III.
We have now arrived at the end of this long investigation. All the obscurity which enveloped the origin of the diseases of silkworms had now been dispelled. Pasteur had arrived at such accurate knowledge both of the causes of the evil and their different manifestations, that he was able to produce at will either pébrine 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 explorations for procuring non-infected eggs was both insufficient and precarious. It simply amounted to going very far to seek, and paying very dear, for seed which could not be relied on with certainty. The prosperity of the silkworm culture could only be secured by measures capable of restoring to the native eggs their pristine qualities.
The results obtained by Pasteur were sufficient to solve this problem. The struggle against flacherie was easy, but there remained the struggle against pébrine. To triumph over this disease, which was so threatening, Pasteur devised a series of observations as simple as they were ingenious.
Here is a crop which has perfectly succeeded. The moultings, and the climbing upon the heather, are all that could be desired. The cocoons are finished, and the appearance of the moths alone is waited for. They arrive, and they pair. Then begins the work of the cultivator, who is careful about the production of his eggs. He separates the couples at the end of the day; laying each female moth by itself on a little linen cloth suspended horizontally. The females lay their eggs. After the laying, he takes each female in turn and secures her by a pin passed through the wings to a folded corner of the little cloth, where are grouped some hundreds of eggs which she has laid. The male moth also might be pinned in another corner of the cloth, but the examination of the male is useless, as it has been found that he does not communicate the pébrine. The female moth, after having been desiccated by free contact with the air, is examined at leisure, it may be even in the autumn or winter. Nothing 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 ventured to hope that he should be able to find the means 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 Ardèche, in Gard, in the Drôme, and in other countries, may be met with everywhere, at the time of the cultivation, workshops where hundreds of women and young girls are occupied, with a remarkable division of labour and under the strictest supervision of skilful overseers, in pounding the moths, in examining them microscopically, and in sorting and classifying the little cloths upon which the eggs are deposited.
But if Pasteur had brought back wealth to ruined countries, if he had returned to Paris happy in the victory he had gained, he had also undergone such fatigues, and had so overstrained himself in the use of the microscope while absorbed in his daily and varied experiments, that in October 1868 he was struck with paralysis of one side. Seeing, as he thought, death approaching, he dictated to his wife a last note on the studies which he had so much at heart. This note was communicated to the Academy of Sciences eight days after this terrible trial.
A soul like his, possessing so great a mastery over the body, ended by triumphing over the affliction. Paralysed on the left side, Pasteur never recovered the use of his limbs. To this day, sixteen years after the attack, he limps like a wounded man. But what stages had this wounded man yet to travel over, what triumphs were yet in store for him!
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 future labours, he entered into these thoughts and appeared to add faith to their hopes. He finished by sharing them.
In January 1869, although it was still impossible for him to drag himself about his room, he was so much excited by the contradictions that his system of culture had aroused that he wished to start again for Alais. 'Aided by the method of artificial cultivation,' he remarked, 'we shall soon annihilate these latest oppositions. There is here both a scientific principle and an element of national wealth.'
His wish could not be opposed, but a terrible and anxious journey it was! At some leagues from Alais, at a place called Saint Hippolyte-du-Fort, where the earliest experiments were made, Pasteur stopped. He installed himself—we might rather say he encamped—with his family and his assistants, in a more than humble lodging, one of those miserable, cold, paved houses of the rural districts. Seated in his arm-chair, Pasteur directed the experiments, and verified the observations which he had made the year before. Each of his predictions as to the destiny of the different groups of worms was fulfilled to the smallest detail. In the following spring he left for Alais, where he followed in all their phases, from the egg up to the cocoon, the cultivations there undertaken, and he had the happiness of proving once more the certainty of his method.
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 net 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 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 withdraw 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.
STUDIES ON BEER.
The war was over. Little by little the life of the country was resumed, and with returning hope the desire and necessity for renewed work. After two years of infirmity, Pasteur at length began to feel the recovery of health. It was like a slow and gentle renewal of all things. He wished to return as soon as possible to his laboratory in Paris to put into execution 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 accepted it. Eager to commence an investigation which would bring him again to the study of fermentation, he attacked the diseases of beer. But it was not only for the purpose of creating a new link between these researches and his former ones that he occupied himself with this subject, he was also influenced by a somewhat patriotic idea. He dreamt of success in an industry in which Germany is superior to France. He hoped by means of scientific principles, by which commerce 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 consumed 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 fermentation sets in. The cooling ought to be performed rapidly. While the wort is at a high temperature there is nothing to fear, it remains sound; but under 70° Centigrade, and particularly between 25° and 35°, it is easily attacked by injurious ferments—acetic, lactic, or butyric. After the wort is cooled, a little of the yeast proceeding from a former fermentation 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 without yeast—to so-called spontaneous fermentation—this would hardly ever be purely alcoholic, as in the must of grapes, which is protected by its acidity. Most frequently, instead of beer, an acid or putrid liquid would be obtained. Divers fermentations would simultaneously take place in it. When the wort has fermented and the beer is made, there is still the fear of its rapid deterioration, which necessitates its being quickly consumed. This condition is sometimes disastrous to those employed in the beer trade; and the improvements in the manufacture 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 constant 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 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 fermentation lasts for three or four days, then the beer is made and has become clear; the bungs are fixed in the barrels, and they are sent direct to the retail dealer or to the consumer. During the transit, a certain quantity of yeast, fallen to the bottom of the casks, thickens the beer, but a few days of repose suffice to make it again clear and fit to drink, or to be bottled.
