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LOUIS PASTEUR 
 
 HIS LIFE A^D LABOURS 
 
 £7 HIS SON-IN-LAW 
 
 TEANSLATED FEOM THE FEEXCH 
 BY 
 
 LADY CLAUD HAMILTON 
 
 With an Introduction 
 
 Bt JOHN TYNDALL 
 
 ]S1EW YORK 
 D. APPLETOK AND COMPANY 
 
 1, 3. AND 5 BOND STREET 
 1886. 
 
//>rv 
 
 V&i wv.o--vv.^iL/ . 
 
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 PKEFACE. 
 
 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 ? What 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.' 
 
PEEFACE. Vii 
 
 * I could not waste my time in going back upon 
 things already accomplished.' 
 
 * 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 
 smUe, 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.' 
 Initiated by affection, I would make myself initiator 
 by admiration. It would be the history of a learned 
 
 ' ' Vernis des maitres.' 
 
Viii PEEFACE. 
 
 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 wUl 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 188a 
 
CONTENTS. 
 
 PAGE 
 
 IITTEOBUCTION, BY PEOFESSOR XTJTDALL . , . . xi 
 
 EECOLLECTIONS OF CHILDHOOD AlfD YOUTH — FIRST DISCOVERIES 1 
 
 FERMENTATION 40 
 
 ACETIC FERMENTATION — THE MANEFACXXTEE OF VINEGAR . 66 
 
 THE QUESTION OF SPONTANEOUS GENERATION . . . . 89 
 
 ETUDIES ON VeiNE 112 
 
 THE SILKWORM-DISEASE 127 
 
 DECISIVE EXPERIMENTS 164 
 
 STUDIES ON BEER 168 
 
 VIRULENT DISEASES — SPLENIC FEVER, SEPTICJLMTA . . 176 
 
 FOWL CHOLERA 212 
 
 ATTENUATED VIRUS, OR VACCINATION — THE FOWL CHOLERA 
 
 VACCINE 220 
 
 THE VACCINE OP SPLENIC FEVER 231 
 
 THE RETURN TO VIRULENCE . . . . . . .246 
 
 ETIOLOGY OP 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- 
 ioire dhin 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 
 
xii 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 multij)lication. 
 One hardly knows which to admire most — the in- 
 tuitive vision which discerns in advance the new 
 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 
 * infiinitely 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 crowed of connected 
 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 
 
INTKODUCTION. XUl 
 
 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 M. 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- 
 teur, speaks with such emphasis about * preconceived 
 ideas,' he does not mean ideas without antecedents. 
 Preconceived ideas, if oat 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 admkable 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- 
 Ime 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 m 
 rock-crystal, and which, without altermg chemical 
 constitution, destroyed crystalline identity. He first 
 found such facets in the tartrates, while he subse- 
 quently proved the neutrality of the paratartrate to 
 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 
 
xvi INTKODUCTION. 
 
 previously extracted from the two tartrates, acids which, 
 in regard to polarised Hght, 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. Kadot. 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- 
 symmetrically 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 
 
INTKODUCTION. XVll 
 
 of a dissymmetric molecule is not a very precise one, 
 even in the mind of M. Pastern*. 
 
 One word more with regard to the parentage of 
 preconceived ideas. M. Eadot 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 turniog 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. Eadot justly describes as * worthy of the 
 most serious consideration,' is sure to arrest the 
 attention of a large c'ass of people, who, dreading 
 * materialism,' are ready to welcome any generalisa- 
 tion v/hich 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 been 
 
XViii INTEODUCTION. 
 
 able to produce in the laboratory, by tbe 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. 
 Dissymmeii-ic forces, 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 mdiquer une separation plus profonde entre les 
 produits de la nature vivante, et ceus de la nature 
 mhierale, que cette dissymmetrie 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- 
 tmction 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 
 
INTEODUCTION. 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 coUeagues 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 M. 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 dissymra.etrical. 
 
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 jDlanes 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 apj)lies 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.' ^ 
 
 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.^ 
 
 ' Art. ' Vitality,' Fragments of Science, 6th edit., vol. ii. p. 50. 
 
 * 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 case of quartz, on being reflected 
 back through the body. Marbach has discovered that chlorate of 
 
INTEODUCTIOX. XXI 
 
 Theory, however, raay 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. Pastern- 
 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 
 crystal, while in quartz it occurs only in the direction of the axis. 
 Marbach also discovered facets upon his crystals, resembling those 
 of quartz. 
 
Xxii INTRODUCTION. 
 
 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 two 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, Penicillium glauciim. 
 
 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. XXIH 
 
 culties 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 au'. The fermentation of beer was sufficient 
 to suggest this idea. The yeast-plant, like many others, 
 can live either with or without free ah*. 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 torida 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 cerohies and ancsrohies, 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.' 
 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 cu-cumstances 
 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 destro}'". 
 This something consists of living organisms which 
 nourish themselves at the expense of the organic 
 substance, and cause its putrefaction. 
 
 The grasp of Pastern- 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 aceti, 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 
 
 ' It was late in the day when the Eoyal Society made him a 
 foreign member. 
 
INTRODUCTION. XXV 
 
 alcohol, tlie 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 defined the part played 
 by the Uttle 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. 
 2 
 
XXVI INTEODUCTION. 
 
 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 ]3articles 
 suspended m the air.' This means that living germs 
 cannot exist m 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 boUing 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. Pastern* 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. 
 
INTKODUCTION. XXvii 
 
 The manufacture and maladies of wine next 
 occupied Pasteur's attention. He had, m 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°rahr.) 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 
 
XXviii INTRODUCTION. 
 
 therefore to some extent at home m this new investi- 
 gation. The calamity was appaUing, 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 develox^ment 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. Eadot 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 : 
 
INTEODUCTIOK xxix 
 
 "Worms were infected by permitting them to feed for 
 a single meal on leaves over which corpusculous 
 mattsr 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 an. 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 ijelrine, 
 which was the principal scourge at the time. Another 
 formidable malady was also prevalent, called fiacherie, 
 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 
 
 ' 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.^ 
 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 om- Indian 
 or Colonial authorities if I reproduce it here : — 
 
 ' Permettez-moi de termmer 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 sole. 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 sole 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 
 
 ' The work on Diseases of Silkworms was dedicated to the 
 Empress of the French. 
 
rS-TRODUCTION, 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 the true torula or yeast-plant. Many 
 mysteries of om' 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. Pastern' 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 
 
xxxil INTKODUCTION. 
 
 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 {Mikhrand, Charhon, 
 Malignant Pustule), which seemed to me to mark an 
 epoch m the history of this formidable disease. With 
 admirable patience, skUl, 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 
 sjplenic fever. Davaine and Payer, in 1850, had ob- 
 served the little microscopic rods in the blood of 
 
INTEODUCTIOK 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 j)aj)er of the learned German 
 came the impulse towards a line of inqmry in which 
 M. Pasteur has achieved such splendid results. Things 
 presenting themselves thus to my mind, M. Piadot 
 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 occm' 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 ' 
 
XXXIV INTKODUCTION. 
 
 introduced by me in February 1877 was founded. The 
 difference between an organism and its spores, in point 
 of durability, had not escaped the i)enetration of 
 Pasteur. This difference Xoch showed to be of para- 
 mount importance in s^Dlenic 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 uifusions is 
 44° Cent. (111° Fahr.). The temperature of the blood 
 of bnds is from 41° to 42°. It is therefore close to 
 the prohibitory temperature. But then the blood 
 globules of a livmg 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- 
 peratm-e of a fowl to 37° 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 moculating a chilled fowl, per- 
 
INTRODUCTION. XXXV 
 
 mitting the fever to come to a head, and then remov- 
 ing the fowl, wrapped m cotton-wool, to a chamber 
 with a temperature of 35°. The strength of the 
 patient retiu'ned as the career of the parasite was 
 brought to an end, and in a few hours health was 
 restored. The sharpness of the reasonmg 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 
 m 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 demand 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 INTEODUCTION. 
 
 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 m 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 vkus. By successive cultiva- 
 tions of the parasite he showed, that after it had been 
 
INTEODUCTION. 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 
 hquid, 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. Eadot 
 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 un vaccinated. 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 niad dog should be referred to the animal's 
 
Xl INTKODUCTION. 
 
 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 inspkes 
 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 labom's ; 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. 
 
INTEODUCTION. 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 u^Don 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 m 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- 
 bUity of cholera. Such must always be the course of 
 things, as long as men are endowed with different 
 degrees of insight. 'V\Tiere the mind of genius dis- 
 cerns the distant truth, which it pursues, the mind 
 
xlii INTEODUCTION. 
 
 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. 
 
 EoTAL Institution : Beceniber 1884 
 
EECOLLECTIONS OF CHILDHOOD AND 
 YOUTH. 
 
 FIRST DISC0\':EEIES. 
 
 * Come, M. Pasteur ! you must shake off the demon 
 of idleness ! ' It was the night watcher of the College 
 of Besancon, who invariably at four o'clock in the 
 mornmg 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 coUege 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 
 
2 LOUIS PASTEUE. 
 
 have said had it been announced to him that fifty- 
 eight years later, on the fa9ade of the httle house in 
 the Eue des Tanneurs, would be placed, in the pre- 
 sence of his Hving son — laden with honours, laden with 
 glory, passing in the midst of a triumphal procession 
 along the jDaved town — a plate bearing these words in 
 letters of gold : 
 
 Here was boen Louis Pasteue, 
 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 j^oung girl, he 
 joined his lot with hers, and together they entered 
 courageously on the labours of then- 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 AND 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 malie 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 
 
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 Normale.' 
 
 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 
 hachelier 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 exammations of 
 the Ecole Normale. He must have been already 
 
EECOLLECTIONS OP CHILDHOOD A^^D 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 dm-ing 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 
 pupU pressed him no further, but having heard that at 
 Besancon 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 hohdays, 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 censm-e 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 sUent 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 PASTEUE. 
 
