Part 15

Some months ago a very hot discussion arose between Pasteur and a commission formed principally of professors of the veterinary school in Turin, regarding the facts above mentioned. One experiment, in the success of which Pasteur was extremely interested, had been made at this school. Instead of employing pure splenic fever blood, free from all contagium, the Italian professors, whether from ignorance of the preceding facts or from inadvertence, employed the blood of a diseased sheep, which, from their own showing, had been dead more than twenty-four hours. Pasteur immediately wrote, pointing out that the commission had done wrong in using blood which must have been at the same time splenic and septic. The Turin professors 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 a microscope, had had this sheep's blood under their eyes. Pasteur contented himself with replying that his assertion rested upon a principle, and that he was perfectly able, without having seen the blood of the sheep, to affirm that under the conditions in which it had been collected that blood was septic. A public correspondence ensued, but no understanding could be come to. Pasteur then offered to go himself to Turin, in order to demonstrate upon as many bodies of sheep dead of splenic fever as they would like to give him, that the blood of these dead bodies--at the end of twenty-four hours if in the month of March, and in twelve or fifteen hours if in the month of June, would be found to be both splenic and septic. Pasteur also proposed, by appropriate cultures, to withdraw at pleasure the splenic fever poison or the septic poison, or the two together, at the choice of the Italians. The Italians, however, shrank from Pasteur's proposal to pay them a visit in order to convince them of their error.

The clearness and certainty of Pasteur's assertions are celebrated, but what gives such authority to all that he advances is, as M. Paul Bert once said, that Pasteur's boldness of assertion is only equalled by his diffidence when he has not experiment to back him up. He never fights except on ground with which he has made himself familiar, but then he fights with such resolution, and sometimes with such impetuosity, that one might say to his adversary, whoever 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' Pasteur, 'take care! Pasteur is never mistaken.'

One day, in 1879, a professor attached to a faculty of medicine in one of the provinces announced to the Academy of Sciences that he had found, in the blood of a woman who had died in a hospital after two weeks' illness from severe puerperal fever, a considerable number of motionless filaments, simple or jointed, transparent, straight, or bent, which belonged to the genus Leptothrix. Engaged in studies on puerperal fever, and having never met with a fact of this kind in his researches, Pasteur wrote at once to this professor to ask him for a specimen of the infected blood. The blood arrived at the laboratory, and some days after Pasteur wrote to the doctor, 'Your leptothrix is nothing else than the bacterium of splenic fever.'

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

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

Then, in the most honourable manner, the doctor hastened to state, in a communication to the Academy of Sciences, that he regretted doubly not having known about splenic fever the year before, as he might have been able, on the one hand, to diagnose the formidable 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 continually.

But to return to our septic vibrios. If air destroys them, if their culture is impossible in contact with air, how can septicæmia exist, since air is everywhere present? How can blood exposed to the air become septic from particles of dust on the surface of objects or which the air holds in suspension? Where can the septic germs be formed? The objection 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 septicæmia. It will be found full of septic vibrios in process of generation by fission. Let this liquid be then exposed to the contact of air, with the precaution of giving a certain depth to the liquid--say, a centimeter of depth. In some hours, if examined with the microscope, the following curious spectacle will be witnessed: In the upper layers the oxygen of the air is absorbed, which is manifested by the already changed colour of the liquid. There the filamentous vibrio dies, and disappears under the form of fine amorphous granulations deprived of virulence. At the bottom of this layer of one centimeter in thickness, on the contrary, the vibrios, protected from the approach of oxygen by those of their own kind which have perished above them, continue to multiply by fission until by degrees they pass into the state of spores; so that instead of moving threads of all dimensions, the length of which sometimes even extends beyond the field of the microscope, nothing is now seen but a dust of brilliant isolated specks, upon which the oxygen of the air has no action. It is thus that a dust of septic germs can be formed even in contact with air. And thus it becomes possible to understand how anaerobic organisms may be sown in putrescible liquids by the dust suspended in the atmosphere. Thus also may be explained the permanence of putrid diseases, even of those which are caused by anaerobic microbes, that cannot live in the atmosphere and which escape destruction 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 organism--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 septicæmia.

II.

In these two virulent maladies, then, splenic fever and septicæmia, the researches of Pasteur had clearly established the parasitic theory. A grand and novel opening was made for future studies on the origin of diseases. Yet, judging from the surprising differences which separate septicæmia and splenic fever, we can foresee that should the future, copying the past, in regard to this and still more recent discoveries, have in store, as it no doubt has, the knowledge of new microbes of disease, the specific properties of these microscopic organisms will demand, for each new exploration, 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 spontaneous disease has no more existence than spontaneous generation. Such aphorisms, however, are not allowed to pass without occasional contradictions, all the more vehement from their rarity. At the International Medical Congress held in London, August 1881, Dr. Bastian, who practises in one of the principal hospitals of London, declared that though he was unable to deny the existence of parasitic diseases, yet, in his opinion, the microbes were the effect and not the cause of these diseases.

