 247

preventing the aerobic microbe from turning to its
own account the oxygen of the blood. The disease
does its work and death supervenes.

After all, there is nothing surprising in the fact
that the vital resistance of a newly-born guinea-pig
should differ from that of an adult one. But what is
very remarkable is, that if an older guinea-pig be
inoculated with the blood of one a day old ; if a third,
still older, be inoculated with the blood of the second ;
and so on ; the virulence of the microbe will be gradu-
ally reinforced — that is to say, the usual habit of this
parasite to develop itself in the body of the animal
will be restored. The process may be likened to that
of an animal or vegetable species, passing by successive
stages and long sojourns, from one region to another
very distant one, subjected to quite new conditions of
climate, and gradually becoming acclimatised to the
last one. How great, then, must be the importance
of the medium of cultivation, with regard to the viru-
lence of the microbes of communicable diseases !
Cultivating the microbe by passing it from one guinea-
pig to another, we soon arrive at a strength capable
of killing guinea-pigs of a week, a month, or several
years old, until at last the smallest drop of the blood
of these guinea-pigs suffices to kill a sheep ; and from
the sheep we may pass on to the ox.

The same is the case with the microbe of fowl
cholera. When it has ceased to have any effect upon

248 LOUIS PASTEUK

fowls, its virulence can be restored by inoculating
small birds. Blackbirds, canaries, sparrows, all die,
if the virus has not been too much attenuated ; and
the effect is similar on young chicks. Thus by
several successive transitions from bird to bird a viru-
lence may be fostered capable of destroying full-grown
fowls.

These facts suggested to Pasteur certain inductions
which may be well founded. Is not the attenuation of
the virus by the influence of the air one of the factors
in the extinction of great epidemics ? And may not
the reappearance of these scourges be accounted for
by the reinforcement of the virulence ?

* The accounts which I have read/ Pasteur re-
marked some months ago, ' of the spontaneous appear-
ance of the plague in Benghazi in 1856 and in 1858
tend to prove that this outbreak could not be traced
to any original contagion. Let us suppose, guided by
the facts now known to us, that the plague, a malig-
nant disease belonging to certain countries, has germs
of long duration. In all these -countries its attenuated
virus must exist, ready to resume its active form
whenever the conditions of climate, of famine, of
misery present themselves afresh. The condition of
long duration in the vitality of the germs of evil is
not even indispensable; for, if I may believe the
doctors who have visited these countries, in all places
subject to the plague, and in the intervals of the

THE EETUEN TO VIRULENCE. 249

great outbreaks of the epidemic, cases may be met
with of people attacked with boils, not fatal, but
resembling those of the deadly plague. Is it not pro-
bable that these boils contain an attenuated virus of
the plague, and that the passage of this virus into ex-
hausted bodies, which abound only too freely in periods
of famine, may restore to it a greater virulence ?

' The same may be the case with other maladies
which appear suddenly, like typhus in armies and in
camps. Without doubt, the germs which are the
authors of these diseases are everywhere scattered
around, but attenuated ; and in this state a man
may carry them about him or in his intestinal canal
without great damage. They only become dangerous
when, by conditions of overcrowding, and perhaps of
successive developments on the surfaces of wounds, in
bodies enfeebled by disease, their virulence is rein-
forced.'

250 LOUIS PASTEUK.

ETIOLOGY OF SPLENIC FEVER.

M. PASTEUR had triumphed over splenic fever with as
much rigour as precision. But he considered that he
had still to make one further investigation. He had
established the effects of the pest ; he had discovered a
preventive method with which to combat it : he now
wished to know the origin of the evil. Whence comes
splenic fever ? Why is it endemic in certain depart-
ments of France, in certain parts of Kussia, Germany,
Austria, Italy, Spain, and America ? How is it sus-
tained ? It was for a long time believed that splenic
fever was born spontaneously under the influence of
various accidental causes. M. Bouley has related, in
his learned work on the ' Progress of Medicine by
Experimentation,' that in 1842 the Minister of Agri-
culture, M. Cunin-Gridaine, at the request of the
deputies of the departments that were ravaged by the
epidemic, entrusted to M. Delafond, a professor of the
school at Alfort, the task of investigating this malady,
commonly called the ' blood disease,' in the districts in
which it was raging. He was to search out its causes,,

ETIOLOGY OF SPLENIC FEVEK. 251

and ascertain whether they did not result from the-
system of cultivation prevalent in the country.

M. Delafond arrived in Beauce. One fact struck
him — namely, that almost all the animals attacked by
the disease were young, fine, and vigorous : those, in
short, that gave the best promise. Viewing the rich-
ness of the soil and the abundance and quality of the
crops in conjunction with this observation, Delafond
at once elaborated a speculative theory. ' The blood
disease,' said he, ' is nothing but an overfulness — an
excess of blood circulating in the vessels, and especially
the predominance in that liquid of red globules.'

Starting from this idea, his one object was, by
means of logical deduction, to trace everything to this
fundamental error. He analysed the soil, and demon-
strated to what extent it was fitted to furnish crops
that were rich and abounding in nutritive properties.
He analysed the plants. He then complacently re-
ferred the richness of blood of the Beauce sheep to
the richness in nitrogenous principles of the substances
on which they were fed. He examined the lesions of
the diseased animals, and concluded that they were
the consequence of the blood containing too large
a proportion of the organic elements, called globules,
fibrine, albumen, and too small a proportion of water.

' Eeduce the proportion of nutritious elements,' he
wrote as his advice to the agriculturists, 'mix roots
with all that is too rich in nitrogenous principles, and

252 LOUIS PASTEUR.

you will reduce in proportion the losses caused by the
excess of the ultra-nutritious substances with which
you supersaturate your cattle.'

' Such is the very logical conclusion to which Dela-
fond was led,' adds M. Bouley, ridiculing these obser-
vations, based on a method of reasoning, instead of on
the experimental method. * And as a fresh proof of his
theory he mentions the fact that the disease decreases
as you descend the country towards the Loire. On
the right bank of that river — in Sologne, for instance,
which is a low, sandy, damp district — blood disease is
unknown. In the arrondissements of Gien and Mont-
argis and in parts of those of Orleans and Pithiviers
it prevails but little. There, Delafond imperturbably
remarks, the soil is sandy and the herbage not nearly
so rich as in the Beauce plateau ; and there the blood
disease is consequently less common.'

When we consider that such opinions could be
written unchallenged only forty years ago, that they
could even borrow a scientific character from the in-
spiration that gave them birth, we can see the pro-
gress that has since been made, and can realise how
great were the obscurity and uncertainty which have
been dispelled by the experimental method.

The presence of a parasite having been brought to
public notice in the blood of animals suffering from
splenic fever, at the very time when Pasteur had
•shaken the belief in spontaneous generation, people

ETIOLOGY OF SPLENIC FEVER. 25$

grew accustomed to the idea that the stricken animala
might have contracted the germs of the malady from
the outer world, without any spontaneous birth,
strictly so called, of the disease. This opinion was-
strengthened by a knowledge of the spores of the splenic
bacillus. Pasteur, aided by Messieurs Chamberland
and Koux, commenced experiments with a view to
solving this difficult etiological question. The first
experiments took place in the fields of a farm at the
village of St. Germain, near Chartres. Several groups
of sheep were fed on lucern grass which had been
sprinkled with artificially-reared splenic fever bacteria,
or with their germs or spores. Although all the sheep
of the same group absorbed an immense number of
the spores of the parasite, many survived, even after
being visibly affected. Those that died showed all the
symptoms of what is called spontaneous splenic fever.
The period of incubation lasted as long as eight or ten
days, although, in its latter stages, the disease exhibited
those startling features which have caused a belief
that the incubating period is a very short one— short,
that is to say, for those conditions of contagion where
the parasite is not deposited in its pure state under
the animal's skin.