 Barhet, as the Franc-Comtois, with provincial fami- 
 liarity, used to call him. Pastern- 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 pupn by one-third. Such kindness was cus- 
 tomary with the pere Barhet, 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 Pastern* is received as fourth on the list. 
 Thus at last, in the month of October 1843, he finds 
 himself in that Ecole Normale in which he was 
 destined to take so great a place. Pastem-'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 Normale by M. Balard. The pupils of the Ecole 
 attended both courses of lectures. Different as were 
 the two i)rofessors, both of them exercised great influ- 
 ence on theh' pupils. M. Dumas, with his serene 
 gravity and his profomid 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 
 
EECOLLECTIONS 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 deske 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 
 
8 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 
 sph-it of research. There is in it an element of 
 superiority over the Ecole Polytechnique. 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. 
 
FIKST DISCOVERIES. 
 
 I. 
 
 Unlike the old professor of physics and chemistry 
 at Besangon, 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 Eetz, 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 PASTEUR. 
 
 siDecific 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, then- 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 natm'e and number 
 of the atoms, thefr 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 
 
FIKST DISCOVEEIES. 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 bm'eau of the Minister of Educa- 
 tion, and spoke of his assistant in terms which caused 
 the nomination to be cancelled. Pasteur remamed 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 labyi'inth 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 MitscherHch 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 ^vould have done well, out of con- 
 sideration for those who love to sj)eak 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 1 
 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 withm the range of his hearers, he 
 said — 
 
 ' If you picture to yourself all the bodies in natm'e 
 — 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 chan, a playing 
 
riEST DISCOVEEIES. 13 
 
 die, or tlie 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 PASTEUE. 
 
 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. Eock 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 spkal, 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 
 
riEST DISCOVERIES. 15 
 
 before a mirror ; the image faitMully reproduces the 
 chair. The mu'ror also reproduces the human body- 
 considered as a whole. But place before the muTor 
 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 interestmg 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 iDlane 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 — w^hile 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. 
 
FIEST DISCO VEKIES. 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 
 
18 LOUIS PASTEUE. 
 
 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 DISCOVEEIES. 19 
 
 Balard. 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 m 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 
 thkty or forty grammes of crystals, he begged me to 
 go over to the CoUege 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 
 han^l, 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 
 
20 LOUIS PASTEUE. 
 
 the inquiry. M. Biot then prepared the solutions in 
 well-measured proportions, and at the moment of 
 observmg 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 j)rofound 
 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 
 
FIEST DISCOVEEIES. 21 
 
 left-lianded tartaric acid, with its truly surprising 
 properties, had been discovered ; molecular physics 
 and chemistry had been em'iched with new facts and 
 theories of great value. 
 
 The first care of Pastern', after ha\'mg 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 nicture the exact figure of these atomic 
 groupmgs, 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 ^regular pyra- 
 mid, the arrangement of the atoms of the left-handed 
 tartaric acid ought, of necessity, to present the form 
 of a pyramid irregular m 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 
 
FIEST DISCOVERIES. 23 
 
 one ease 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 memoires of the Academy. 
 This was an exceptional honour. Arrived for the most 
 
24 LOUIS PASTEUE. 
 
 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 DISCOVEEIES. 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 crystalhsed, 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 
 changmg 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 PASTEUE. 
 
 occasion new facets "were thus produced, and these 
 new facets showed the kind of dissymmetry which the 
 oj)tical 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 
 
FIEST DISCOVEKIES. 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, m'ic acid, creatine, &c. None of these pro- 
 ducts exert an action on polarised Ught or show any 
 dissymmetry in the form of then 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 suf&cient to establish 
 their internal dissymmetry, even when, through the 
 absence of crystallising power, they fail to manifest 
 this dissymmetry outwardly. 
 
28 LOUIS PASTEUE. 
 
 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 mdicate a more profound 
 distinction between the respective products of living 
 and of mmeral 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 tm*pentine, 
 &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. 
 
FIEST DISCOVEEIES. 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 au' 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 mh'ror an image not superposable on the reality. 
 Even the motion of solar hght is dissymmetrical. A 
 luminous ray never strikes in a straight line, and 
 
30 LOUIS PASTEUE. 
 
 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 
 labom'S 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 then- aid, among the forms of crystals, a mani- 
 festation of dissymmetry. At Lille, w^here 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 
 dhection and then in the other. ' All this was gross,' 
 he said to me one day ; ' but, fm-ther 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 mhror, the motion of the solar rays 
 which should strike them from the birth of their 
 earhest shoots, and in this direction there was more 
 
FIRST DISCOVEEIES. 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 untU 
 we have succeeded in introducing among these re- 
 actions influences of the dissymmetric order. Accord- 
 ing to Pasteur, success in this du'ection 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^) 
 
 ' [M. Pasteur appears to use the word devenir as a substantive 
 in a sense equivalent to the German Werdende.^ 
 
32 LOUIS PASTEUK. 
 
 proper to the species, a tendency which is jDotential 
 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 
 
 wlio 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 mahc acids. Eeturn- 
 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.' 
 
riEST DISCOVEKIEa 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 
 
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 j)roperties 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 m 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 ordmary 
 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 j)rocess of 
 fermentation the liquid mass, previously limpid, be- 
 came gradually turbid, in consequence of the appear- 
 
FIKST DISCOVEEIES. 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 com-se 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 the seed of penicillium glaucwm, 
 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 futm'e reserved for researches which have this 
 influence for then- 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 PASTEUE. 
 
 FERMENTATION. 
 
 Aeer^ed at this unexpected turn in the road which 
 he had hitherto pursued, Pasteur paused for an in- 
 stant. Should he commit himself to the com-se "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 necessiiy is not absolutely demon- 
 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 
 
FEEMENTATION. 41 
 
 he conld 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 
 he some great general law. 
 
 I. 
 
 All that has lived must die, and aU 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 aU 
 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 au\' 
 
 The oxygen of the au* 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. 
 
FEEilENTATION. 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 the primum 
 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 PASTEUR. 
 
 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. Eepeating 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- 
 tion. 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 buddmg of the yeast globules there must 
 be some clue to the phenomenon of fermentation. I, 
 however, repeat that as nothmg 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 
 
FEEMENTATION. 45 
 
 being in contact with air. It is the dead portion of the 
 yeast — that which has Hved and is in the course of 
 alteration — which acts upon the sugar. 
 
 The new memoirs puHished on the subject agreed 
 in rejecting the hypothesis of any influence whatever 
 of organisation or of hfe in the process of fermentation. 
 Books, memoh'S, 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 
 theh centres, extremely small, being hardly the thou- 
 sandth part of a millimeter in diameter.^ 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 mto two, and 
 so on. Why had not this been observed prior to 
 
 ' [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 preserving 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 the 
 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 Academy 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 disappearmg, 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 
 Pastern'. 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 PASTEUR. 
 
 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 
 
FEEMENTATION. 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 iDure 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 organication 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, origmating 
 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 PASTEUK. 
 
 augmented in weight, feeding upon the sugar, and its 
 vitahty 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 
 
FEEMENTATION. 51 
 
 motion, which up to that time had reigned in ccience, 
 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 thek 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 infusoriee may be sown like the yeast 
 of beer or the lactic ferment. If the medium in 
 
52 LOUIS PASTEUR. 
 
 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 
 
FEHMENTATIOK 53 
 
 fall without movement to tlie 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 anaerohies ; that is to say, beings which 
 can live without air. He reserves the designation 
 aerohies 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 Hquid 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 
 certamly 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 fermentation manifests an activity even 
 
56 LOUIS PASTEUE. 
 
 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 ah' for then- 
 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 Hfe of a micro- 
 scopic organism, continued without interru]3tion. 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 PASTEUR. 
 
 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- 
 comj)osition 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 animalculae, 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 Liebig mentioned these hypothetical 
 opinions. 
 
 ' Those who pretend to explain the putrefaction 
 
FEEMENTATION. 59 
 
 of animal substances by the x^i'esenee of animalcule,' 
 he 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 tm'n what is the 
 cause which determines the putrefaction of the fungus 
 or of the micro:copic animalcula when life is with- 
 drawn fi-om these two organisms ? ' 
 
 Thh'ty-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. BouiUaud, asked, 
 with the insistent voice of a querulous octogenarian : 
 * Let M. Pasteur then tell us here, in presence of the 
 Academic de Medecine, what are the ferments of the 
 ferments.' 
 
 Before replying to this argument, which Liebig 
 and M. BouiUaud 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. 
 
 atmosj)heric 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 pro]3ortion 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 
 
FEBMENTATIOX. 61 
 
 the work of microscopic anaerobies, liying without free 
 oxygen, the slow combustion is found very largely, if 
 not exclusively, to depend upon a class of infinitely 
 small aerobics. It is these last which have the pro- 
 perty of consuming the oxygen of the air. It is these 
 lower organisms w^hich-are the powerful agents in 
 the retm-n to the atmosphere of aU which has lived. 
 Mildew, mould, bacteria, which we have already 
 noticed, monads, two thousand of which would go to 
 make up a millimeter, aU these microscopic organisms 
 are charged with the great work of re-establishing the 
 equihbrium of life by giving back to it aU 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 aU dust. This process we shaU 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 httle seeds 
 
62 LOUIS PASTEUR. 
 
 of mould suspended in the air, or associated with the 
 substances contamed in the vessels, neither did he 
 avoid other infinitely small germs of the class 
 aerobies. 
 
 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 hfe 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 dhectly and chemically 
 when the infinitely smaU organisms are absent. 
 
 But can these microscopic organisms, after having 
 decomposed or bm-nt up aU 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 retm-n to the atmosphere ? After having 
 
FERMENTATION. 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 ah'. 
 Leave this mass to itself in summer temperature, and 
 you will see appear in the interior of the mass ana- 
 erobic vibrios and the putrefactions associated with 
 their life when protected from contact with the ah'. At 
 the same time, on the surface of the enthe 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 aerobics. The portion of 
 the aerobics which has lived becomes the prey either 
 of new aerobies of different species, or of individuals 
 of then* 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 PASTEUE. 
 
 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 j)henomena 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 hfe 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 au\ 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 ah*, 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, these combustions 
 will continue. "Wliile 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 PASTEUE. 
 
 ACETIC FERMENTATION. 
 
 THE MANUFACTUEE OF VIXEGAE. 
 