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

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

But if a disease like splenic fever is carried by a microbe, this microbe is under the influence of the medium in which it finds itself. It does not develop everywhere. Easily inoculable and fatal to the ox, the sheep, the rabbit, and the guinea pig, splenic fever is very rare in the dog and in the pig. These must be inoculated several times before they contract the disease, and even then it is not always possible to produce it. Again, there are some creatures which are never assailable by it. It can never be taken by fowls. In vain they are inoculated with a considerable quantity of splenic blood; it has no effect upon them. 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 infinitesimal 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 temperature of birds being between 41 and 42 degrees, may it not be, said Pasteur, that the fowls are protected from the disease because their blood is too warm--not far removed from the temperature at which the splenic fever organism can no longer be cultivated? Might not the vital resistance encountered in the living fowl suffice to bridge over the small gap between 41-42, and 44-45 degrees? For we must always allow for a certain resistance in all living creatures to disease and death. No doubt, life to a parasite in the body of an animal would not be as easy as in a cultivating liquid contained in a glass vessel. If the inoculating microbe is aerobic, it can only be cultivated in blood by taking away the oxygen from the globules, which retain it with a certain force for their own life. Nothing was more legitimate than to suppose that the globules of the blood of the fowl had such an avidity for oxygen that the filaments of the splenic parasite were deprived of it, and that their multiplication was thus rendered impossible. This idea conducted Pasteur and his assistants to new researches. 'If the blood of a fowl was cooled,' they asked, 'could not the splenic fever parasite live in this blood?'

The experiment was made. A hen was taken, and, after inoculating it with splenic fever blood, it was placed with its feet in water at 25 degrees. The temperature of the blood of the hen went down to 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 placed in an oven at a temperature of 35 degrees. Little by little its strength returned; it shook itself, settled itself again, and in a few hours was fully restored to health. The microbe had disappeared. Hens killed after having been thus saved, no longer showed the slightest trace of splenic organisms.

How great is the light which these facts throw upon the phenomenon of life in its relation to external physical conditions, and what important inferences do they warrant as to the influence of external media and conditions upon the life and development of living contagia! There have been great discussions 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 foregoing 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.

_FOWL CHOLERA._

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

Here, again, the disease is produced by a microscopic organism. A veterinary surgeon of Alsace, M. Moritz by name, was the first who suspected the presence of microbes in this disease; a veterinary surgeon of Turin, M. Peroncito, depicted it in 1878; a professor of the veterinary school of Toulouse, M. Toussaint, recognised it, in his turn, in 1879, and sent to Pasteur the head of a cock which had died of the cholera. But, however skilful they were, these observers had not succeeded in deciding the question of parasitism. None of them had hit upon a suitable cultivating medium for the parasite, nor had they reared it in successive crops. This, however, is the only method of proving that the virulence belongs exclusively to a parasite.

It is absolutely necessary, in the study of maladies caused by microscopic organisms, to procure a liquid where the infectious parasite can grow and multiply without possible mixture of other organisms of different kinds. An infusion of the muscles of the fowl, neutralised by potash, and rendered sterile by a temperature 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 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. When, for example, the bacterium of splenic fever is sown in the liquid, it assumes in a few hours a surprising 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 inoculated with it? It is innocuous because it cannot develop itself in the body of the animal, or because, its development being arrested, it cannot attain the vital organs.

The decoction extracted from the muscles of the fowl is the only medium which really suits the microbe of fowl cholera. It suffices to inoculate the fowl with the hundredth, even the thousandth, part of a drop of this mixture, to produce the disease and cause death. But here is a strange peculiarity. If guinea-pigs are inoculated with this little parasite they are hardly ever killed by it. Guinea-pigs of a certain age generally exhibit only a local lesion at the point of inoculation, which ends in an abscess more or less prominent. After opening spontaneously, the abscess closes again and heals, while the animal preserves its appetite and its appearance of health. These abscesses sometimes last several weeks. They are surrounded by a pyogenic membrane and filled with a creamy pus, in which the microbe swarms side by side with the pus globules. It is the life of the microbe inoculated under the skin which causes the abscess. The abscess, with the membrane which surrounds it, becomes for the little organism a sort of closed vessel, which it is even easy to tap without sacrificing the guinea-pig. The organism is mixed with the pus in a state of great purity, and although it is localised its virulence is extreme. 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 death of the animal upon which it lives and multiplies, but which can carry death to other species inoculated with it. Fowls and rabbits living among the guinea-pigs suffering from these abscesses might in a moment be smitten and perish, while the health of the guinea-pigs remained unchanged. To produce this result it would suffice that a little of the discharge from the abscess of a guinea-pig should get smeared over the food of the fowls and rabbits. An observer witnessing such deaths without apparent cause, and ignorant of this strange dependency, would no doubt be tempted to believe in the spontaneity of the disease. He would be far from supposing that the evil had originated in the guinea-pigs, which were all in good health. In the history of contagia what mysteries may some day be cleared up by even more simple solutions than this one!

When some drops of the liquid containing this microbe are placed on the food of fowls, the disease penetrates by the intestinal canal. There the little organism increases in such great abundance that inoculation with the excrements of the injected fowls produces 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 thoroughly, especially with water acidulated with a little sulphuric acid, or carbolised water with two grammes of acid to the litre. These liquids readily destroy the microbe, or at least suspend its development. Thus all causes of contagion disappear, because, during their isolation, the animals already smitten die. The action of the disease, in fact, is very rapid.

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

Like the bacillus of splenic fever, the microbe of the fowl cholera is an aerobic organism. It is cultivated 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 respects 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 amorphous granulations, and the blood loses all its virulence. 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 cultivated 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.