Part 21

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. Rossignol, 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 inoculated, 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.

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

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

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

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

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

An extraordinary movement was everywhere produced in favour of vaccination. A great number of agricultural societies wished to repeat the celebrated experiment of Pouilly-le-Fort. The breeders of cattle overwhelmed Pasteur with applications for vaccine. Pasteur was obliged to start a small manufactory for the preparation of these vaccines in the Rue 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 application of this new system, the results were topical. Among flocks where half had been vaccinated and the other half not vaccinated--all the animals continuing 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 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 attributing to vaccination the losses which in reality belong to the natural disease. Just as human vaccination 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 immunity to animals after splenic vaccination cannot be compared with the duration of immunity from small-pox after Jennerian vaccination. Jenner and his contemporaries believed that vaccination was able to preserve from small-pox during the whole life. That illusion disappeared long ago, and now ten years has been fixed as the average duration of that immunity and of the interval which ought to separate successive vaccinations. This interval, moreover, is too long for a certain number of individuals. Besides, in order to judge of the immunity of antisplenic vaccination, we must not lose sight of the formidable trial which vaccinated animals have to undergo when inoculated with the most virulent virus. What doctor would dare to subject a vaccinated child to inoculation from 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 expression may be used--the average scarcely exceeds three years. The duration, then, of the immunity that vaccination confers is about a third of the duration of the animal's life.

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 in the bodies of animals inoculated with them, and fixed them in media appropriate to their life, Pasteur asked himself whether it would not be possible to restore to these attenuated microbes--weakened to such a degree as to have lost all virulence--a deadly virulence, and to render them again capable of living and multiplying in the bodies of animals.

Experiment soon confirmed this mental prevision. 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 oxygenation of the blood globules is not as yet capable of preventing the aerobic microbe from turning to its own account the oxygen of the blood. The disease does its work and death supervenes.

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

The same is the case with the microbe of fowl cholera. When it has ceased to have any effect upon fowls, its virulence can be restored by inoculating small birds. Blackbirds, canaries, sparrows, all die, if the virus has not been too much attenuated; and the effect is similar on young chicks. Thus by several successive transitions from bird to bird a virulence may be fostered capable of destroying full-grown fowls.

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

'The accounts which I have read,' Pasteur remarked some months ago, 'of the spontaneous appearance 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 malignant disease belonging to certain countries, has germs of long duration. In all these countries its attenuated virus must exist, ready to resume its active form whenever the conditions of climate, of famine, of misery present themselves afresh. The condition of long duration in the vitality of the germs of evil is not even indispensable; for, if I may believe the doctors who have visited these countries, in all places subject to the plague, and in the intervals of the 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 probable that these boils contain an attenuated virus of the plague, and that the passage of this virus into exhausted 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 reinforced.'

ETIOLOGY OF SPLENIC FEVER.

M. Pasteur had triumphed over splenic fever with as much rigour as precision. But he considered that he had still to make one further investigation. He had established the effects of the pest; he had discovered a preventive method with which to combat it: he now wished to know the origin of the evil. Whence comes splenic fever? Why is it endemic in certain departments of France, in certain parts of Russia, Germany, Austria, Italy, Spain, and America? How is it sustained? 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 Agriculture, 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, 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 richness 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 demonstrated to what extent it was fitted to furnish crops that were rich and abounding in nutritive properties. He analysed the plants. He then complacently referred 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 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 Delafond was led,' adds M. Bouley, ridiculing these observations, 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 Montargis 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 inspiration that gave them birth, we can see the progress that has since been made, and can realise how great were the obscurity and uncertainty which have been dispelled by the experimental method.

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