 Soon afterwards Pasteur came upon a most curious 
 illustration of the ' fixation ' of atmospheric oxygen by 
 a microscopic organism — the transformation of "wine 
 into yinegar. As its name indicates, yinegar 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 
 ipresence 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 FEEMENTATION. 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 remaias 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. '\^Tien distilled it yields water 
 and a sphit. 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 smeUing bottles — in those bottles of English 
 salts the vapom* 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. 
 
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 vokime, and the oxygen of 
 one-fifth. Well, in the transformation of wine into 
 vinegar the nitrogen remains inactive. It is the 
 oxygen pJone 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 an*, 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 fiU the partial vacuum 
 created 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 om- knowledge to what has gone 
 before, it would seem that alcohol diluted with water 
 and exposed to the air ought to fm*nish acetic acid. 
 It is not so, however. Pure water alcohoKsed 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 an* 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 altera^tion, 
 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, dUuted 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 PASTEUE. 
 
 it is a plant, and of all x^lants one of the simplest and 
 most minute, whicli has been known from time imme- 
 morial under the name of flower of vinegar. This 
 Httle fungus is inyariably present on the sm-face 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 an it becomes covered with a cryptogamic vege- 
 tation, or is invaded by a crowd of animalculas ? 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 Httle microscopic fungus, by this 
 flower of vinegar, this mycoderma 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 temperatm-e 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 bsfore 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 tile 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, 
 accomphshes all. 
 
 Is there not a great charm in seemg 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 ak, 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 FEEMENTATION. 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. WHien 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 the JixatiGn of this gas upon the alcohol, which 
 
74 LOUIS PASTEUK. 
 
 is thereby transformed into acetic acid. The Httle 
 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 w^here 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 wiue — a manufacture which justly makes 
 the reputation of the town of Orleans ? Take some 
 wine, and after having mixed with it one-fom-th 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 hquid 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 fihn, 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 FEEMENTATION. 75 
 
 forty-eight hours at most, the mycoderm covers the 
 whole Hquid, 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 mycoderma 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 PASTEUR. 
 
 instead of regularly reflecting it, as does tlie 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 then- feet, or with their probosces, these flies 
 transport the seed. 
 
 At Orleans the process for the manufactm-e of 
 vinegar is very simple. Barrels ranged over each 
 other have on each of their vertically-placed bottoms 
 a ch-cular 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 FEKMENTATION. 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 ' 
 begm. 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 
 mvolves 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 locaHty to 
 another. The 'mother,' m fact, must rest immovable. 
 
 Pasteur advised the suppression of the ' mothers.' 
 He recommended an ap^Daratus, 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 FERMENTATION. 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 PASTEUE. 
 
 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 FEEMENTATION. 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 defiled 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 filHng 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 
 sk)wer, 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 Httle 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 
 tor 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 FEEMENTATION. 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 termmated 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. 
 
84 LOUIS PASTEUR 
 
 ' 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 FEKMENTATION. 85 
 
 require, and lie 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, nothmg 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 
 milliemes of acetic acid to trickle slowly into barrels 
 or vats filled with shavhigs of beech, either massed 
 
86 LOUIS PASTEUR. 
 
 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 
 stUl, 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 montlis or even for 
 several years are examined, they are found to be extra- 
 
ACETIC FERMENTATION. 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 sm'faces 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 then- 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,' rejjlied 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. 
 
THE QUESTION OF SPONTANEOUS 
 GENERATION. 
 
 * All dry bodies,' said Aristotle, ' whicla become damp, 
 and all damp bodies which are di'ied, engender animal 
 life.' Bees, according to Yirgil, 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, Yan 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 dnty 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 
 suf&ces to pair them.' 
 
 ' Scoop out a hole,' said he agam, ' 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, Eedi, 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 larvaB of flies' eggs. To prevent 
 the production of maggots, Eedi showed that it was 
 only necessary to surround the meat with fine gauze 
 before exposing it to the ah*. 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 exj)lain 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 Enghsh Catholic 
 priest Needham adopted the theory of spontaneous 
 generation, the Itahan 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 
 emjphatic 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 PASTEUE. 
 
 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 OE 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 chan*, 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 CoUege de 
 France. 
 
 At the time here referred to, the Minister of Public 
 Instruction said to Pastern-, ' 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 projDOsed 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 PASTEUE. 
 
 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 httle 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 mercmy, 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 PASTEUE. 
 
 cause of his error ; this is what has vitiated his whole 
 arrangement.' 
 
 Pasteur then instituted experiments exactly similar 
 to those of Pouchet, but taking care to remove every 
 cause of error which had escaped the latter. He em- 
 ployed a glass bulb 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 OE SPONTANEOUS GENEEATION. 99 
 
 mercury. In these circumstances ebullition goes on 
 under a pressure greater than that of the atmo- 
 sphere, consequently at a temperatm'e higher than 
 100 degrees Centigrade. 
 
 It remained, however, to be proved that the floating 
 dust of the au- embraces the germs of the lower 
 organisms. Through a tube stopped with cotton 
 wool, Pasteur, by means of an aspirator, drew ordi- 
 nary ah'. In passing through the wool it was filtered, 
 depositing therein aU 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 
 aU the intercepted dust. The operation is simple and 
 easily executed. Placing the glass slide with a little of 
 the soiled liquid under a mieroscoj)e, we can dis- 
 tinguish particles of soot, fragments of silk, scraps of 
 wool, or of cotton. But, in the midst of this inani- 
 mate dust, living particles make their appearance — 
 that is to say, organisms belonging to the animal or 
 vegetable kingdom, eggs of infusoria, and spores of 
 cryptogams. Germs, animalculae, flakes of mildew, 
 float in the atmosphere, ready to faU into any appro- 
 priate medium, and to develop themselves at a pro- 
 digious rate: 
 
 But are these apparently organised particles 
 
100 LOUIS PASTEUR 
 
 "whicli are found thus associated -with amorphous dust 
 indeed the germs of microscopic Hving bemgs ? 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 ah* which has 
 passed through a red-hot platinum tube canwot pro- 
 voke fermentation, or putrefaction, or the formation 
 of organisms, because the germs of these last, •which 
 were suspended in the ah', 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 ? Xow, by ihe passing of the 
 ah' 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 
 X^roof that the cotton wool through which his air had 
 filtered was really charged with germs. 
 
THE QUESTION OF SPONTANEOUS GENEEATION. 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 hquids 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 contamed in the cotton wool? Only 
 amorphous particles of sUk, cotton, starch; and, 
 along with these, minute bodies which, by then* 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 stUl 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 PASTEUK. 
 
 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 m 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 aU. 
 
 If, after remaining for weeks, months, or even 
 years, in a heated chamber, the smuous 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, 
 ' take up a little of this outside dust on a bit of glass, 
 porcelain, or platmum, 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 Uttle drop 
 7 
 
104 LOUIS PASTEUE. 
 
 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 then- 
 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 m 
 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, whUe 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 ah" — 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, be 
 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 dm*ing 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 fi'om 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 degTees 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 du'ectly 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 afiirming this fixed con- 
 viction. With the authority of a judge delivering 
 sentence in com-t, 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 
 animalculse ? 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 atmosj)here a 
 certain quantity of an 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. Pouchet, 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 Hving 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 GENERATION. 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 exa<it 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 doctririe. Pec pie 
 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 solyed the problem of Bi^ontaneous 
 generation, a problem wliicli was but a parenthesis 
 forced upon his attention, Pastern* returned to fer- 
 mentation. Guided by his studies on vinegar and 
 other observations of detail, he undertook an inqmry 
 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 
 beheved 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.' TMien the fermentation of the gi'ape is 
 finished, equilibrium is not quite estabhshed 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 nothmg 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 com-se of time, and similar reactions 
 perhaps take place between the other constituents of 
 the Kquid. 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- 
 
114 LOUIS PASTEUE, 
 
 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 multii)lication 
 of microscopic vegetations. Such growths alter the 
 wine, either by subtracting fi'om it what they need for 
 then- nourishment, or, and princiimlly, by forming new 
 products which are the effect of the multipHcation of 
 these parasites in the mass of the wine. 
 
 Everyone knows what is meant by acid wine, 
 sharp uine, sour wine. The former experiments of 
 Pastern- had clearly shown that no Vtine can become 
 acid, sharp — can, in a word, become vinegar — without 
 the presence of a Httle microscopic ftmgus known by 
 the name of mycoderma aceti. This little plant is the 
 necessary agent in the condensation of the oxygen of 
 the au', 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 reqidrements 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 
 
116 LOUIS PASTEUE. 
 
 itself felt in the A-intage tubs. The wine is said to 
 turn, to rise, to sjmrt. The wine becomes shghtly 
 turbid and at the same time flat and piquant. 
 When it is poui'ed into a glass, very small bubbles 
 of gas form like a crovrn upon the surface. On 
 placing the glass between the eye and the light 
 and shghtly shaking it, one can distinguish silky 
 waves shifting about and moving in different direc- 
 tions in the liquid. AMien the turned wine is in a 
 cask, it is not unusual to see the bottom of the cask 
 bulge a httle, and sometimes a leakage takes i^lace 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 beheved 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 fi'om 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 miKes 
 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 other, forming a glutinous mass, 
 which under the microscope is seen to be comjDosed 
 entnely 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 
 httle gas-bubbles, observed when the tm^ned 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 sm'face of the grapes at the 
 moment of gathering them, or on spoUt grapes such 
 as are found in every vintage. It is very rare 
 not to find this parasite of tm^ned wine in the de- 
 
118 LOUIS PASTEUR 
 
 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. Eed 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 
 only does 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 limi3idity ; 
 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 WINK. 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 tho 
 wine. 
 
 In short, according to Pastem-'s observations, the 
 deterioration of wines should not in any case be attri- 
 buted to a natural working of the constituents of the 
 wine, proceeding from a sort of interior spontaneous 
 movement, which would only be affected by varia- 
 tions of temperature or atmos]jheric 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 spoUt 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, 
 BO numerous, and possessing in a more or less marked 
 degree the anaerobic character, should find at certain 
 
120 LOUIS PASTEUR. 
 
 moments, in the state of the wine, the right conditions 
 for their existence and multipHcation ? 
 