This system of 'high' fermentation (so called because it begins at a temperature of 18° to 20°, and is raised one or two degrees higher by the act of fermentation 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, after it has been cooled, is passed into open wooden tuns, and the working of the yeast takes place at a temperature 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 sometimes 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 temperature 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 beginning 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 bière de garde, beer for keeping, 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 fermentation 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 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 substances used in the manufacture. 'By the expression diseases of wort and of beer, I mean,' said Pasteur, 'those serious alterations which affect the quality of these liquids so as to render them disagreeable to the taste, especially when they have been kept for some time, and which cause the beer to be described as sharp, sourish, turned, ropy, putrid.' The wort of beer, after it has been raised to the boiling heat, may, as Pasteur's experiments testify, be preserved indefinitely, even in the highest atmospheric temperatures, when in contact with air free from the germs of the lower microscopic organisms. The must, leavened by the addition of pure yeast, kept free from foreign organisms, 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 preservative? But beer is a drink necessarily charged with carbonic acid, and the application of heat to considerable 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 Pasteurised 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, constructed 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 pure as possible. At the Exhibition of Amsterdam there might be seen bottles half full, containing a perfectly clear beer, which had been tapped from the time of opening of the Exhibition. This was French beer, manufactured according to Pasteur's principles, by a great brewer of Marseilles, M. Velten. The happy effect of these studies is universally recognised. At Copenhagen, M. Jacobsen has had a bust of Pasteur, by Paul Dubois, placed in the salle d'honneur of his celebrated laboratory.
In terminating his Studies on Beer, Pasteur recalled to mind the principles which for twenty years had directed his labours, the resources and applications of which appeared to him unlimited. 'The etiology of contagious diseases,' he wrote with a scientific certainty of conviction, 'is on the eve of having unexpected light shed upon it.'
VIRULENT DISEASES.
SPLENIC FEVER (CHARBON)—SEPTICÆMIA.
'He that thoroughly understands the nature of ferments and fermentations,' said the physicist Robert 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 understood without an insight into the doctrine of fermentations.'
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 fermentation. When Pasteur in 1856 began his labours on these subjects, the ideas of Liebig were everywhere revived. Like the ferments, so the viruses and processes of disease were considered as the results of atomic motions proper to substances in course of molecular change, and able to communicate themselves to the diverse constituents of the living body.
The researches of Pasteur on the part played by microscopic organisms in fermentation, changed the course of these ideas. The ancient medical theory of parasites and living contagia was revived. A German Professor, Dr. Traube, in 1864, put forward, in one of his clinical lectures, a new doctrine of the ammoniacal fermentation of urine.
'For a long period,' he said, 'the mucus of the bladder was regarded as the agent of the alkaline decomposition of urine. It was supposed that, in consequence of the distension produced by the retention of the liquid, the irritated bladder produced a larger quantity of mucus, and this mucus was regarded as the ferment which brought about the decomposition of urea, by an innate chemical force. This opinion (which was that of Liebig) cannot 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 quâ non of the process.' And Dr. Traube, citing some facts which confirmed the doctrine of Pasteur, concluded thus: 'Notwithstanding the long retention of the urine, its alkaline fermentation 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.