But if prickly plants (notably the pointed ends of
dried thistle leaves, or beards of barley blades cut
into little bits about a centimeter in length) were
added to this infected food, the mortality increased ta

•254 LOUIS PASTEUR.

ti striking extent. On examination after death, the
lesions of these animals were found to be similar to
those observed in sheep which were attacked by splenic
fever in sheds, or which died of the disease in the
open fields.

From that time forward, the idea which had been
predominant in the minds of Pasteur and his fellow-
workers during all their inquiries, was materially
strengthened. They were convinced that the animals
which died of blood disease in the department of Eure
€t Loire had been infected by germs or spores of the
splenic microbe contained in their food ; but the
question remained, Whence came these germs ?

From the moment when all belief in the spon-
taneous generation of the parasite is rejected, attention
is naturally drawn to the possible consequences which
may arise from burying in the earth animals which
have died of splenic fever. In the greater number of
cases, when the knacker's establishment is too far off
and the dead animal is of little value, a trench is dug
on the spot, at a depth varying from half a meter to a
meter. If the animal dies in a field, it is buried where
it falls ; if it dies in a shed the body is carried into a
neighbouring field. There it is buried, and putrefac-
tion sets in ; and since all the splenic fever filaments
of the blood are destroyed by putrefaction, it was
thought that no dissemination of the germs of splenic
fever, after the animal had been buried, could occur.

ETIOLOGY OF SPLENIC FEVER. 255

Pasteur showed that this opinion rested on a super-
ficial observation. Even when the animal is not cut
up, blood spreads itself outside of the body in more or
less abundance. Is it not an habitual characteristic of
the disease, that at the time of death blood issues from
the nostrils and the mouth, and that the urine is often
bloody? All around the corpse, therefore, the earth
is polluted with blood. Moreover it takes several
days for the splenic fever microbe to resolve itself into
harmless granulations by the action of gases, other
than oxygen, which putrefaction generates. During
this time, the excessive inflation of the dead body
causes the liquids of the interior to issue from all the
natural apertures. How often also, a rent in the skin
or the tissues increases this flow. The blood and other
matters, mixed with the surrounding aerated soil, are
no longer in the conditions of putrefaction, but rather
in those which form a suitable medium of cultivation
for the microbe. Experiments confirmed these views.
Adding some splenic fever blood to earth sprinkled
with the water of yeast, or with urine, at summer
temperature, or at the temperature which the fer-
mentation of a dead body keeps up around it, as in a
dung heap, in less than twenty-four hours the splenic
fever filaments deposited with the blood had multiplied
and resolved themselves into spores. These spores
were afterwards found in their state of latent life,
ready to germinate and to communicate splenic fever,

256 LOUIS PASTEUE.

after remaining in the earth for months, and even
years.

These experiments, curious as they were, were
only, so to speak, laboratory experiments. It was
necessary to investigate what happened in the open
country with all the variations of dryness, of damp, and
of cultivation. A happy inspiration came to Pasteur
and his assistants. They had buried in the midst of
summer, in an isolated corner of the farm of St. Ger-
main, near Chartres, a sheep which had died of natural
splenic fever, and of which they had made the autopsy.
Ten months afterwards, and again fourteen months
afterwards, the idea occurred to them of collecting
some of the' earth from this grave. After having ex-
amined it, and established the presence of the spores
of the microbe, they produced, by the inoculation of
guinea-pigs, the splenic disease and death. But the
circumstance which deserves the greatest attention, is
that the same experiment was successfully made with
the earth on the surface of the grave, though this earth
had not been disturbed during the interval. Some
experiments were afterwards made on the earth of
some trenches dug in a meadow of the Jura, where
some cows which had died of splenic fever had been
buried at a depth of two meters. Two years after-
wards, by successive washings of the earth on the sur-
face of the graves, deposits were extracted which at
once produced splenic disease. At three trials within

ETIOLOGY OF SPLENIC FEVER. 257

these two years the same surface earths produced
splenic fever, while, away from the graves, the earth
exhibited nothing of the kind. Finally, Pasteur and
his assistants proved that on the surface of the earth
which covered the buried animals, the germs were again
found, after all the operations of ploughing, sowing,
and reaping.

But how, it will be asked, can the earth, which is
so powerful a filter, allow the germs of microscopic
organisms to rise again to its surface ? Is one not
tempted here to quote Pasteur against himself, since,
in his joint researches with M. Joubert, Pasteur had
proved that the waters of springs issuing from the
earth, even at a shallow depth, are entirely free from
germs ? Such waters, nevertheless, being supplied
from the earth's surface, which is constantly washed
by rain, the effect must be to carry down the finest
particles to the springs. But these latter, notwith-
standing conditions so conducive to their pollution,
remain perfectly pure. Can there be a better proof
that earth of a certain thickness will arrest all solid par-
ticles, even the most minute ? Nevertheless, in these
experiments on splenic fever, we hear of microscopic
germs, starting from the depths and coming up to the
surface — that is to say, in a direction contrary to the
flow of the rain. This is an enigma.

The explanation will cause surprise. The earth-
worms transport the germs, and bring up, from the

s

258 LOUIS PASTEUK.

depths where they lie buried, the terrible microbes. In.
the tiny cylinders of earth which the worms deposit on
the surface of the soil, after the dews of the morning
or after rain, the splenic germs are to be found. It is
easy to prove this directly. If in earth, with which
spores of the microbe have been previously mingled,
we place some worms, and at the end of several days
open the bodies of these worms, with all necessary
precautions, so as to extract from them the earthy
matter which fills their intestinal canals, we find in
them large numbers of splenic fever spores. It is, then,
absolutely proved, that if splenic fever germs exist, as
they often do, in the light earth which covers the pits
in which animals dead of that disease lie buried, these
germs result from the disintegration by rain of the
little excremental cylinders deposited by the earth
worms. The dust of this disintegrated earth spreads
•itself over the grasses on a level with the soil, and
thus it is that animals come to find on the pasture-field,
and in particular kinds of forage, the germs of splenic
fever by which they are infected.

* In these results,' said Pasteur a short time ago at
the Academy of Medicine, ' what outlooks are opened
to the mind in regard to the possible influence of
earths in the etiology of diseases, and the possible
danger of the earth of cemeteries ! '

The earth-worms also bring to the surface other
germs, which, while they are as harmless to the

ETIOLOGY OF SPLENIC FEVER. 259

worms as the splenic germs, are nevertheless bearers
of diseases to which animals are liable. All sorts of
germs are found in them, and the germs of splenic
fever are in fact always associated with those of putre-
faction and septicaemia.

' And now,' concluded Pasteur, when laying before
the Academy a rapid survey of the etiology of splenic
fever, ' is not the remedy naturally indicated ? We
should never bury animals in fields destined either
for cultivation, for forage, or for sheep pasture.
When it is possible a sandy soil should be chosen for
the purpose, or any poor calcareous soil, dry, and
easily desiccated — in a word, soil not suited to the ex-
istence of earth-worms.' M. Tisserand, Director of
Agriculture, has remarked that splenic fever is un-
known in the region of the Savarts of Champagne,
although it is surrounded by countries invaded by the
disease. If the conditions of commerce introduce
splenic fever, it is but a passing accident. Must not
this be attributed to the fact that in these poor soils,
such as that of the camp at Chalons, where the thick-
ness of arable soil is only from 4 to 5 inches, superposed
upon chalk, the worms cannot live ? In such a soil
the burial of a splenic fever animal will give rise
to great quantities of germs, which, owing to the
absence of earth-worms, will abide in the depths of the
soil and remain harmless. Finally, it has been

a 2

260 LOUIS PASTEUK.

proved that the countries subject to splenic fever have-
an argillaceous -calcareous soil, and that the disease is-
unknown in schistose and granitic soils. The contrast
of the results, in relation to such differences of soil, is
seen sometimes in the Department of the Aveyron,
between the right and left side of one and the same
road or watercourse.