 The cause of these alterations having been found, a 
 mode of preventing the development of all these para- 
 sites had stUl 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 secm*e 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 dh-ected 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 stu'red up. "\\Tien 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 Hght, 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 PASTEUR 
 
 priority "will find described in the works of Latin 
 agricultui'ists 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 then' retm'n 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. de 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 Pastem-'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 wme, 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 reaHse 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 wu-e 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* efibrts 
 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 PASTEUE, 
 
 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 neutrahsing them. By the 
 application of heat, and without producmg any change 
 in the colour or flavour of the wines, he had been able to 
 insm-e then- 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. 
 
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 sUkworm- 
 rearing establishments exist everywhere. When people 
 accost each other, instead of saying ' How are you ? ' 
 they say ' How are the sUkworms ? ' 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! WiU 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 days 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 then- golden 
 prisons and become clnysalides. "WTiat days of rejoicing 
 are those in which the cocoons are gathered ; when, 
 to use the words of OUvier 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 httle 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 SILKWOKM-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 thhty hours. Presently, its head 
 moves, as if it did not belong to the rest of the body, 
 and mider 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 (fausses pattes), 
 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 chrysahs. 
 
130 LOUIS PASTEUE. 
 
 "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 fom' to six hundred. These are aU 
 the phases through which silkworms pass in the space 
 of two months. 
 
 In the epidemic which ravaged the silkworm nm-- 
 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 fii'st days of their existence. 
 Often the hatching was excellent, and the worms ar- 
 rived at then- 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 aU the worms going through 
 
THE SILKWOEM-DISEASE. 131 
 
 the phases of this first moulting together, as is usually 
 the case in a batch of silkworms, they began to present a 
 marked inequahty, 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 favom'ably to the thii-d, and even to the fourth 
 moulting, the uniform size and the health of the 
 worms leaving nothing to be desired ; but after the 
 fom'th moulting the alarm of the husbandman began. 
 The worms did not tm-n white, they retained a rusty 
 tint, their appetite diminished, they even turned 
 away fi-om 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 Ktter, 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 
 
132 LOUIS PASTEUR. 
 
 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 be 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 cam« 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 sus^^ected 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 sulphm', 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 Agricultm'e 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 sUk husbandry, his sympathy for one of the depart- 
 ments most severely smitten, the Gard, his own native 
 place, aU contributed to cause him to be nominated 
 Eeporter 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 PASTEUK. 
 
 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. Dumas. * If yon 
 know nothing about the subject, you wiU have no 
 
THE SILKWOEM-DISEASE. 135 
 
 other ideas than those which come to you from your 
 own observations.' 
 
 Pastern: 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, Pastern- 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 naturaUsts, especially Filippi and Cornaha, 
 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 sUkworms' eggs, and Dr. Yittadini had 
 proposed to examine the eggs with a microscope in 
 order to secm^e having sound ones. M. de Quatre- 
 fages only mentioned this matter of the corpuscles as 
 
136 LOUIS PASTEUE. 
 
 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 microscoj)e. This instrument 
 had already rendered such services to Pastern- 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 Normale. 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 cultm-es 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- 
 cles 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 
 occur. But what would happen when the worms of 
 the bad group spun their cocoons? Pasteur found 
 that in the chrysalides, especially in the old ones, the 
 corpuscles were numerous. As regards the moths 
 proceeding from these cocoons, not one was free from 
 them, and they existed in profusion. 
 
138 LOUIS PASTEUE. 
 
 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 SlLKWOEil-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 aU doubt that the corpuscles were 
 a normal element of certain worms, and especially of 
 aU the moths when old; that other authors had 
 affirmed it to be sufficient to starve certain worms to 
 make these famous corpuscles appear in aU 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 
 ItaHan entomologist Cornalia ; * your selected eggs wiU 
 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 nestlmg among 
 the trees called Pont-Guisquet became at the same 
 time his habitation and his sUkworm 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 
 takmg part in all the experiments. The assistants 
 of the Ecole Normale, Duclaux, Maillot, Gernez, 
 
THE SILKWOEM-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 Pastern' 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 PASTEUK. 
 
 influence. Pasteur soon succeeded, by accurate ex- 
 periments, in proving absolutely that the evil was 
 contagious. 
 
 One of the first experiments V7as 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 ]3assed 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 SILKWOEM-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 sUkworm 
 nurseries, especially the symptom of spots on the 
 skin, which had led to the disease being called pehrine. 
 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 pehrine on 
 the skin, far from being the disease itself, were but 
 
144 LOUIS PASTEUK. 
 
 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 pehrine,' 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 th-ed 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 SILKWOEM-DISEASE. 145 
 
 of corpuscles. Such motlis 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 then- usual health. Could there be a 
 better proof that the corpuscles alone were the real 
 cause of the pehrine 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- 
 
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 havmg observed in the 
 worms either spots of pehrine 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 SILKWOEM-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 
 a healthy worm passing over the body of the corpus- 
 culous worm. The hooks of the first worm, by pene- 
 tratmg 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 
 
148 LOUIS PASTEUR. 
 
 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 pehrine 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 
 pehrine 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 easily understood than the 
 
THE SILKWOEM-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 
 normal purity, but associated with a parasite which 
 will find in the materials surrounding it, so adapted 
 to hfe and transformation, the elements of its own 
 nourishment and multipUcation. 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 LOmS PASTEUE. 
 
 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 nurtm'e 
 of the worms. Whatever might happen, or whatever 
 might be the cause of ruin in a sUkworm 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 gu-ls, even by children. It was 
 
THE SILKWOKM-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 
 9 
 
152 LOUIS PASTEUE. 
 
 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-Jiats, ox flacherie. 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 oi pebrine y^fithjiacherie. 
 
 These suspicions were confirmed by his cultiva- 
 tions of April and May. Numerous cases of Jiacherie 
 presented themselves. Uncertainty was no longer 
 possible as to the mutual independence of the two 
 maladies — pebrine and jiacherie. 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 SILKWOEM-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. Pehrine was e"sddently 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 temperatm'e 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 aU 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 sm-face 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 fiUs it from one end to the other 
 
154 LOUIS PASTEUE. 
 
 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 ah*-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 then* 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 ! Pastern^ proved that when- 
 ever a worm was attacked with flacherie, 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 SILKWORM-DISEASE. 155 
 
 which digests badly is doomed to perish of flaclierie, 
 or to furnish a chrysahs and a moth the life of which, 
 through the injm-y produced by organised ferments, 
 is not normally perfected.' 
 
 Thus, as in the case of pebrine, the morbid sym- 
 ptoms of flacherie are very variable. All depends on 
 the intensity of the evU — 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 mortahty 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, faUing, remain 
 
156 LOUIS PASTEUE. 
 
 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 then- cultm^e. 
 
 Too large an assemblage of worms in one nursery ; 
 too high a temperatm^e 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 tendmg his precious ' kine,' 
 to use an expression of the sixteenth centm-y. 
 
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 wear 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 wHl suitably 
 diminish the fire.' 
 
 One point which had been ignored before the ex- 
 periments of Pasteur was the contagious character of 
 flacherie. This contagion may surpass that of 'pehrine 
 itself as regards dm-ation. In 'pehrine 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 hfe. Deposited 
 on the leaves which are to serve as nourishment. 
 
158 LOUIS PASTEUE. 
 
 these germs of vibrios are carried into the intestinal 
 canal of the worm, develop and multiply themselves, 
 and completely distm*b the digestive fmictions, 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 pehrine and 
 Jlacherie, Pasteur reproduced fiacherie, and not pehrine. 
 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 i^ehrine, 
 the excreta of the worms attacked by jlacherie, 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 fiacherie, 
 hygienic precautions are sufficient. As regards here- 
 ditary j^ac^me, 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 SILKWOEM-DISEASE. 159 
 
 salides, and the moths destmed to produce the eggs. 
 Every attention should be dhected to the complete 
 exclusion of ferments from the intestinal canal of the 
 worms, and from the stomach-pouch of the chrysahdes — 
 a httle 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 m 
 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 then* Hfe, so as to make sure of thek vigour at the 
 moment when they spin thek silk. If you use eggs 
 produced by moths the worms of which have mounted 
 the heather with agility, have shown no signs of 
 Jlacherie between the fourth moulting and mounting 
 time, and do not contain the least corpuscle of pebrine, 
 then you wiU 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 PASTEUE. 
 
 pelled. Pasteur had arrived at sucli 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 flacherie. 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 procm'ing 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 certamty. 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 flacherie 
 was easy, but there remained the struggle against 
 pehrine. 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 jfinished, and the 
 
THE SILKWOEM-DISEASE. 161 
 
 appearance of the moths alone is waited for. They 
 arrive, and they pah. Then begms 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 m 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 
 leism*e, 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 
 Prome, 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 
 
TKE SILKWOEM-DISEASE. 163 
 
 the body, ended by triumphing over the affliction. 
 Paralysed on the left side, Pasteur never recovered the 
 use of his hmbs. To this day, sixteen years after the 
 attack, he limps hke a wounded man. But what 
 stages had this wounded man yet to travel over, what 
 triumphs were yet in store for him ! 
 
164 LOUIS PASTEUR. 
 
 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 
 
DECLSIYE EXPEEIMENTS. 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 
 earhest 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- 
 chah', Pasteur du-ected 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 then' phases, from the egg 
 up to the cocoon, the cultivations there undertaken, 
 and he had the happiness of proving once more the 
 cerfcainty 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 EXPEKIMENTS. 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 PASTEUE. 
 
 STUDIES ON BEER. 
 
 The \\'ar was over. Little by little the life of the 
 country was resumed, and with returning hope the 
 deshe 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 pm-pose 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 BEEE. 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. WhUe 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 PASTEUE. 
 
 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 
 Hquid would be obtamed. 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 du-ect 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 PASTEUR. 
 
 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 Mere 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 BEEE. 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, turn6d, 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 PASTEUE. 
 
 preservative ? But beer is a drink necessarily charged 
 with carbonic acid, and the appHcation 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 EEEE. 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 dlionneur 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.' 
 10 
 
176 LOUIS PASIEUE. 
 
 VIRULENT DISEASES. 
 
 SPLENIC FEVER (cHARBON) — SEPTICEMIA. 
 
 * He that thoroughly understands the nature of fer- 
 ments and fermentations,' said the j^hysicist 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 livmg 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 forvsrard, 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. 
 