The opposite doctrines of Liebig and Pasteur are here brought into clear juxtaposition; and thus was their mutual and reciprocal influence established in dealing with the etiology of one of the most serious diseases of the bladder. So far back as 1862, Pasteur, in his memoir on spontaneous generation, had announced, contrary to all the notions then held, that whenever urine becomes ammoniacal, a little microscopic fungus is the cause of this alteration. Later on he established that in affections of the bladder ammoniacal urine was never found without the presence 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 ammoniacal ferment, advised Dr. Guyon, Clinical Professor of Urinary Diseases in the Faculty of Paris, to combat the dangerous ammoniacal fermentation by injection of boracic acid into the bladder. The celebrated surgeon hastened to follow this advice, and with the most happy results. While attributing to Pasteur the honour of this discovery, M. Guyon, in one of his lectures, said:—
'Boracic acid has this immense advantage, that it can be applied in large doses—3 to 4 per cent.—without causing the slightest pain. It has therefore become, in our practice, the agent continually and successfully used for injections. I also have recourse to a solution of boracic acid to produce large evacuations after the operation of breaking up stones in the bladder (lithotrity). I never omit to use this antiseptic agent in operations where breaking up is required, and I never wash the bladders of lithotritised patients with any other substance. I have also had good results from copiously washing the bladders and the wounds of patients on whom lithotomy has been performed with boracic acid. I always finish the operation by prolonged irrigations with a solution of from 3 to 4 per cent.'
It was not only into France and Germany that Pasteur's ideas penetrated; in England, surgery borrowed from Pasteur's researches important therapeutic applications. In 1865 Dr. Lister began in Edinburgh the brilliant series of his triumphs in surgery by the application of his antiseptic method, now universally adopted. In the month of February 1874 in a letter which does honour to the sincerity and modesty of the great English surgeon, he wrote to Pasteur as follows:—
'It gives me pleasure to think that you will read with some interest what I have written about an organism which you were the first to study in your memoir on lactic fermentation. I do not know whether you read the 'British Medical Journal;' if so, you will from time to time have seen accounts of the antiseptic system which for the last nine years I have been trying to bring to perfection. Allow me to take this opportunity of sending you my most cordial thanks, for having, by your brilliant researches, demonstrated 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 direction. 'I am neither doctor nor surgeon,' he used to repeat with modest self-distrust. But the moment came when, notwithstanding all his scruples, he could no longer be content himself to play the part of a simple spectator of the labours started by his studies on fermentation, on spontaneous generation, and on the diseases of wines and beer. The hopes to which his methods gave rise, the eulogies of which they were the object, obliged him to go forward. In February 1876 Tyndall wrote to him thus:—
'In taking up your researches relating to infusorial organisms, I have had occasion to refresh my memory of your labours; they have revived in me all the admiration which I felt on first reading them. It is my intention to follow up these researches until I shall have dissipated every doubt that has been raised as to the unassailable exactitude of your conclusions.
'For the first time in the history of science we are able to entertain the sure and certain hope that, in relation to epidemic diseases, medicine will soon be delivered from empiricism, and placed upon a real scientific basis. When this great day shall come, humanity will recognise that it is to you the greatest part of its gratitude is due.'
Pasteur approached the study of viruses by seeking to penetrate into all the causes of the terrible malady called splenic fever (charbon, Germ. Milzbrand). Each year this disease decimates the flocks not only in France but in Spain, in Italy, in Russia, where it is called the Siberian plague, and in Egypt, where it is supposed to date back to the ten plagues of Moses. Hungary and Brazil pay it a formidable yearly tribute; and to come back to France, the losses have amounted in certain years to from fifteen to twenty millions of francs. For centuries the cause of this pest has eluded all research; and further, as the malady did not always exhibit the same symptoms, but varied according to the kind of animal that was smitten by it, the disease was supposed to vary with the species that was attacked by it. The splenic fever of the horse was distinct from that of the cow; the splenic fever of horse and cow were again different from that of the sheep. In the latter, splenic fever was called 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-Loir made a great number of inoculations, applied other tests, and proved that the splenic fever of the sheep is communicable to other sheep, to the horse, to the cow, and to the rabbit; that the splenic fever of the horse is communicable to the horse and to the sheep; that the splenic fever of the cow is communicable to the sheep, to the horse, and to the rabbit. As for the malignant pustule in man, no doubt remained that it must arise from the same cause as splenic fever in animals. What class of men is it that the malignant pustule most frequently attacks? Shepherds, cowherds, cattle breeders, farm servants, dealers in hides, tanners, wool cleaners, knackers, butchers—all who derive their living from domestic animals. In handling contaminated 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 neighbourhood of herds smitten with splenic fever. There are also certain flies which transport the virus. Suppose 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 experiments were being made by the Medical Association of the Eure-et-Loir, Dr. Rayer, giving an account in the 'Bulletin de la Société de Biologie de Paris' of the researches he had made, with his colleague, Dr. Davaine, on the contagion of splenic fever, wrote:—'In the blood are found little thread-like bodies about twice the length of a blood corpuscle. These little bodies exhibit no spontaneous motion.'