May we not now in all confidence assert that, if
the cultivators choose, splenic fever may soon be a
thing of the past among their animals, their shep-
herds, and among the butchers and the tanners of
the towns, because splenic fever and malignant pus-
tule are never spontaneous ? The disease exists only
where it has been sown, or where it has been diffused
by the unconscious instrumentality of the earth-worm.

The progress of vaccination will also contribute to
the disappearance of splenic fever ; for this preventive,
if extensively used, as there is no doubt it will be, must
end by establishing a race of domestic animals which,
having all sprung from vaccinated parents, will in conse-
quence be more resistent to the disease in its worst form.
It will be with them in relation to splenic fever as it
is with ourselves in relation to small-pox. It is a well-
known fact that the ravages of small-pox are much
less considerable in our days than when it first
appeared in Europe. It is difficult not to attribute
this, at least in part, to the prevalence of vaccination.

In the populations where small-pox is introduced

ETIOLOGY OF SPLENIC FEVER. 261

for the first time it has an exceptional intensity.
Some months ago a significant fact of this nature
occurred in Paris. A whole family of Esquimaux
perished from small-pox in the * Jardin d'Acclimata-
tion.' They had never been vaccinated, nor had their
ancestors. They were new to the attacks of small-pox,
which did not spread beyond them.

262 LOUIS PASTEUE.

METHOD OF DISCUSSION AND
CONTRADICTIONS.

EVEKY new discovery produces a revolution in general
ideas ; a revolution gladly hailed by some, but opposed
by others as disturbing their habits of thought and
reasoning. Those also who are thrown out in their
calculations, while engaged in working out a problem
in any way similar to the one that has been solved,,
too often atone for their dilatoriness by furious denial
of the newly asserted truth. The great fact of the
attenuation of virus, the artificial production of the
vaccines of chicken cholera and of splenic fever, the
importance of their employment for the preservation
of animals from these diseases, excited throughout
the world a surprise and enthusiasm which passionate
critics soon sought to disparage. The fiercest attack
was from Germany. It commenced immediately after
Pasteur's triumph at the International Congress of
Medicine held in London in 1881. The German
doctor Koch and his colleagues, MM. Gaffki and

METHOD OF DISCUSSION AND CONTRADICTIONS. 263

Lceffler, published in Berlin, in the report of the
German Sanitary Office, a kind of scientific tirade
against the discovery of virus vaccine, and the possi-
bility of utilising it in the large operations of cattle-
breeding.

At the London Congress Dr. Koch had said to
a French physician that the possibility of attenuating
virus was a thing too good to be true. The whole
question was therefore reopened by Dr. Koch and his
disciples. At first Pasteur let the torrent flow ; but,
not being the man to give way before an adversary,
he at last declared that the attacks of the German
savants must be repelled at Berlin itself. Continual
applications for splenic vaccine were made to him from
different parts of Germany. M. Pasteur replied that,
seeing that the discovery was so formally contested in
Prussia, it would be well, before sending any vaccine
abroad, to institute a great demonstrative experiment,
as had been done at Pouilly-le-Fort.

Dr. Eoloff, head of the Veterinary School of Berlin,
hastened to take the initiative, by an application to
the German Minister of Agriculture. The minister at
once nominated a Commission to follow the experi-
ments in vaccination and to draw up a report for the
German Government. M. Pasteur entrusted the
conduct of the vaccinations to his new colleague, Louis
Thuillier, who accepted with deep and silent joy the
management of an experiment that was to test a

264 LOUIS PASTEUK.

French discovery. He was always ready for anything,
this brave Thuillier, who was destined to die, a martyr
to the cause of science, in the full promise of his youth,
and in the full hope of glory. His courage and his
work were alike great and silent. In the laboratory
he would spend days, even weeks, without speaking,
bent over his microscope with tenacious resolution,
endeavouring to follow Pasteur in all his investigations :
proud to live near his illustrious master, happy to be
his disciple and to be loved by him almost as a son.
What a vacancy he has left in the laboratory ! What
a place he might have held in science !

The composition of the German Commission, over
which M. Beyer, member of the Superior Council of
Government, presided, showed clearly the importance
attached by Germany to the investigation of this
French discovery. Among its members was the
famous Professor Virchow.

The experiments were carried out on the estate
of Pakisch. The minutes and reports of the Com-
mission left no doubt as to the correctness of the facts
announced by Pasteur. But, as the negations of Dr. .
Koch and his colleagues embraced questions beyond
that of the prophylaxy of splenic fever, Pasteur did
not rest content with this initial success ; he sought
for a fresh opportunity of convincing his opponents.
This opportunity occurred in September 1882, when
an International Hygienic Congress was held at

METHOD OF DISCUSSION AND CONTRADICTIONS. 265

Geneva. Thither went Pasteur, hoping to meet Dr.
Koch at the sittings ; and he was not disappointed.
Dr. Koch was there, surrounded by his disciples.
From the tribune of the Congress, Pasteur refuted his
criticism, exposed his errors, and challenged him to
a discussion in the presence of competent judges.
There was an instantaneous salvo of applause, and
everyone awaited Dr. Koch's reply. But he declined
all debate, reserving his case for careful and deliberate
statement in the press.

It took three months for Dr. Koch to bring out a
small pamphlet, and these three months had borne
their fruit. The discovery of the attenuation of virus,
which had been so vehemently attacked only a year
before in the report of the Sanitary Office, was now
extolled by Dr. Koch as a discovery of the first im-
portance. Being, however, unwilling absolutely to
stultify himself, he continued the attack by denying
its efficacy in practical agriculture.

The clear, direct style of argument, which goes
straight to its point, was invariably adopted by
Pasteur.

' Contradictions may retard, although they cannot
ultimately prevent, the recognition of truth,' he once
remarked to me when walking in the gardens of the
Ecole Normale ; ' that is why it is so important to
remove the obstacles which temporarily clog and

266 LOUIS PASTEUK.

hamper it. In scientific discussions, it is not as in
politics,' he added with a smile, ' where demonstration
is often difficult. In the natural sciences, doctrines
must be based on an assemblage of results, of ob-
servations, and of experiments. If a doctrine is
challenged, it seldom happens that its truth or
falsehood cannot be established by the application
of some crucial test. Even a single experiment
will often suffice either to refute or consolidate the
doctrine.'

Eeviewing the labours of the past forty years,
Pasteur then called to mind the numerous controver-
sies in which he had been engaged. Not only had he
been attacked by Pouchet and Joly on the question of
spontaneous generation, by Liebig on the subject of
- /fermentation, by Germans and Italians regarding the
/ attenuation of virus, but every one of his assertions
had been met with such passionate opposition that,
from sheer weariness, he had invariably ended by
referring the matter to some authorised commission,
only asking it to put an end to all strife by coming to
some definite decision.

The upshot was at times somewhat amusing. For
instance, when Pasteur described to the Academy of
Medicine how, simply by lowering the temperature of
a hen, he had made her susceptible to inoculation with
splenic fever, the facts were at once denied by M.
Colin, a professor of the school of Alfort. Pasteur

METHOD OF DISCUSSION AND CONTRADICTIONS. 267

immediately requested that a commission might be
named, which should include both himself and his
opponent among its members. This was on a Tuesday,
one of the Academy days of sitting. The following
Saturday, in presence of the whole commission,
Pasteur produced four hens that had died of splenic
fever. M. Colin himself conducted the autopsy. It
was clear to everyone that their blood was full of the
filaments of the splenic fever parasite. The proces-
verbal was drawn up and signed by all the members
of the commission, necessarily including M. Colin. The
following Tuesday it was read at the sitting of the
Academy. To cover his retreat M. Colin now contended
that the hens had taken splenic fever not because they
had been subjected to a chilling process, but because,
so as to keep them in the water, the poor creatures
had had their wings and feet tied to planks. This
sentimental objection was disposed of by comparative
experiments that had been made on hens similarly
tied and inoculated, but not chilled. The latter had
in no case taken the disease.