178 LOUIS PASTEUE. 
 
 The opposite doctrines of Liebig and Pasteur 
 are here brought into clear juxtaposition ; and thus 
 was theu' 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 memou' 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 m-ine 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 sm-geon hastened to follow this advice, and 
 with the most happy results. "V\'Tiile attributing to 
 Pastern- the honour of this discovery, M. Guyon, in 
 one of his lectures, said : — 
 
 ' Boracic acid has this immense advantage, that it 
 can be applied m large doses— 3 to 4 per cent. — with- 
 out causing the slightest pain. It has therefore 
 become, in our practice, the agent continually and 
 
VIEULENT 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- 
 quu-ed, and I never wash the bladders of lithotritised 
 patients with any other substance. I have also had 
 good results fi'om 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 u-rigations 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 Pastem-'s researches important thera- 
 peutic appUcations. In 1865 Dr. Lister began in 
 Edinburgh the brilliant series of his triumphs in 
 sm-gery 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 sm'geon, he ^^Tote 
 to Pastern- 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 
 memou' 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 
 
180 LOUIS PASTEUE. 
 
 the antiseptic system wliicli 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 of the germ theory 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 dhection. '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, obhged 
 
VIBrLENT DISEASES. ISl 
 
 liim to go forward. In February 1S76 Tyndall wrote 
 to him thus : — 
 
 * In taking np yonr researches relating to infosorial 
 organisms, I have had occasion to refresh my memory 
 of yom: labours ; they have revived in me all the ad- 
 miration which I felt on first reading them. It is my 
 intention to foUow 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 
 dehvered 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 aU the causes of the terrible malady 
 called splenic fever {charbon , Germ. Mihbrand), 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 aU 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 attaclced 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 sang-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-Loh' 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, tanngrs, 
 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 Em'e-et-Loir, Dr. Rayer, givmg 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 s^Dlenic 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. Eayer and Davaine also paid no atten- 
 tion to them. This indifference lasted for thhteen 
 years ; it would have lasted longer still, if the parasitic 
 origin of communicable diseases had not been brought 
 before the mmd 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 Eayer 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 dkect from the bladder, could be 
 exposed to the contact of pure ah* 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 
 
"VIEULENT DISEASES. 185 
 
 a great analogy with these vibrios, I was led to 
 examine whether filiform corpuscles, analogous to or of 
 the same kmd 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 multiphcation in the blood, it 
 
186 LOUIS PASTEUE. 
 
 without doubt produces in the constitution of this Hquid, 
 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 moculated rab- 
 bits and dogs with various putrefying hquids 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 hquids, they failed to generate any virulence 
 in the blood. Davaine had no difficulty in showing 
 that IVIM. 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 entu'elv new and unexpected experi- 
 ments. They inoculated some rabbits, as Davaine 
 desii-ed, with the blood of a cow which had died of 
 splenic fever. The rabbits died rapidly, but without 
 showing before or after then- 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 then- 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 siDlenic 
 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 fm-nished to us by the dkector of the 
 knacker's establishment of Sours, near Chartres, and 
 this dh-ector is mideniably competent as to the know- 
 ledge of splenic fever.' 
 
 Full of sincerity and conviction, MM. Jaillard 
 and Leplat recommenced then- 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 PASTEUE. 
 
 obtained with the blood of the cow. Notwithstand- 
 ing the repKes of Davaine, which, however, added 
 nothing to the facts ah-eady 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. 
 
VIEULENT 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 PASTEUK. 
 
 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 Eollin. 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. 
 
VIEULEKT 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 wnputrescible 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 in 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 durmg 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 vu'us. 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 their 
 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. 193 
 
 hypotheses, they allowed themselves to be deceived by 
 false assimilations to facts of a pm'ely 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 multipHed 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 w^as 
 necessary to throw light upon the facts, mamly 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 rajpidly, and the blood of these 
 rabbits was shown to be also virulent. It was suffi- 
 cient to moculate 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 
 
194 LOUIS PASTEUE. 
 
 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 hght 
 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- 
 
VIEULENT DISEASES. 195 
 
 ing to the respective laws of their eyolution 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 hquid 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 tha 
 time of death. Nothing is more striking than the rapid 
 inflation and almost immediate putrefaction of animals 
 which have succumbed to splenic fever. Of aU 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 fi'om then- 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 fii'st following hom^s contained exclusively 
 the parasite of splenic fever, harbom-s at one and 
 the same time both the 'bacillus of splenic fever 
 
196 LOUIS PASTEUR 
 
 and the septic Tibrio. Then occur the very curious 
 effects arising from the anaerobic nature of these 
 vibrios, and their opposition to the bacilhis of splenic 
 fever, which is exclusively aerobic. Diffused m blood 
 deprived of oxygen gas, the splenic bacillus scon 
 perishes. In its place are to be found amorphous 
 granulations deprived of all vkulence. 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 pecuHarities of the splenic bacilli and the septic 
 vibrio, it results that if, in order to inoculate an 
 animal capable of contracting the fever, a di'op of blood 
 be taken from one that has just died of it, and if the 
 operation is performed during the fii'st 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 wiU 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. Jaillard 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 hom's. 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 
 septicaemia may be said to correspond to every sort of 
 vibrio of putrefaction. 
 
 Such were the circumstances which, without their 
 
198 LOUIS PASTEUE. 
 
 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, ^ven 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 
 Pastem-'s discovery as to the mode of reproducing the 
 
"V^EULENT 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 j)oints, 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 
 11 
 
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 j^athogenic 
 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 
 
VIEULENT 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 Tm-in, regarding 
 the facts above mentioned. One experiment, in the 
 success of which Pasteur was extremely interested-, 
 had been made at this school. Instead of emplojdng 
 pure splenic fever blood, fi-ee from all contagium, the 
 Italian professors, whether from ignorance of the pre- 
 ceding facts or from madvertence, employed the blood 
 of a diseased sheep, which, from theii- own showing, 
 had been dead more than twenty-fom- 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 PASTEUE. 
 
 a microscope, had had this sheei)'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 j)ublic 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-fom' 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- 
 
VIEULENT DISEASES. 203 
 
 ever he be, ' Je vous 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 ' Pastern-, ' take 
 care ! Pastern- is never mistaken.' 
 
 One day, in 1879, a professor attached to a facnlty 
 of medicine in one of the provmces 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 x)erplexed the doctor very much. He 
 wrote to Pasteur that he did not dispute the affirma- 
 tion, but that he proi)osed 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 yom- eyes. You 
 
204 LOUIS PASTEUE. 
 
 ■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 hy 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 sj)lenic 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 saptic vibrios. If air de- 
 stroys them, if their culture is impossible in contact 
 with air, how can septicaemia exist, since an* 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 au% 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 cm-ious spectacle 
 wUl be witnessed : In the upper layers the oxygen of 
 the ah' 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 briUiant 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. 
 
VIEULENT DISEASE^. 207 
 
 II. 
 
 In these two viruleut maladies, then, splenic fever 
 and septicaemia, the researches of Pasteur had clearly 
 established the parasitic theory. A grand and novel 
 opening was made for futm*e 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 stiU 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 imable to 
 
208 LOUIS PASTEUE. 
 
 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, -^"ho 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 Hquid 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 
 ever}^where. 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 bhds 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 temperatm-e 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 livmg 
 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 PASTEUE, 
 
 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 hve in this 
 blood ? ' 
 
 The experiment was made. A hen was taken, and, 
 after inoculatmg it with splenic fever blood, it was 
 placed with its feet in water at 25 degrees. The 
 temperatm-e of the blood of the hen went down to 
 37 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 j^laced in an 
 oven at a temperature of 35 degrees. Little by little 
 its strength retm-ned; 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 
 shghtest 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 Hfe 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. 
 
212 LOUIS PASTEUE. 
 
 FOWL CHOLERA. 
 
 If fowls are naturally impervious to the infection of 
 s]3lenic 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 b}^ 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 Tmin, M. Peroncito, depicted it in 1878 ; 
 
FOWL CHOLEEA. 213 
 
 a professor of the veterinary school of Toulouse, M. 
 Toussamt, 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 
 cultivatmg 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 PASTEUK. 
 
 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 filtration 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. 
 "^Tien, for example, the bacterium of splenic fever is 
 sown in the liquid, it assumes in a few hours a sm-- 
 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 attam 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 agam 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 PASTEUK. 
 
 death of the animal upon which it Hves and multipHes, 
 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 CHOLEEA. 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, m 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 
 stiU 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 PASTEUR 
 
 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 septicemia, and these three microbes do not 
 
FOWL CHOLERA. 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 PASTEUE. 
 
 THE ATTENUATED VIRUS, OR VACCINA- 
 TION OF VIRULENT DISEASES. 
 
 THE VACCINE OF FOWL CHOLEEA. 
 
 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 aU 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 7 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, OR 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 Tenner'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 
 cultm^e 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 PASTEUK. 
 
 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 bh'ds 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 ah' 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 spmts. But if this phenome- 
 non is extraordina.ry, 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 VIKUS, OE VACCINATION. 223 
 
 virulent virus — that, for instance, whicli 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 
 12 
 
224 LOUIS PASTEUK. 
 
 juxtaposition with the great fact of yaccination 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 fi"om 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, OR 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 
 
226 LOUIS PASTEUR. 
 
 microbe. A culture has a dm-ation of some clays ; in 
 twenty-four hours it is not terminated. The air which 
 comes in contact with it is then entirely emploj'ed 
 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 vhulence is so much weakened as to become 
 nU. 
 
 This very extraordinary fact is, then, established 
 that the virulence may be entnely 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. )\ray 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 then* 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 vh-us suggest inductions, awaken 
 ideas, and throw new lights upon a problem which, 
 until within these last few years, has remained so 
 obscure. Formerly it was believed that these vnuses 
 
THE ATTENUATED VIEUS, OE VACCINATION. 227 
 
 were morbid entities. A virus was a unity. This 
 opinion has still its declared upholders. Accordmg 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 vh'us wUl 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 vh'ulences. 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 vkus. 
 