This is the date of the first observation on the presence of little parasitic bodies in splenic fever, but, strange to say, no attention was paid to these minute filaments. Rayer and Davaine also paid no attention to them. This indifference lasted for thirteen years; it would have lasted longer still, if the parasitic origin of communicable diseases had not been brought before the mind by each new publication of Pasteur's. From 1857 to 1860 it will be remembered that he had demonstrated lactic fermentation, like alcoholic fermentation, 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 Rayer in the blood of splenic fever patients; in 1861 he had announced that no ammoniacal urine existed without the presence 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 sufficient precaution from the veins and the arteries, and urine taken direct from the bladder, could be exposed to the contact of pure air without putrefaction, 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 fermentation, which consists of little cylindrical rods, possessing 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 a great analogy with these vibrios, I was led to examine whether filiform corpuscles, analogous to or of the same kind as those which determined the butyric fermentation, would not, if introduced into the blood of an animal, equally act the part of a ferment. Thus would be easily explained the alteration, and the rapid infection of the mass of the blood, in an animal which had received accidentally or experimentally into its veins a certain number of these bacteria—that is to say, of this ferment.'
But two summers passed before M. Davaine was able to procure a sheep affected with the sang-de-rate. It was only in 1863 that he first recognised the constant presence of a parasite, in the blood of sheep and rabbits which had died from successive inoculations 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 communicate splenic fever.
'In the present state of science,' Davaine concluded, 'no one would think of going beyond these corpuscles to seek for the agent of the contagion. This agent is visible, palpable; it is an organised being, endowed with life, which is developed and propagated in the same manner as other living beings. By its presence, and its rapid multiplication in the blood, it without doubt produces in the constitution of this liquid, after the manner of ferments, modifications which speedily destroy the infected animal.' 'For a long time,' he repeated, 'physicians and naturalists have admitted theoretically that contagious diseases, serious epidemic fevers, the plague, &c., are caused by invisible animalculæ, 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-Grâce, MM. Jaillard and Leplat, sought to refute the preceding conclusions. After having inoculated rabbits and dogs with various putrefying liquids filled with vibrios, they could not cause the death of these animals. To bring about this result it was necessary to introduce into the blood of these dogs and rabbits several cubic centimeters of very putrid liquid. Again in this case, which only added another example to the experiments of Gaspard and Magendie upon the action of putrid liquids, they failed to generate any virulence in the blood. Davaine had no difficulty in showing that MM. Jaillard and Leplat's experiments were made under conditions totally different from his; that he, Davaine, had not made use of the vibrios or bacteria of unselected infusions, but of bacteria which had been found in the blood of sheep which had died from sang-de-rate.
Jaillard and Leplat returned to the charge, and this time with entirely new and unexpected experiments. They inoculated some rabbits, as Davaine desired, with the blood of a cow which had died of splenic fever. The rabbits died rapidly, but without showing before or after their death the least trace of bacteria. Other rabbits, inoculated with the blood of the first, perished in the same manner, but it was still impossible to discover any parasite in their blood. MM. Jaillard and Leplat offered Davaine some drops of this blood. Davaine, taking up the experiments of his opponents, confirmed the exactitude of the facts they had announced, but concluded by saying that these two professors had not employed true splenic fever blood, but the blood of a new disease, unknown up to that time, which Davaine proposed to call the cow disease.
'The blood which we used,' replied MM. Jaillard and Leplat, 'was furnished to us by the director of the knacker's establishment of Sours, near Chartres, and this director is undeniably competent as to the knowledge of splenic fever.'
Full of sincerity and conviction, MM. Jaillard and Leplat recommenced their experiments, using this time the blood of a sheep which had died of splenic fever, and which M. Boutet, the most experienced veterinary surgeon of the town of Chartres, had procured for them. Their results were the same as those obtained with the blood of the cow. Notwithstanding the replies of Davaine, which, however, added nothing to the facts already adduced on one side or the other, it was difficult to pronounce decidedly in such a debate. Unprejudiced minds received from these important discussions the impression that Jaillard and Leplat, in producing facts the exactitude of which were admitted by Dr. Davaine himself, had given a blow to the assertions of the latter, and that the subject required, in every case, new experimental studies.
In 1876, a German physician, Dr. Koch, took up the question. He confirmed the opinion of Davaine, but without in the least producing conviction, 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. 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 presented 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 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 cultivate 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 École Normale, M. Joubert, now Professor of Physics at the Collège Rollin. 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.
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 Rayer 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 unputrescible 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 containing the same liquid as the first and prepared with the same precautions as to sterility and purity, shows itself 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 culture 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 associated in the cultivating liquid with some dissolved substance that it had produced during its life and which acted as a poison. Pasteur accordingly transported some cultivating tubes into the cellars of the Observatory, 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.