At the Academy of Sciences, some days later, a mine
was sprung upon Pasteur by a posthumous publica-
tion of Claude Bernard's. He again submitted this
abruptly raised question to the decision of the
Academy. A series of experiments had been found
among Bernard's papers, having as their object the
inauguration of a new method of spontaneously gene-

268 LOUIS PASTEUE.

rating the substance which causes the fermentation of
the must of the grape.

' I will start for the Jura,' said Pasteur. ' In the
midst of my vineyard, which/ he proudly added, 'is
ten meters square, I will cover over some stocks with
an improvised frame. These stocks will go on living
and bearing grapes, which will ripen. It is now July.
At this time of year, as I have already declared, the
germs of the cellules which form the ferment of the
grape in the vats do not yet exist, either on the green
grapes, on the bunches, or on the vine leaves. I will
envelop the bunches of the stocks that are under-
neath the frame with a layer of cotton wool that has
been raised to a temperature of 150 degrees Centigrade.
This done, I will come back to Paris with the keys of
the frame in my pocket, not returning to the Jura until
the vintage season, at the beginning of October. I
predict to the Academy, that the grapes wrapped in
cotton wool under the frame, and which will have
.grown ripe, may be crushed in the open air, and that
the juice coming from them will not be capable of
fermentation.'

This prediction was fulfilled. In October, Pasteur
returned to the Jura, plucked off several of these
stocks, laden with ripe bunches, and brought them
with the utmost care to Paris. He had at last the
satisfaction of depositing them intact on the table of
the Academy of Sciences. He then invited M. Berthe-

METHOD OF DISCUSSION AND CONTEADICTIONS. 26 £

lot (editor of Bernard's pamphlet), and all his col-
leagues, to cut off as many bunches as they pleased.
' Only crush them in contact with pure air,' said he,.
' and I defy you to produce fermentation.'

How often was Pasteur obliged to return to facts
already proved, not only at the Academy of Sciences,
but at the Academy of Medicine, where M. Jules
Guerin, at the age of eighty, challenged him to a duel
as his scientific ultimatum ! If M. Pasteur at times
pleaded his cause with too much passion, it was the
passion of truth, the burning desire to convince, which
lent such power and defiance to his vibrating voice.
He could not endure his work to be attacked — not
from pride, none was more modest than he — but from
irritation at the denial of positive facts; facts of
which he was a thousand times assured, and which
all the world might verify. No one now remembers
these discussions. Time has passed, and opposition
has been overthrown. It has been granted to Pasteur
to see, everywhere around him, the beneficent results
of his discoveries. From all parts, from his own as
well as from foreign countries, such proofs of admira-
tion and gratitude have been showered upon him as are
usually granted only to those whose death has atoned
for their genius. He has opened up such sources of
wealth to industry and agriculture that, as the learned
English professor Htfxley has truly said, ' Pasteur's
discoveries suffice, of themselves, to cover the war

•270 LOUIS PASTEUR.

indemnity of five milliards of francs paid by France to
Germany.' His investigations of contagious diseases
have revealed immense possibilities in prophylaxy.
But Pasteur considered these marvellous discoveries
as a mere beginning. 'You will see,' he often said,
' how it will all grow by-and-by. Would that my
.time were longer ] '

271

THE LABORATORY OF THE ECOLE
NORMALE.

VABIOUS STUDIES. HYDROPHOBIA.

SINCE the day when a minister told Pasteur, that
there were not 1,500 francs in the budget to allow
for the expenses of his laboratory, science has ob-
tained a little more consideration. At the present
time she has nothing to complain of : her sovereignty
is recognised ; her schools are becoming palaces ;
she has an amply sufficient civil list : she is rich
enough, in short, to pay for her researches. M.
Pasteur's laboratory has had its full share of the
well-bestowed generosity of the State. The municipal
council of Paris even wished to attach vast depen-
dencies to this laboratory. The old garden of the
ancient College Kollin was placed at the disposal of
Pasteur ; who at once hastened to build stables for
lodging horses attacked by glanders, stalls for shelter-
ing splenic fever sheep, and kennels for the reception
of mad dogs. But, while taking advantage of these
hospitable premises, Pasteur still retained, in the

272 LOUIS PASTEUK.

basement of his laboratory in the Eue d'Ulm, a whole
population of animals under experiment. Isolated in
round cages which impart some sense of security, are
the rabid dogs ; some attacked with furious madness,
biting their bars, devouring hay, uttering doleful
howls which those who have once heard can never
forget ; others carrying the germ of this terrible
disease, still fawning with a humble look of tenderness,
as if imploring attention. Hens and chickens pass
their heads through the wooden bars of their coops.
From time to time a cock from the bottom of his den
crows ' a gloomy dawn.' Babbits eat peaceably, while
little families of guinea-pigs cluster together, and at
the least alarm utter a frightened cry. All these
animals are destined to be shortly inoculated. Each
morning a round of inspection is made in this little
hospital of condemned animals. The dead are taken
out, carried to one of the upper rooms, and placed on
the dissecting-boards.

It is also to such boards that living animals are
fastened "when it is necessary to experiment upon
them. Certainly when one sees a dog lying with a
forlorn look, its feet tied, its body trembling from
fright, on the point of undergoing, though in full
health, a bloody operation, one cannot suppress the
feelings of pity. But a single visit to a physiological
laboratory suffices to reveal vivisection in its only

THE LABORATORY OF THE ECOLE NORM ALE. 273

and true light ; that of the interest it offers to science,
and the results it may have in store for the benefit of
humanity. Moreover, in Pasteur's laboratory, every
dog subjected to vivisection is chloroformed. The per-
sons who take up the controversy about vivisection are
careful that the outside world shall see only the suffer-
ing and anguish of the animal, where the solution of a
problem should be the object kept in view. Would the
English physiologist Harvey have discovered the cir-
culation of the blood, if he had not practised vivisection
on deer in the park of Charles I. ? Would Claude
Bernard have been able, without vivisection, to demon-
strate the glycogenic function of the liver ? If Pasteur
had not sacrificed some fowls and sheep, would
the great scientific fact of the attenuation of virus
have been discovered? If 500 dogs had to perish,
what would that be, compared with the discovery to-
morrow of the cause of hydrophobia, and of the
means of protecting humanity against this frightful
scourge ?

On one occasion, in presence of a large assembly,
Pasteur made an experiment on atmospheric oxygen.
He placed under a glass bell a bird, which in a short
time, after having consumed the oxygen contained
in the bell, gathered itself up into a ball, opened its
beak, and shut its eyes, as if it were going to die.
At this moment Pasteur introduced a second sparrow,
which, passing directly from the ordinary air into

T

274 LOUIS PASTEUR.

the bell, without any gradual preparation, immedi-
ately fell, asphyxiated. There was a little exclamation
of horror and a movement of pity in the audience.
While the first sparrow, which had gone through
the ordeal unharmed, was set free, and gradually
revived, Pasteur turned towards the assembly and
said —

' I never had the courage to kill a bird in sport,
but when it is a question of experiment I am deterred
by no scruple. Science has the right to assert the
sovereignty of its aims.'

But to return to the animals of the laboratory :
From the little white mice, which hide themselves in a
packet of wadding, to the dogs which bark furiously
in their iron cages, all are devoted to death. But it
is not only the inmates of the laboratory which daily
succeed each other upon the operating and dissecting
tables. From divers parts of France, hampers full of
fowls which have died of cholera, or of some other
disease, are sent to Pasteur. Here is an enormous
basket packed with straw containing the dead body
of a pig which had died of measles. This fragment
of lung, packed in a tin box, belonged to a cow which
died of peripneumonia. Other packets are still more
precious. Since Pasteur went to Pauillac two years
ago, to watch for the return of a ship which was to
bring back some passengers attacked with yellow

THE LABOKATOKY OF THE ECOLE NORMALE. 275

fever, he sometimes receives from a distant country a
bottled dose of vomito negro.