 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 smaU-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, 
 
228 LOUIS PASTEUE. 
 
 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 proi)er 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 examj)le, of certain material 
 principles which the vital actions take a long time to 
 
THE ATTENTJATED VIEUS, OE VACCINATION. 229 
 
 restore to the systera, and wliich 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 sm-prise that the word vaccination, 
 hitherto exclusively reserved for Jenner's discovery, 
 was heard appHed 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 wiU consecrate, 
 as a homage to the merit and immense services 
 rendered to humanity by one of the greatest men of 
 England — Jenner.' 
 
 StUl, whUe 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 
 centm-y, medicine has not been able to derive anything 
 
230 LOUIS PASTEUE. 
 
 from it beyond its actual application, wliicli is the one 
 result achieved. 'Vaccination is yaccmation,' 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 vhus 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 aU 
 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.' 
 
THE VACCINE OF SPLENIC FEVER. 
 
 We have seen how the facts have been estabhshed 
 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 
 
232 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 possihihty 
 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 cm-e. 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 fom- 
 at a time, with the vu-ulent splenic fever vu'us. 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 weU 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 FEVER. 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. 
 Eoux. 
 
 Following the rigorous course of his deductions, 
 Pasteur naturally turned to the oxygen of the air in 
 his attempts to modify the virulence of the splenic 
 
234 LOUIS PASTEUR. 
 
 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 microscoi)ic 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 continumg 
 this first mode of generation, frequently exhibit, even 
 in the course of twenty-fom- 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 cohection 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 FEVEE. 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 vh'ulence, 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 microTje. 
 
 Pasteur and his two assistants gave themselves up 
 to this research. Days passed and experiments were 
 multiplied. Pasteur became more and more en- 
 
236 LOCIS PASTEUE. 
 
 grossed : he had, what his daughter called, ' the face 
 of an approachmg 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 FEVEE. 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 au- 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 vkulence 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 Eochette, came, in the name of the 
 Socitey, 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 Eoux, 
 
THE VACCINE OF SPLENIC FEVEK. 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 sheej) 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 Ul. 
 
 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,' 
 
240 LOUIS PASTEUE, 
 
 ' Take care,' they said to him, * you are commit- 
 ting yourself without possibihty 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. Eossignol, 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 FEVEE. 241 
 
 On May 31 very virulent inoculation was effected. 
 Veterinary 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 then* fii'st turn 
 of vh'ulent 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 meetmg was then ar- 
 ranged by Pasteur and all other persons present for 
 Thursday, June 2, thus altowing 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 then* 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 sweUings 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 ^he 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-Eort. 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 
 
244 LOUIS PASTEUK. 
 
 immunity generally lasted longer than a year. It is, 
 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 reahty 
 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 
 splenic 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, m order to 
 judge of the immunity of antisplenic vaccmation, we 
 must not lose sight of the formidable trial which 
 vaccinated animals have to undergo when moculated 
 with the most vu-ulent virus. What doctor would 
 dare to subject a vaccinated child to inoculation from 
 
THE VACCINE OP SPLENIC FEVER. 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 hfe. 
 
246 LOUIS PASTEUE. 
 
 THE RETURN 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 m 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 vhu- 
 lence — a deadly vhulence, 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 EETUEN TO YIEULEXCE. 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 vu-ulence 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 
 chmate, and gradually becoming acclimatised to the 
 last one. How great, then, must be the importance 
 of the medium of cultivation, with regard to the vnu- 
 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 killmg 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 
 13 
 
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 bu-d 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,' Pastern' 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 jjresent 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 VJHULENCE. 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 PASTEUU. 
 
 ETIOLOGY OF SPLENIC FEVER. 
 
 M. Pasteur had triumplied 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 Eussia, 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 FEVER. 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. 
 
 ' Reduce 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 PASTEUK. 
 
 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 obsciu'ity 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. 253 
 
 grew accustomed to the idea that the stricken animals 
 might have contracted the germs of the malady from 
 the outer world, without any spontaneous bhth, 
 strictly so called, of the disease. This opmion was 
 strengthened by a knowledge of the spores of the splenic 
 bacillus. Pasteur, aided by Messieurs Chamberland 
 and Eoux, 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 caUed spontaneous splenic fever. 
 The period of mcubation 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 pm'e 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 mortahty increased to 
 
254 LOUIS PASTEUE. 
 
 a 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 
 et Loire had been infected by germs or spores of the 
 splenic microbe contained in their food ; but the 
 question remained, Whence came these germs ? 
 
 Erom 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 mflation 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 FEVEE. 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 
 
258 LOUIS PASTEUR. 
 
 depths where they he buried, the terrible microbes. In 
 the tiny cyhnders 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 dhectly. 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 hght 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 sod, 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 Hable. 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 
 easUy 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 soU is only from 4 to 5 inches, superposed 
 upon chalk, the worms cannot hve ? 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, wUl abide in the depths of the 
 soil and remain harmless. Finally, it has been 
 
260 LOUIS PASTEUR. 
 
 proved that the countries subject to splenic fever have 
 an argillaeeous-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 
 thmg 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. 
 
2G2 LOUIS PASTEUE. 
 
 METHOD OF DISCUSSION AND 
 CONTRADICTIONS. 
 
 EvEEY 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 CONTEADICTIONS. 263 
 
 Loeffler, 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 roan to give way before an adversary, 
 he at last declared that the attacks of the German 
 savants must be repelled at BerUn 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 accejpted with deep and silent joy the 
 management of an experiment that was to test a 
 
264 LOUIS PASTEUE 
 
 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 Pastern- 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 Yirchow. 
 
 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 CONTEADICTIONS. 265 
 
 Geneva. Thither went Pasteur, hoping to meet Dr. 
 Koch at the sittings ; and he was not disai^pointed. 
 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 PASTEUE. 
 
 hamper it. In scientific discussions, it is not as in 
 politics,' he added with a smUe, ' 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 j^ast 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 CONTEADICTIONS. 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- 
 verhal 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. 269 
 
 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 an,' 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 vibratmg 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. Xo 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 agricultm-e that, as the learned 
 Enghsh professor Huxley has truly said, ' Pasteur's 
 discoveries suffice, of themselves, to cover the war 
 
270 LOUIS PASTEUE. 
 
 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 ! ' 
 
THE LABORATORY OF THE ECOLE 
 NORMALE. 
 
 VARIOUS STUDIES. HYDEOPHOBIA. 
 
 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 Eollin 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 retamed, in the 
 14 
 
272 LOUIS PASTEUK. 
 
 basement of his laboratory in tlie Eue d'Ulm, a whole 
 population of animals mider experiment. Isolated in 
 round cages which impart some sense of security, are 
 the rabid dogs ; some attacked with furious madness, 
 biting then- 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 ftlarm 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 m 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 LABOKATORY OF THE ECOLE XOEMAT.E. 273 
 
 and true light ; that of the mterest 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 Tip 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 vh'us 
 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 
 
274 LOUIS PASTEUE. 
 
 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 bu'd 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 fm-iously 
 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 retm-n of a ship which was to 
 bring back some passengers attacked with yellow 
 
THE LABOEATOEY OF THE ECOLE KOEMALE 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 httle 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 
 apphed 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. 
 
276 LOUIS PASTEUR. 
 
 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 j)receded the 
 formation of the pus, were sown in a sterilised infusion, 
 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 microscoiDic 
 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 LABOEATOEY OF THE ECOLE NOEMALE. 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 smaU 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 PASTEUK, 
 
 find some fruitful in the little organism of the 
 boils.' 
 
 But whilst Dr. Maurice Eaynaud 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 LABOEATOEY OF THE ECOLE NOEJIALE. 279 
 
 like that of boils, in pairs of two or four, and also in 
 parcels, some with a clearly defined 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 hom-s 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. 
 
 I. 
 
 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 PASTEUE. 
 
 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 w^hich 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 h-esh 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, theother 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 
 all 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, w^hich, at the ordinary tem- 
 perature, contain from thirty to forty grammes of acid 
 to one litre of water. 
 
 'Would it not be very useful,' said Pastem' 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 LABORATOEY OF THE ECOLE NOEilALE. 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 aU the germs of common organisms. 
 
 I 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 
 desh-e 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 PASTEUK. 
 
 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- 
 peruuents 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 
 precedmg cultivation bemg 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. Loh, 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 LABOEATOEY OF THE ECOLE N0E5IALE. 285 
 
 After having had recourse to the oxygen of the air to 
 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 A^accinated pig was attacked. ' They are all 
 flourishing,' wrote M. Maucuer. An address of thanks 
 was sent to Pasteur by the municij^al council of 
 Bollene. 
 
 But, notwithstanding these happy results, the 
 question of the application of vaccines to different 
 breeds requhes 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 is 
 capable of being made permanent by culture. A 
 
286 I,OUIS 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 sj)lenic 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 LABOEATOKY OF THE ECOLE NORMALE. 287 
 
 * The Academy remembers, without doubt,' said 
 Pasteur in a recent communication, ' that, some time 
 ago, we discovered a microbe virus in the saHva 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 vhulence 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. Babbits 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. 
 
TFTE LABORATOKY OF THE ECOLE NOEMALE. 289 
 
 * Wtien the virus is inoculated from rabbit to 
 rabbit, the microbe acchmatises 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 vh'ulence has been progressively diminishing 
 from the first rabbit to the following ones. Yery 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 Pfydrophobia. 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 PASTEUE. 
 
 which an obscure problem had for him, he felt that if 
 he succeeded in discovering the jjrobably 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 LABOEATORY OF THE ECOLE NORMALE. 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 thhst, 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 dehrium 
 began, a frightful delirium. The frothy matters 
 which filled his throat suffocated him. 
 
 Four hours after his death, the mucus 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 PASTEUE. 
 
 tion of hvclrophobia ? 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 j\I. 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 beheve, 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. 
 Mamice Piaynaud 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 LABOEATOKY OF THE ECOLE KOEMALE. 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 vhus. 
 
 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 degress 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 LABOEATOKY OF THE ECOLE NOEMALE. 295 
 
 Impatient "with, the length of time required for 
 the incubation of the disease, and with the obhgation 
 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 vh'ulence 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 vu'ulence in 
 15 
 
296 LOUIS PASTEUR. 
 
 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 LABORATOEY OF THE ECOLE NORMALE. 297 
 
 for communicating tlie 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. 
 
298 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 LAEORATOEY OP THE ECOLE NORMALE. 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 "vyith 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 PASTEUE. 
 
 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 
 spasm, 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. 
 
LOUIS PASTEUR: 
 
 HIS LIFE AND LABORS. 
 
 BY HIS SON-IN-LAW. 
 
 Translated from the French by Lady Claud Hamilton. With ks 
 Introduction by Professor Tyndall. 
 
 i2mo, cloth, $1.25. 
 
 "Never was man of science more fortunate in his 'biographer. The hook lias 
 the interest of a novel joined to that of heroic biography. The translation is 
 excellent."— iV^ Y. Commercial Advertiser. 
 
 " The hook as a whole is much more a sketch of the man's work than of the 
 man himself; and the work is great work." — N. Y. Evening Fost, 
 
 " Pasteur's discoveries have so often heen almost sensational in their brilliancy 
 and unexpectedness, and have so frequently ministered to the comfort, health, 
 and material prosperity of mankind, that the story of them has all the interest of 
 a well-wrought Action."— iVeo; Ywk Examiner. 
 
 " The results achieved by Pasteur are so far in advance of those ohtained hy 
 any of his contemporaries that he may be safely placed where the last century 
 placed Newton." — Springfield Republican. 
 
 " To give a complete description of the contents of the book would be futile 
 but the ' Studies on Wine and IJeer,' ' Attenuated Virus,' the ' Etiology of Splenic 
 Fever.' and descriptions of the laboratory of the celebrated Normal School and 
 experiments in hydrophobia, will probably draw most of the reader's attention." 
 — New Haven News. 
 
 "The picture of Pasteur leaning over the foaming head o( a mad dog held 
 motionless by attendants and suffocatins' with fury, and at a distance of a finger's 
 length Buct^ing up into a narrow tube some drops of the saliva, is truthfully illus- 
 trative of his earnest and fearless love of science throughout his life. Hydropho- 
 bia has been his latest study. As regards the attenuation of the rabid virus, and 
 the rendering of an animal by inoculation proof against attack, the success of 
 M. Pasteur is assured. The volume describes in detail and with clearness the 
 labors of a bold pioneer in scientific experiment, whose contributions to scientific 
 knowledge and to the happiness of humanity are among the most valuable of his 
 period. The narrative of what he has done and is doing is a most important 
 one."— iJostoft Globe. 
 
 " The discovery of corpuscles which produced a disease from which all the 
 silk-worms in France were dying, and of the means of preventing their spread, 
 made Louis Pasteur famous in France twenty years ago. His more recent dis- 
 coveries of disease microbes and of the power to render contagious diseases 
 harmless by inoculation have made his name known from one end of the earth to 
 the other." — Philadelphia Inquirer. 
 
 For sale by all booksellers ; or sent by mail, post-paid, on receipt of price. 
 
 New York : D. APPLETON & CO., Publishers, 1, 3, & 5 Bond Street. 
 
THE STORY OF MY LIFE. 
 
 By the late J. Marion Sims, M. D. Edited by his Son, H. Marion-Sius, 
 M.D. 12mo, cloth, 4'72 pages. |1.50. 
 
 "Marion Sims, by himself and through others, has restored to society and 
 to happiness an ever-increasing multitude of sufferers, condemned, before he 
 opened the way of escape, to life-long wretchedness. For himself he achieved 
 such renovru that his name is a household word in medical circles the world 
 over. But the story is more than an autobiography : it not merely illustrates the 
 evolution of a South Carolina country lad into one of the most useful and con- 
 spicuous of modern benefactors ; it Is local history interpreting rural life in 
 that aection fifty years ago." — New York Evening Post. 
 
 " The book opens with a very interesting introduction, in which Judge T. J. 
 Mackey pays a deserved tribute to the distinguished surireon, and recapitulates 
 the aciiievements upon which his professional fame rests, and which have won 
 him recognition in Europe and America as the foremost clinical surgeon of the 
 age. Dr. Sims was born in Lancaster County, S. C, and though the greater part of 
 his life was spent away from his native State, South Carolinians have a right to 
 feel a personal pride in the reputation he won." — Charleston Ntws and Courier, 
 
 " The claim of Dr. Sims to the regard of posterity rests on a number of pro- 
 fessional achievements conferring honor on both hindeelf and his country. Firft, 
 he invented the silver suture and applied it successfnlly to cases of fistula, until 
 then deemed incurable. Second, he invented what ie known as the ' Sims Spec- 
 ulum' — the most effective now known. Third, he made an exposition of the 
 pathology and true method of trismus nascentivm, or the lock-jaw of infants. 
 Pourth,Tie was the founder and organizer of the Woman's Hospital of the State 
 of New York, the first institution ever dedicated exclusively to the cure of the 
 diseases of women. Fifth, he made valuable contributions to medical literature. 
 The story of a life so full of usefulness to his fellows will have a peimanent value, 
 and will be widely read by all who admire the benefactors of the human race." — 
 T/vr/ Daily Evening Times. 
 
 " The medical profession will find a peculiar interest in this volume, in which 
 the great physician tells the stoiy of his career, and of those brilliant discoveries 
 and inventions which have given renown not only to him, but to the entire body 
 of American medical science. In his special departments be enlarged the scope 
 of surgery for the whole world, and it is not too much to say that his name will 
 stand in the completed history of the science as one of its illustrious creators. He 
 was not less distinguished for the simple virtues and noble heroism of his char- 
 acter in private life, than for his successes in his profession, and this testament 
 from his hand will commend him to the love and reverence of thousands who 
 have only known him hitherto through the reports of fame."— iV. T. Home Journal. 
 
 "The late Dr. Sims probably obtained a wider reputation than any other 
 American physician. His brilliant discovery in a highly important but obscure 
 department of surgery won the admiration of his profession in the New and Old 
 Worlds. His fame culminated in this country as far back as 1855, when the Wom- 
 an's Hospital was established in New York for the sole purpose of curing by 
 his method a trouble that had previously been deemed incurable. The leaders in 
 the New York fashionable society of that day took charge of this truly philan- 
 thropic work. They were assisted in it by our most distinguished local physi- 
 cians and surgeons, who freely testified to the extraordinary merit of Dr. Sims's 
 discovery. B'or nearly thirty years this institution has been one of the crowning 
 mercies of New York. Dr. Sims in this work tells the story of his life with the 
 utmost fullness and franknesii:. Aside from his claims on the gratitude of woman- 
 kind, the doctor had a history well worth telling. In Paris, London, and other 
 capitals of Europe, he was thrown into much brilliant society, and of this he jots 
 down his recollections in a fresh and amusing manner."— iVew York Journal of 
 Commerce. 
 
 For sale by all booksellers ; or will be sent by mail, post-paid, on receipt 
 of price. 
 
 New, York: D. APPLETON & CO., Publishers, 1, 3, & 5 Bond Street. 
 
MAXIMS OF PUBLIC HEALTH. 
 
 By 0. W. Wight, M. D., of the Detroit Board of Health. 16mo, cloth, 
 
 Y5 cents. 
 
 •' The appearance of this hand-hook is most timely. There is a vagae appre- 
 hension that the cholera may visit the dnited States next year. Everybody 
 wants to know virbat to do for the exclusion or limitation of the dread disease. 
 Dr. O. W. Wight, to whom we owe these 'Maxims of Public Health,' speaks 
 with the voice of authority. He has been for six years Health Officer of Detroit, 
 !ind has made epidemics the subject of patient and earnest study. Here we have 
 the fruits of all his experience and observation. His book ought to be placed in 
 the hands of every person connected in any way with health boards in all parts 
 of the country. It is invaluable for instant reference in an emeraency. Dr. 
 Wight proves his competency to speak cm this subject by the emphasis be puts 
 on cleanliness of houses and streets as the best safeguard against pestilence." — 
 Mw York Journal of Commerce. 
 
 " Dr. Wight is to be commended, not only for reiterating the dangers to which 
 we are subject, both in city and country, from unsanitary surroundings, but 
 because he has clothed his thoughts in virile, understandable English. He has 
 the ordinary scientific view of filth as the breeder of certain contagious diseases 
 — scarlet fever, typhoid fever, diphtheria and the like — but has a new idea con- 
 cerning the removal of sewage before it putrefies. As he puts it in the preface, 
 'the only way to get rid of sewer-gas is not to make any.' It is a pleasure to 
 read his thoughts ; they can not be other than a great boon to the unprofessional 
 man, for whom they are specially written." — RartJ'ord Evening Fost. 
 
 "The intelligent householder who has no time, perhaps no inclination, for 
 systematic studies, may reiid these maxims with a quick comprehension of their 
 import, and find hints that will save himself and his loved ones unspeakable 
 pain and sorrow. To say nothing of his success as a medical practitioner. Dr. 
 Wight gives in this valuable book the result of six years of personal experience 
 in sanitary administration. We heartily commend it to the careful reading of 
 all who would be prepared to ward oflf any epidemic that should make its appear- 
 ance in their midst, or who would have everything about their premises of the 
 most healthful character."— .Boston. Home Journal. 
 
 "Dr. Wight's heart is at his pen's point in every page of his book, and he is 
 as exhaustive upon every phase of human life and suflering and exposure and 
 economy, as he is on the school."— 5<. Paul Dispatch. 
 
 "A little volume which condenses within less than two hundred pages a vast 
 amount of sanitary science. . . . The book is evidently the result of long and 
 close attention to the subject, and, being designed for the general reader, it gives 
 the results of investigation and experiment without burdenins them with de- 
 tails of the processes by which they have been reached. It is a book which should 
 be studied by all." — Chicago Daily Times. 
 
 " This is a timely and most instructive as well as interesting series of para- 
 graphs on sanitary subjects, which ought to be read in every household and 
 board of health." — Newark Daily Adwriiser. 
 
 "He plunges into the subject of city drainage, handling the topic with such 
 skill and precision as prove him a past master of hygienic science. Every 
 possible phase of house, stable, and city drainage, and sanitation, is explained 
 and discussed." — Detroit Evening News. 
 
 For sale by all booksellers ; or will be sent by mail, post-paid, on receipt 
 of price. 
 
 New York: D. APPLETON & CO., PubliBhers, 1, 3, & 5 Bond Street. 
 