Everywhere, on the work tables, are to be seen tubes
filled with blood, microscope slides carrying little drops.
In the stoves are ranged the cultivating flasks, which
resemble little flasks of liqueur. The point of a needle
dipped into one of these flasks is sufficient to cause
death. Enclosed in their glass prison, millions upon
millions of microbes live and multiply.

It is really a curious spectacle this workshop of
research and discovery. How numerous and varied
are the subjects which are being studied, and with
what energy and patience does Pasteur attack them !
It is not only to the most dreaded diseases that he has
applied the germ theory. He has extended it to certain
common disorders. Everything to him is a subject
for experiment. In May 1879, a person who was
working in the laboratory was troubled with boils,
which reappeared, as usually happens, at short in-
tervals, sometimes on one part of the body, sometimes
on another. Pasteur, whose mind was constantly
dwelling on the part played by microscopic organisms,
asked himself if the pus of the boils did not contain
a parasite, the presence and development of which,
and its accidental transport here and there in the
body, might be the cause of the [local inflammation
and of the formation of the pus. The constant re-
appearance of the evil would be thus accounted for.

T 2

276 LOUIS PASTEUK.

The pus of the first boil, which was situated on the
nape of the neck, was collected in great purity ; some
days afterwards, the pus of a second boil, then of a
third boil, was collected. The pus, or the blood-
stained lymph of the red swelling which preceded the
formation of the pus, were sown in a sterilised infusion r
and each time a microbe, formed of little spherical
points connected in pairs, frequently united in small
clusters, was seen to develop itself. The cultivating
liquid was sometimes infusion of fowl, sometimes of
yeast. In the infusion of yeast the little grains are
suspended in pairs throughout the liquid, which is-
uniformly thickened with them. In the fowl infu-
sion, the grains are united into little clusters, which
cover the sides of the vessels, the liquid remaining
clear as long as it is not shaken.

New observations were made upon a series of
boils, in the case of a man sent to Pasteur by Dr.
Maurice Eaynaud. The same parasite was again
found — a unique parasite, distinct from all others. At
the Hospital Lariboisiere, a woman whose back was.
covered with boils, offered another opportunity for ex-
periment, and with the same result. It appears cer-
tain, then, that every boil contains a microscopic
aerobic microbe, and that to it are due the local in-
flammation and the consequent formation of pus.

. When guinea-pigs or rabbits are inoculated with the
cultivating liquids, little abscesses are formed, which,.

THE LABOKATOKY OF THE ECOLE NORMALE. 277

however, quickly disappear. As long as the cure of
these little abscesses is not quite completed, one can ex-
tract from them the microscopic organism which has
formed them. When the little parasite is sought for in
the general blood of those attacked with boils it is not
found. The cause of this, no doubt, is that an aerobic
parasite has always some difficulty in developing itself
in the blood. The blood corpuscles appropriate, and
do not willingly give up to a foreign organism, the
oxygen which they require. There is a struggle for
life, and in the struggle against the boils the victory
is not doubtful. It might be thought, then, that the
little organism of boils does not exist in the blood, but
there is no doubt that if, instead of a small drop of
blood, one could put several grammes or more into
cultivation fruitful results would follow. The little
parasite is no doubt conveyed by the blood at one time
or other. It is transported from a boil, in the process
of development, to another point of the body, where it
may be fortuitously arrested, there to cultivate itself
and form a new boil.

' It is to be wished,' said Pasteur, ' that a patient
would submit to a number of punctures on different
parts of the body, distant from boils already formed
or in process of formation, and that with the blood
thus taken from the general circulation a multitude of
cultivations might be carried on. I am persuaded,'
he added, * that, among these cultivations, we should

278 LOUIS PASTEUE.

find some fruitful in the little organism of the

•y. boils.'

But whilst Dr. Maurice Baynaud gave Pasteur the
means of studying boils, Dr. Lannelongue enabled him
to investigate that serious disease of the bones and

^ marrow called ' osteomyelitis.' In February 1880
that skilful surgeon, who has published a highly
esteemed work on osteomyelitis, and on the possi-
bility of its cure by trepanning the bone, followed by
washings and antiseptic dressings, conducted Pasteur
to the Hospice Trousseau. A little girl twelve years
of age, attacked with this cruel malady, was about to
be operated upon. The right knee was much swollen,
as was also all the leg to below the calf, and a part
of the thigh above the knee. After having chloro-
formed the child, Dr. Lannelongue made a long in-
cision below the knee, from which pus flowed
abundantly. The bone of the tibia was laid bare for
a considerable length. Three trepanning perforations
were then made in the bone, from each of which the
pus issued in great quantities. Pasteur carefully
collected, with all the conditions necessary to the pre-
servation of their purity, the pus of the exterior and
the pus of the interior of the bone, and, returning to
his laboratory, he examined them attentively. The
direct observation, by a microscope, of the two speci-
mens of pus was extremely interesting. It was obvious
that they contained, in large quantities, an organism.

THE LABOEATORY OF THE ECOLE NOEMALE. 279

like that of boils, in pairs of two or four, and also in
parcels, some with a clearly denned outline, others
scarcely visible, and with very faint outlines. The
external pus showed an abundance of pus globules,
but that of the interior did not show any. It was
like a paste entirely composed of microbes, so numerous
and fertile that, in less than six hours after sowing them
in the cultivating liquid, the development of the little
microbe had commenced, and was rendered visible to
the naked eye by a slight but general turbidity of the
liquid.

Its close resemblance to the organism of the boil
might lead to the assertion that they are identical, if
it were not known how great are the physiological
differences that may exist between microscopic parasites
of the same appearance and the same dimensions.

As Pasteur advanced in these studies, he found at
the Academy of Medicine some fellow labourers, who
being keenly interested in such researches did all they
could to promote them. Thus M. Villemin, the chief
medical officer of the Val de Grace (who had with so
much sagacity discovered the contagion of tuber-
culosis) when typhoid fever was raging in Paris two
years ago, never allowed a case of the fever to pass
through his hands without informing Pasteur, who

280 LOUIS PASTEUR.

habitually went himself to collect specimens of the
blood of those who had died. How numerous were the
drops of blood thus enclosed in little tubes, and how
frequent the attempts at cultivation, as yet without re-
sult, in the hope of finding the cause of a disease which
claims so many victims ! There is another malady to
which Dr. Hervieux especially called Pasteur's atten-
tion, and by which so many women are attacked —
/ puerperal fever. He went with M. Hervieux to the
Maternity Hospital, to visit a woman under his charge
who had contracted puerperal fever some days after her
confinement. By means of a pin a prick was made in
the forefinger of the left hand, which had been washed
previously with dilute alcohol and carbolic acid, and
dried with singed linen. The drop of blood taken
in this way was sown in an infusion of fowl. For
some days the cultivation remained sterile. Next
day blood was taken from a fresh puncture, and
this time it proved fertile. The woman died three
days after. The blood, therefore, already at the time
when Pasteur had taken it, three days at least before
death, contained a microscopic parasite capable of
cultivation. Eighteen hours before this woman died,
some blood taken from the left foot had been sown,
and, like the former, it had proved productive ; but
— and this fact deserves to be noted — while the first
productive cultivation only contained a microbe re-
sembling that of boils, the other cultivation contained

THE LABORATORY OF THE ECOLE NORMALE. 281

long flexible chaplets clustered together like tangled
strings of beads.

At the post-mortem examination of this woman
large quantities of pus were found in the peritoneum
and the uterus. This pus was sown with all due pre-
caution. Some blood taken from the basilic and
femoral veins was likewise sown. It was everywhere
easy to recognise the long chaplets in little tangled
parcels, and always without admixture of other
organisms, except in the cultivation of the perito-
neal pus, which, besides the long strings of grains,
showed also the little pyogenic vibrios to which Pasteur
had already assigned the name of the pus^organism.

From the Maternity Hospital Pasteur went to the
Hopital Lariboisiere, where he had been informed
that another woman had just died of the same fever.
From a puncture in the peritoneum he collected some
pus which was found there in great abundance. He
sowed this, as well as some blood taken from a vein in
the arm. The culture of the pus furnished the long
strings of grains and the little pyogenic vibrio. The
culture of the blood exhibited only the long strings
quite pure.

Pasteur made many other observations of the
same kind in cases of puerperal fever. He arrived at
the conclusion that, under the name of puerperal fever,
diseases of different symptoms were classed, but which
rail appear to be the result of the invasion of common

282 LOUIS PASTEUE.

organisms, which develop themselves on the surface of
wounded parts, and from thence spread themselves,
in one form or another, by the medium of the
blood or of the lymphatics, over • different parts of
the body. Here the various morbid symptoms are
determined by the nature of the parasite and the
general constitution of the patient. Pasteur is con-
vinced that, with the possible exception of cases
where, by the presence either of internal or external
abscesses, the body, before confinement, contains
microscopic organisms, the antiseptic treatment ought
to be infallible in preventing puerperal fever from
declaring itself. The employment of carbolic acid
may be of great service ; but its smell, and often the
melancholy association of ideas which it awakens,
might render it unsuitable for women in labour.
There is not the same objection to concentrated
solutions of boric acid, which, M the ordinary tem-
perature, contain from thirty to forty grammes of acid
to one litre of water.

' Would it not be very useful,' said Pasteur one
day, when developing his ideas and observations before
the Academy of Sciences, ' to place always by the bed-
side of each patient the concentrated and warm solu-
tion of boric acid, with compresses to be very fre-
quently renewed, after having been soaked in the
solution, these applications being begun immediately
after the confinement ? It would also be prudent, before

THE LABORATORY OF THE ECOLE NORMALE. 283-

using the compresses, to put them into a hot-air stove,,
at a temperature of 150 degrees, which is more than
sufficient to kill all the germs of common organisms.

1 1 have,' he added, ' represented the facts as they
have appeared to me, and I have hazarded the interpre-
tation of them ; but I do not disguise from myself that,
in the domain of medicine, it is difficult to withdraw
oneself entirely from a pre-existing subjective bias ;
neither do I forget that the medical and veterinary
studies are foreign to myself: therefore I earnestly
desire judgment and criticism. While I am little
tolerant of frivolous contradiction or of prejudice,
despising as I do that vulgar scepticism which would
erect doubt into a system, I honour that militant
scepticism which makes doubt the basis of a method ,
whose motto is " More light."

Since these ideas have penetrated further into
practice ; puerperal fever, I was told lately by a dis-
tinguished medical man, is hardly known in the
Maternity Hospital. The employment of a solution
of one to a thousandth of corrosive sublimate, which
is one of the best antiseptics, gives excellent results,,
and keeps off all danger. May it not be permitted
to hope that puerperal fever will soon disappear
in the same way that purulent infection has disap-
peared in hospitals, since the introduction of Lister's,
dressings ?

284 LOUIS PASTEUE.

II.

In 1882, a new malady occupied the attention of
the laboratory of the Ecole Normale, a malady the
name of which was not even known in Paris, but
which made great ravages in the country — namely,
swine fever (rouget). Here, again, it is a microbe
which causes the disorder. This microbe was first
perceived by Thuillier, in a little commune of the De-
partement de Vienne, when examining the blood and
humours of pigs which had died of the fever. Ex-
periments were at once set on foot in the laboratory,
with the view of proving that the microbe was really
the cause of the disease. The microbe was cultivated
in a sterilised infusion of veal. This cultivation was
passed on to a succeeding one, a small drop of the
preceding cultivation being always taken for seed.
Inoculations from these last cultivations produced the
fever in certain breeds of pigs. The proof was thus
given that the microbe was really the origin of the
disease.

Pasteur then, accompanied by Thuillier and a
young assistant, M. Loir, went, in his turn, to study
the disease in the Department of Yaucluse. He re-
mained more than a month in the canton of Bollene,
in the house of a veterinary surgeon, M. Maucuer,
who took him to all the pigsties in the arrondissement.

THE LABORATORY OF THE ECOLE NORMALE. 285-

After having had recourse to the oxygen of the air ta
attenuate the virulence of the microbe, Pasteur made
some experiments in vaccination. Some pigs which
had been vaccinated remained in the canton of Bol-
lene, under the supervision of M. Maucuer, the
owners having pledged themselves to keep their
vaccinated pigs for at least a year. In the ensuing
September, when swine fever raged everywhere in the
canton of Bollene and in the arrondissement of Orange,
not a single vaccinated pig was attacked. ' They are all
flourishing,' wrote M. Maucuer. An address of thanks
was sent to Pasteur by the municipal council of
Bollene.

But, notwithstanding these happy results, the-
question of the application of vaccines to different
breeds requires still further investigation, before the
vaccination of pigs can become general.

Soon afterwards a method, different from that of
the atmospheric oxygen, for weakening the virulence of
the fever virus, was tried in the laboratory.

Pasteur had proved that viruses are not morbid
entities, that they can assume numerous forms, and
especially physiological properties, dependent on the
medium in which they live and multiply. The viru-
lence belongs to living microscopic species, but is at
the same time essentially modifiable. It may be
weakened or intensified, and each of these states i&
capable of being made permanent by culture. A

286 LOUIS PASTEUE.

microbe is virulent in an animal, when it has the
power of swarming in the body of that animal, after
the manner of a parasite, and of producing, by the re-
newal of its own life, disturbances which cause disease
and death. If this microbe has lived in any species
of animal — that is to say, if several times over it has
passed from the body of one individual into that of
another of the same kind, without having been sub-
jected to any sensible exterior influence during its
passage — we may consider that the virulence of this
parasite has reached a fixed and maximum state for
the individuals of that race. The splenic fever para-
site pertaining to sheep, for instance, varies little
from one subject to another or from one year to
another in the same country ; this must be attributed,
doubtless, to the fact that, in its successive passages
through the sheep, the habit of the parasite to live in
sheep has, so to speak, attained a definite state. It is
thus with the virus of the Jennerian vaccination. But
the virulence of a virus which is not at its maximum
may be essentially modified by its passage into a
succession of individuals of the same race. It will be
remembered how, when Pasteur and his assistants
wished to increase progressively the virulence of the
virus of chicken cholera and splenic fever, so as to
bring them at last to their maximum intensity, these
viruses were first inoculated into young subjects, and
from them successively into older ones.

THE LABOK4TOEY OF THE ECOLE NOKMALE. 287

' The Academy remembers, without doubt,' said
Pasteur in a recent communication, * that, some time
ago, we discovered a microbe virus in the saliva of
hydrophobia. This microbe, though very virulent for
rabbits, is shown to be harmless for adult guinea-pigs,
but it kills rapidly guinea-pigs only some hours or
days old. In following out this inoculation from
young guinea-pigs, we have seen the virulence increase,
and easily arrive at the point of causing death to
older guinea-pigs. There was even at last a marked
difference in the lesions. The increase of virulence,
by successive passages through individuals of one
race, was clearly shown.

' But the new and unexpected result that I wish to
point out to the Academy consists in this : that the
microbe, after having increased its virulence by
successive passages through the bodies of guinea-pigs,
shows itself to be less virulent in relation to rabbits
than it was before,

' In these new conditions, it gives to the rabbit a
disease which is spontaneously curable ; and, moreover,
having once gone through the malady, the animal be-
comes refractory in regard to the microbe which is
deadly to rabbits. From this arises the all-important
consequence, that the habit of living in one species
(the guinea-pig) at a definite corresponding degree of
virulence, can change this virulence in relation to
another species (the rabbit), so much diminishing its

288 LOUIS PASTEUK.

effects as to cause it to become a vaccine for this latter
species.