WOMEN, PLUMBERS, AND DOCTORS; 
 
 OR, HOUSEHOLD SANITATION. 
 BY MRS. H. M. PLUNKETT. 
 
 Showing that, if women and plumbers do their whole sanitary 
 
 duty, there will ie comparatively little occasion for 
 
 the services of the doctors. 
 
 Witli 50 Illustrations - - - 12mo, cloth, $1.25. 
 
 CHAPTER-EEA DS. 
 HTGiEjno HoTTSES. Sewage and Pl.rMBrSTG. 
 
 Undee the Hoobb. Sewek Gas and Germs. 
 
 Abeangement of the House. Overlooked Channels of Infection. 
 
 Lighting the House. Oue Neiguboe's Premises. 
 
 Wholesome Watee. Public Sanitation. 
 
 "Here is a really profound and thorough investigation into the causes of half the 
 diseases that afflict humanity. If dwellings were built in the right places, properly 
 constructed and furnished, and then carefully looked after, sickness would rarely occur 
 in such houses. Mrs. Plunkett cites numerous facts from the experience of herself 
 and others to prove all she says. She tells many touching stories to illustrate the 
 fatal results of ignorance and neglect of the laws of health in American homes. The 
 book is very interesting, aside from its instructive and useful character. It is full of 
 pictures showing the contrasts of good and bad plumbing, complete and defective 
 drainage, etc. The reading of practical books like this one will do much to educate 
 our people in the art of making homes healthy and happy." — Jfew York Journal of 
 Commerce. 
 
 " After a few pages on sanit-ation in general. Mrs. Plunkett describes the dangers 
 •which lurk in wet house-sites and inadequate foundations, and then proceeds with the 
 arrangement of the house for securing sufficient warmth, ventilation, and sunshine. 
 The next chapter deals with lighting, and contains many facts in relation to dan- 
 gerous burning-oils that every housewife should thoroughly know. Various ways in 
 which water may become unwholesome are told, with directions for tests and measures 
 of protection. The requirements of a good system of plumbing are stated, examples 
 of defective work are given, and some explanation of the nature of sewer-gas and 
 disease-germs is added. As many eminent physicians have declared that cholera will 
 certainly come to America in 1835, a memorandum of the Kew Tork State Board ot 
 Health relating to the prevention of the disease has been introduced, together with 
 directions for home treatment, including recipes for medicines. The book, though 
 aiming especially to interest women, is addressed to all readers who desire a popular 
 and practical presentation of this important subject; quotations from the writings of 
 able physicians and sanitarians have been freely used, and evidently care has been 
 taken to make a useful and reliable book." — The Popular Science Monthly. 
 
 "Mrs. H. M. Plunkett has written a book that will prove a blessing in thousands of 
 households, if only its important lessons are heeded. She clearly shows why women 
 should understand the details as well as the theory of sanitation, and furnishes all 
 information to enable them to possess such an understanding." — Boston Honie Jour- 
 nal. 
 
 "The work is well written, and the diagrams showing the perfect and imperfect 
 work are simple and easily understood ; it is well worth perusal by every father, and 
 more particularly by every mother of a family, showing, as it does, where most of the 
 seeds of disease germinate." — Rochester Post and Express. 
 
 For scHe by all booksellers ; or sent by mail, post-paid, on receipt of price. 
 New York: D. APPLETON & CO., Publishers, 1, 3, & 5 Bond Street. 
 
GEORGE J. ROMANES'S WORKS. 
 
 Jelly-Fish, Star-Fish, and Sea-Urchins. Being a Ee- 
 
 searcti on Primitive Nervous Systems. 12mo. Cloth, $1.75. 
 
 "Although I have throughont kept in view the requirements of a general 
 reader, I have also sought to render the book of service to the v^orking physi- 
 ologist, by bringing together in one consecutive account all the more important 
 observations and results which have been yielded by this research." — Extract 
 from Preface. 
 
 " A profound research into the laws of primitive nervous systems conducted 
 by one of the ablest English investigators. Mr. Komanes set up a tent on the 
 beach and examined his beautiful pets for six summers in succession. Such 
 patieut and loving work has borne its fruits in a monograph which leaves 
 nothing to be said about jelly-fish, star-fish, and sea-urchins. Every one who 
 has studied the lowest forms of life on the sea-shore admires these objects. But 
 few have any idea of the exquisite dehcacy of their structure and their nice 
 adaptation to their place in nature. Mr. Romanes brings out the subtile beauties 
 of the rudimentary organisms, and shows the resemblances they bear to the 
 higher types of creation. His explanations are made more clear by a large 
 number of illustrations. While the book is well adapted for popular reading it 
 is of special value to working physiologists. "— A'ew York Journal of Commerce. 
 
 "Six years have been consumed in these investigations and experiments, and 
 the result is a condensed statement of probably all that is known at present con- 
 cerning these curious and beautiful fishes." — i\'ew York Evening Telegram. 
 
 " A most admirable treatise on primitive nervous systems. The subject-matter 
 is full of original investigations and experiments upon the animals mentioned as 
 types of the lowest nervous developments. " — Boston Commercial Bulletin. 
 
 "Mr. George J. Romanes has already established a reputation as an exact and 
 comprehensive naturalist, which his later work, 'Jelly-Fish, Star-Fish, and Sea- 
 Urchins,' fully confirms. These marine animals are well known upon our coasts, 
 and always interest the on-lookers. In this volume (one of the 'International 
 Scientific Series') we have the whole story of their formation, existence, nervous 
 system, etc., made most interesting by the simple and non-professional manner 
 of treating the subject. Illustrations aid the text, and the professional student, 
 the naturalist, all lovers of the rocks, woods, and shore, as well as the general 
 reader, will find instruction as weU as delight in the narrative."— J5o«io« Com- 
 monwealth. 
 
 Animal Intelligence. i2mo; Clotb, $1.75. 
 
 "A collection of facts which, though it may merely amuse the unscientific 
 reader, will be a real boon to the student of comparative psychology, for this is 
 the first attempt to present systematically the well-assured results of observation 
 on the mental life of &mma\a."'— Saturday Eeview. 
 
 Mental Evolution in Animals. With a Posthumous Es- 
 say on Instinct, by Ohaeles Daewin. 12mo. Clotb, $2.00, 
 
 "Mr. Romanes has followed up his careflil enumeration of the facts of 'Ani- 
 mal Intelligence.' contributed to the ' International Scientific Series,' with a 
 work dealing with the successive stages at which the various mental phenomena 
 appear in the scale of life. The present installment displays the same evidence 
 of industry in collecting facts and caution in co-ordinating them by theory as the 
 former."— 2%e Athenoeum. 
 
 New York: D. APPLETOX & CO., 1, 3, & 5 Bond Street. 
 
Origin of Cultivated Plants, 
 
 By ALPH0N3E DE CANDOLLE. 
 121110. Cloth, $2.00. 
 
 "The copious and learned work of Alpbonse de Candolle on the 'Orisin of 
 Cultivated Plants' appears in a translation as volume forty-eisfht of the 'Inter- 
 national Scientific Series.' Any extended review of this book would be outof 
 place here, for it is crammed with interesting and curious facts. At the begin- 
 nln? of the century the orijrin of most of our cultivated species was unknown. 
 It now requires more than four hundred closely printed paees to sum up what 
 is known or conjectured of this matter. Among his conclusions M. Candolle 
 makeg this interesting statement: 'lu the history of cultivated plants I have 
 noticed no trace of communication between the peoples of the Old and New 
 Worlds before the discovery of America by Columbus.' Kot only is this book 
 readable, but it is of great value for reference." — New York Herald. 
 
 "If general and lasting usefulness is to be accepted as the test of meritorious 
 achievement, it might do us no harm to remember that within the last two 
 thousand years man has not won from nature by discovery and cultivation a 
 single species of food staple comparable with wheat, rice maize, the potato, and 
 the banana, some of which invaluable conquests can indeed be proved to have been 
 made more than forty centuries ago. This is one of the suggestive facts con- 
 tributed by botany to the history of the birthplace and evolution of civilization, 
 and which are discussed in the light of the ripest and most accurate investigation 
 by the well-known Genevan scientist, Alphonse de Candolle. in the 'Origin of 
 Cultivated Plants.' Of the one hundred and twenty to one hundred and forty 
 thousand species in the vegetable kingdom, man has detected properties suffi- 
 ciently precious to make it worth while to cultivate the plants on a large scale, 
 and for use in less than three hundred instances." — Kew York Sun. 
 
 "Not another man in the world could have written the book. and. considering 
 both its intrinsic merits and the eminence of its author, it must long remain the 
 foremost authority in this curious branch of science. Of the 247 plants here 
 enumerated. 199 are from the Old World, 45 are American, and -3 unknown. Of 
 these only 67 are of modern cultivation. Curiously, however, the United States, 
 notwithstanding its extent and fertilitv, makes only the pitiful showing of 
 gourds and the Jerusalem artichoke." — Boston Literary World. 
 
 " The volume, though not large, is evidently the result of great study and 
 research. Botanists in all parts of the world, travelers, herbaria, works on botany, 
 history, archaeology, and philology, have been all called upon to contribute to 
 the results. The author justly remarks in his preface that 'the knowledge of 
 the origin of cultivated plantsis interesting to agriculturists, to botanists, and 
 even to historians and philosophers conrerned with the dawnings of civiliza- 
 tion.' " — Albany Cultivator and Country Gentleman. 
 
 " In a word, all that can be recorded of the plant kingdom is given in the four 
 hundred and fifty and more pages of the volume, and a gond index aids materially 
 the readers. AH flower-lovers can find substantial information about their 
 favorites in the work."— £o5to« Commonwealth. 
 
 "It is an exhaustive treatise on the habitat and origin of all the useful plants 
 known to medicine, cookery, and science. One is here informed that the turnips 
 come from Siberia, that the strawberry grows wild in Europe from Lapland to 
 the isles of Madeira and Greece gooseberries come from the Caucasus, and wheat 
 from the region of the Euphrates. Rice was known 2.800 years b. c. in a cere- 
 mony in whicli the Emperor of China plays a conspicuous part." — Cincinnati 
 Enquirer. 
 
 New York : D. APPLETON & CO., 1, 3, & 5 Bond Street.