' The importance of this result cannot fail to be
perceived by everyone, for it contains the secret of a
new method of attenuation, which can be applied to
some of the most virulent viruses. We will give an
example and an application of it.

' If a pigeon be inoculated in the pectoral muscle
with the microbe of swine fever, the pigeon dies in an
interval of six or eight days, after having shown the-
apparent exterior symptoms of fowl cholera.

' When a second pigeon is inoculated with the blood
of the first, a third with that of the second, and so on
in succession, the microbe acclimatises itself to the
pigeon. The symptoms of forming itself into a ball,
and of somnolence, which are the habitual character-
istics of the disease, appear in a much shorter time
than with the first pigeons of the series. Death
likewise comes on more rapidly. Finally, the blood
of the last pigeons exhibits much more virulence in
the pig than even the most infectious products of
a pig that has died of what is called spontaneous
fever. '

' The passage of the swine fever microbe through
rabbits leads to quite a different result. Eabbits ino-
culated with the infectious products of a pig that has
died of the fever, or with the cultivations of them, are
always made ill and most frequently die.

THE LABORATORY OF THE ECOLE NORMALE. 289

* When the virus is inoculated from rabbit to
rabbit, the microbe acclimatises itself to the rabbit.
All the animals die, and death comes in a very few days.
The cultures of the blood of these rabbits in sterilised
media become progressively easy and more abun-
dant. The microbe itself changes its aspect somewhat,
grows rather larger than in the pig, and appears in
the form of an 8, without the filiform lengthening out
characteristic of certain other cultures.

* When pigs are inoculated with the blood of the
last rabbits, and the results compared with those
obtained from the first of the series, it is found
that the virulence has been progressively diminishing
from the first rabbit to the following ones. Very soon
the blood of the rabbits ceases to cause death in the
pigs, though it renders them ill. On recovery they
are proof against the deadly swine fever.'

III.

But in the midst of these investigations undertaken
by Pasteur, there is one which is paramount over all
the others, one on which for three years all his
efforts, as well as those of his pupils, have been con-
centrated, and this is Hydrophobia. Mysterious in its
incubation, alarming in its symptoms, Pasteur's
attention had for a long time been drawn to it, when
in 1880 he finally attacked it. Besides the attraction

290 LOUIS PASTEUR.

which an obscure problem had for him, he felt that if
he succeeded in discovering the probably microbean
etiology of such a disease, he would carry all minds
with him into the current of these new ideas. He had
been very often struck, if not with the opposition, at
least with the prudent and circumspect reserve, shown
in the examination of his doctrine, by a considerable
number of physicians who, possessed by the idea that
the moral element could cause modifications in the
symptoms and development of a malady in man, are
not disposed to recognise the least assimilation between
human diseases and those of the animal species. No
doubt the emotional qualities, grave family cares, the
terror of approaching death, the dread of the great un-
known, may modify the course of the evil in man, may
aggravate it, even hasten it ; but, whilst recognising —
for never was there a man more a creature of senti-
ment than he — what there is of deep truth in this
opinion, Pasteur could not help thinking that the first
origin, the cause of every contagious malady, is physio-
logically the same in the two groups, and that our
bodies, notwithstanding our superior moral qualities,
are exposed to the same dangers, to the same disorders,
as the bodies of animals.

To overcome these resistances, it was necessary, as
in the great experiments on splenic fever, to attack a
disease common both to men and animals — one in
which experimentation, the only, but great, strength

THE LABOKATORY OF THE ECOLE NOKMALE. 291

of Pasteur, was supreme. Hydrophobia offered these
conditions.

Again, it was Dr. Lannelongue who introduced
Pasteur to his first case of hydrophobia. On
December 10, 1880, a child of five years old, who
had been bitten in the face a month previously, was
dying in the Trousseau Hospital. Devoured at the
time by a raging thirst, and seized with a horror for
all liquids, he approached with his lips the spout of a
closed coffee pot, then suddenly started back — the
throat contracted — a prey to such fury that he insulted
the nursing sister who was attending on him. He was
at the same time attacked by aerophobia to a prodigious
degree. At a certain moment, the heel of one of his
feet protruded from the bed. An assistant blew on it.
The child had not seen the assistant, and the breath
of air was so light as to be almost imperceptible. The
poor child flew into a rage, and a violent spasm
seized him in the throat. The next day delirium
began, a frightful delirium. The frothy matters
whieh filled his throat suffocated him.

Four hours after his death, the mueus from the
palate of the child was collected. It was diluted with
a little water, and two rabbits were inoculated under
the skin of the abdomen. The rabbits perished in
less than thirty-six hours. The saliva of these dead
rabbits also transmitted the disease to fresh rabbits.
Did it not seem as if one had got hold of an inocula-

292 LOUIS PASTEUR.

tion of hydrophobia ? Such was in fact the conclusion
of Dr. Maurice Eaynaud, who, having been informed,
at the same time as Pasteur, of the illness of the child,
had made, on his own account, some experiments on
rabbits. His rabbits were dead. Already a year
previously M. Maurice Eaynaud had announced the
transmission, by the saliva, of rabies from man to
rabbits. ' We are, then, in the presence of a new fact
of this kind,' he said, ' and we really believe, until a
proof to the contrary is given us, that these latter
rabbits died of hydrophobia.'

With his habitual prudence, and trusting more to
the results of experiment than to medical observation
alone, Pasteur was not in a hurry to form such
positive conclusions. He began by doing what Dr.
Maurice Kaynaud had neglected to do. He examined
with the microscope the tissues and the blood of the
rabbits inoculated in the laboratory ; he discovered,
both in those that were dead, and in those which were
on the point of death, the presence of a special
microbe, easily cultivable in a pure state and of
which the successive cultures caused the death of
other rabbits. Invariably, the same microbe appeared
in the blood. As one or two days sufficed to cause
death, hydrophobia could not have had time to make
its appearance. Pasteur, moreover, found this same
microbe in the saliva of children who had died of
common maladies, and even in the normal saliva of

THE LABORATORY OF THE ECOLE NORMALE. 293

healthy adults. It was a new microbe, causing a
disease unknown up to that time. To Pasteur it
seemed, in the case of the experiments made with the
mucus from the child's palate, to be simply an ac-
companiment of the rabic virus.

This microbe of the saliva is very easily cultivated
in sterile infusions — that of veal, for example — and
successive cultures can be made in the usual way.
The virulence continues. Could the virulence be at-
tenuated, asked Pasteur, by the action of the oxygen of
the air ? This would, by a new example, go to esta-
blish the generalisation of the method of attenuation by
oxygen. The attempt succeeded. When care is taken,
as with the attenuation of the fowl cholera contagium,
not to allow more than some hours' interval to elapse
between one cultivation and the succeeding one, the
virulence of the successive cultivations of the microbe
of the saliva is preserved in some sort indefinitely. In
other words, if it be arranged that the cultures succeed
each other every twelve hours, the rabbits inoculated
from the last cultures die as quickly as those inocu-
lated from the first. Thuillier had had the patience
to make, in this manner, eighty cultures in contact
with air, and eighty cultures in a vacuum ; the mi-
crobe of the saliva being both aerobic and anaerobic.
The eightieth culture killed as quickly as the first.
But by allowing the successive cultures to remain for

294 LOUIS PASTEUE.

some time in contact with the air, before passing from
one culture to the following one, the virulence of the
cultures becomes enfeebled. Thus, then, as in fowl
cholera, attenuated cultures of the microbe can be ob-
tained. Unlike what happens with cholera, however,
the cultures of the microbe of the saliva, exposed
to the contact of air, perish very quickly. Two or
three days of keeping suffice for the parent cultivation
to lose all virulence. The seed, taken in any quantity
from it, does not fertilise a new cultivation. But,
before perishing, this culture passes through very differ-
ent degrees of progressively weakened virulence, and
it is easy with these cultivations to render rabbits ill
without causing their death. Once cured, they resist
all inoculation which would be mortal for others.
The oxygen of the air is manifestly the transformer of
this virulent virus into vaccine virus ; for, if the viru-
lent blood or cultivations remain inclosed in their
tubes, sealed from all entrance of the air, they retain
not only for some hours, but for months, their life and
their original virulence.

But though these results were as new as they were
unexpected, and though one cause of confusion in the
study of this terrible problem was removed, yet these
first researches were not marked by any progress in
the etiology of hydrophobia. The question remained
wholly unsolved.

THE LABORATORY OF THE ECOLE NORMALE. 295

Impatient with the length of time required for
the incuhation of the disease, and with the obligation
of waiting whole months for the result of an experi-
ment, when the subject demanded such numerous
ones, Pasteur began to seek some means of producing
hydrophobia with certainty and of making it appear
more rapidly. Notwithstanding the assertion of a
professor of the veterinary school at Lyons that the
saliva of the rabid dog alone contained the virus of
the disease, and that he had failed in every attempt to
inoculate, whether with the substance of the brain or
with the spinal marrow of rabid dogs ; Pasteur, with
due care as to purity, introduced under the skin of
some rabbits and some dogs, divers parts of the brain
of a dog which had died in a rabid state. Hydro-
phobia declared itself in both dogs and rabbits, with a
duration of incubation about equal to that which
followed the ordinary bite of a dog. Although it was
necessary still to submit to this long uncertainty with
regard to the incubation, one great result was obtained :
hydrophobia could be inoculated with other matter
than saliva. Not only is the saliva always impure,
containing a saliva microbe, which is endowed with
a special virulence of its own, but it presents other
inconveniences. It is necessary, in these researches,
to have a supply of material constantly at hand.
Now, the saliva loses its rabic virulence in twenty-
four hours. The existence of the rabic virulence in

296 LOUIS PASTEUE.

the brain substance placed, on the contrary, at the
disposal of the experimenter, an abundance of the
virus, in a state of great purity and capable of long
preservation.

The idea then occurred to Pasteur and his assist-
ants, to inoculate the virulent rabic matter in its pure
state under the dura mater on the surface of the brain
of a dog. Why not carry the virus, said Pasteur,
directly to the place of its activity and development ?
After having trepanned the skull of a chloroformed
dog, a little bit of the medulla of an animal which had
died of hydrophobia was deposited on the surface of
the brain. As soon as the influence of the chloroform
was dissipated, the dog recovered its healthy appear-
ance. It ate its food that same evening. But after
some days the symptoms of hydrophobia appeared.
The animal became dejected and restless ; it tossed
its litter about, refused all nourishment. A doleful,
sharp howling was the first indication of the rabic
voice, which is but one long cry of suffering and
appeal, mingled with barkings from hallucinations.
The stomach became depraved ; the dog swallowed hay
and straw. It soon grew furious, agitated with violent
convulsions ; finally, after a last fit, it died. During
all this time there was great rejoicing in the labora-
tory. They were at last in possession of a method
for singularly shortening the period of incubation, and

THE LABORATORY OF THE ECOLE NORMALE. 297

for communicating the disease with certainty. The
experiments were multiplied ; all the dogs which were
trepanned, and which received on the surface of the
brain a little of the medulla of the rabid animal,
succumbed to the disease, with very rare exceptions,
within a period of twenty days. Did not the method
pursued demonstrate, among other things, that hydro-
phobia is a disease of the brain ; that the seat of the
rabic virus, far from being exclusively in the saliva,
belongs, above all, to the cerebral matter ?

Other results, in addition to this one, were not slow
in revealing themselves. It was established that not
only the brain, but the spinal marrow, along its whole
length, may be rabic, and that the nerves themselves
throughout their whole system, from the centre to the
periphery, may contain the virus of hydrophobia. If
there exists a microbe of hydrophobia, its medium
of cultivation in the body is, par excellence, the brain,
the spinal marrow, and the nerves. It was also
established that there were localisations of virus in
certain parts of the mucous system, and that the very
considerable differences of rabic symptoms which exist
in different cases of hydrophobia, must be sought for
in this fact. At the moment of death the medulla
oblongata is always rabic. Finally, it was established
that hydrophobia could be given (and almost as
rapidly as by trepanning) by inoculating rabic nervous
matter into the circulation of the blood by a vein*

x

293 LOUIS PASTEUR.

In presence of such facts it is easy to account for
what takes place in the case of a bite from a mad dog.
The circulation of the blood carries the virus to the
surface of the brain, or to the surface of the spinal
marrow; there it houses itself in particular spots,
and, little by little, invades the nervous matter.
This last would be progressively attacked throughout,
if death from the medulla oblongata did not almost
always supervene before the propagation of the virus
can become general.

The saliva glands are often rabic, doubtless because
the virus oozes into them, little by little, from the
nerves which enter these glands. Thus may the pre-
sence of this virus be explained in the saliva of mad
dogs, where, at all times since the disease was first
known, it has been found to exist. When the first
point attacked by the virus is the spinal marrow, or
certain portions of it, a general paralysis often pre-
cedes death. In this case the howling and biting
symptoms are for the most part absent, and the dog
continues to be caressing until it dies.

In a thesis written by M. Eoux, Pasteur's labora-
tory assistant, last July, we read the following : — ' If
we examine with care a little of the pulp taken freshly
from the brain of a rabid animal, and compare it with
the same substance from the brain of a healthy
animal, it is difficult to distinguish any difference
between the two. In the rabic pulp, however, besides

THE LABORATORY OF THE ECOLE NORMALS. 299

the granulations which are found in profusion in the
healthy pulp, there seem to exist little grains of ex-
treme minuteness, almost imperceptible even with the
strongest microscopes. In the cephalo-rachidic liquid
so limpid in appearance, it is possible with great
attention to detect similar little grains. Can this be
the microbe of hydrophobia ? Some do not hesitate
to affirm that it is. For ourselves, as long as the
cultivation of the microbe outside of the organism has
not been effected, and that hydrophobia has not been
communicated by means of artificial cultures, we shall
abstain from expressing a definite opinion on the
subject.'

But the grand problem in regard to hydrophobia
is, not so much the isolation of the microbe, as the
finding of a means of preventing this frightful disease.

Even now the experiments are in full swing.
Biting dogs and bitten dogs fill the laboratory. With-
out reckoning the hundreds of mad dogs that have
died in the laboratory during the last three years,
there never occurs a case of hydrophobia in Paris
of which Pasteur is not informed. Not long ago
a veterinary surgeon telegraphed to him, * Attack
at its height in poodle-dog and bull-dog. Come.'
Pasteur invited me to accompany him, and we started,
carrying six rabbits with us in a basket. The
two dogs were rabid to the last degree. The bull dog

300 LOUIS PASTEUR.

especially, an enormous creature, howled and foamed
in its cage. A bar of iron was held out to him : he
threw himself upon it, and there was great difficulty
in drawing it away from his bloody fangs. One of the
rabbits was then brought near to the cage, and its
drooping ear was allowed to pass through the bars.
But, notwithstanding this provocation, the dog flung
himself down at the bottom of his cage and refused to
bite.

Two youths then threw a cord with a slip loop
over the dog, as a lasso is thrown. The animal was
caught and drawn to the edge of the cage. There
they managed to get hold of him and to secure his
jaws ; and the dog, suffocating with fury, his eyes
bloodshot, and his body convulsed with a violent
spasntj was extended upon a table and held motion-
less, while Pasteur, leaning over his foaming head,
at the distance of a finger's length, sucked up into
a narrow tube some drops of the saliva. In the base-
ment of the veterinary surgeon's house, witnessing this
formidable tete-a-tete, I thought Pasteur grander than
I had ever thought him before.

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