A Source Book in Animal Biology

Author: Louis Pasteur  | Date: 1885

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Immunity Via Artificially Attenuated Virus

Louis PASTEUR. Méthode pour prévenir la rage après morsure, in Comptes rendus de l’Académie des Sciences, vol. 101, p. 765, Paris, 1885; tr. by T. S. Hall for this volume.

Prophylaxy in rabies, as I announced it in my name and in the name of my collaborators, in some previous notes, surely constituted real progress in the study of this disease; scientific progress, however, rather than practical. Its application lay open to accidents. Of twenty dogs treated, I could not surely claim to have rendered more than 15 or 16 refractory to rabies.

It was, furthermore, expedient to end the treatment with a final very virulent inoculation, the inoculation of a control virus, so as to fortify and reinforce the refractory state. Besides, prudence required that one keep the dogs under observation during a period longer than the period of incubation of the disease produced by the direct inoculation of this last virus. From which it follows that no less than three or four months must pass before we can feel sure that the state is one of refractoriness toward rabies.

Such requirements would have limited greatly the application of the method.

Finally, only with difficulty could one apply the method to an immediate commencement of treatment, a condition made necessary by the element of the accidental and unforeseen in rabid dog bites.

What was needed, were it possible, was to effect a method more rapid and capable of conferring upon dogs what I would presume to term perfect security.

For how other than by advancing thus far dare one make any trial at all upon man?

After what might be called innumerable trials I achieved a prophylactic method, both prompt and practical, the success of which in dogs has been so frequent and so sure that I have confidence in the applicability of it generally to all animals and to man himself.

This method rests essentially on the following facts:

The inoculation into a rabbit by trepanation, under the dura mater, of a rabic spinal cord of a dog with street rabies, always gives to these animals a case of rabies after an average incubation period of around a fortnight.

If one passes the virus from this first rabbit to a second, from the second to a third, and so on, according to the foregoing procedure there soon is manifested a tendency, increasing in distinctness, toward a diminution of the incubation period of rabies in the rabbits successively inoculated.

After twenty to twenty-five passages from rabbit to rabbit one encounters incubation periods of eight days which remain during a new series of twenty to twenty-five passages. Then one attains an incubation period of seven days which recurs with striking regularity during a new series of up to ninety passages. At any rate it is at this figure that I am at the moment. And it is scarcely if at all that there at present appears a tendency toward an incubation period of a little less than seven days.

Experiments of this type, begun in November 1882, are already three years old, without the series ever having been interrupted and without our ever having recourse to a virus other than those of these rabbits successively dead of rabies. Nothing is easier, thus, than to have constantly at hand arabic virus of perfect purity, always identical or practically so. Upon this hinges the practicability of the method.

Spinal cords of these rabbits are rabic throughout their entire length with constancy of virulence.

If one detaches portions of these cords several centimeters long, utilizing the greatest precautions for purity which it is possible to realize, and if one suspends these in dry air, gradually their virulence diminishes until it finally disappears entirely. The time for extinction of virulence varies very little with the thickness of the pieces, but markedly with the external temperature. The results constitute the scientific point in our method.

These facts established, here is a method for rendering a dog refractory to rabies in a relatively short time.

In a series of flasks in which the air is kept dry by pieces of potash placed on the bottom of the vessel, one suspends each day, a section of fresh rabic cord from a rabbit dead of rabies, developed after seven days’ incubation. Likewise daily, one inoculates under the skin of a dog one full Pravaz syringe of sterilized bouillon in which one has dispersed a small fragment of one of these desiccated cords, commencing with a cord whose order number places it sufficiently far from the day of operation so that we are sure that it is not at all virulent. Previous experiments have established what may be considered safety in this matter. On the following days one proceeds in the same way with more recent cords, separated by an interval of two days, until one arrives at a last very virulent cord which has only been in the flask for a day or two.

At this time the dog is refractory to rabies. One is able to inoculate him with rabic virus under the skin or even on the surface of the brain without rabies declaring itself.

By applying this method, I finally had fifty dogs of every age and breed all refractory without encountering a single failure when unexpectedly there presented themselves at my laboratory upon the sixth of last July three persons from Alsace:

Theodore Vone, a petty merchant grocer of Meissengott near Schlestadt, bitten in the arm July 4th by his own dog which had gone mad;

Joseph Meister, aged nine years, likewise bitten on the 4th of July at 8 o’clock in the morning by the same dog. This child, thrown to the earth by the dog, had numerous bites on his hand, legs, and buttocks, some of them very deep and making walking difficult. The chief wounds had been cauterized with carbolic acid only twelve hours after the accident, at 8 in the evening of July 4th, by Dr. Weber of Ville;

The third person who had herself received no bites was the mother of little Joseph Meister.

At the autopsy of the dog, struck down by its master, the stomach of the dog was found full of straw, hay, bits of wood. The dog had been quite mad. Joseph Meister had been dragged from under the dog covered with saliva and blood.

M. Vone had on his arm some marked contusions, but he assured me that his shirt had not been pierced by the fangs of the dog. Since he had nothing to fear I told him he could leave for Alsace the same day, and he did so. But I kept with me little Joseph Meister and his mother.

Now it happened that it was also on exactly July 6th that the Academy of Science was holding its weekly meeting; I saw there our colleague M. le Dr. Vulpian and told him what had happened. M. Vulpian, as well as Dr. Grancher, were good enough to accompany me at once to Joseph Meister and to confirm the condition and number of his wounds. He had no less than fourteen of them.

The opinions of our colleague and of Dr. Grancher were to the effect that, from the intensity and number of his bites, Joseph Meister had been practically fatally exposed to the inception of rabies. I then communicated to M. Vulpian and M. Grancher the new results I had obtained in the study of rabies since my lecture in Copenhagen a year before.

The death of this child appearing to be inevitable, I decided, not without deep and acute anxiety, as you will well imagine, to try with Joseph Meister the method which had so often proved successful with dogs.

My fifty dogs, it is true, had not been bitten before I commenced to make them refractory, but I knew that this circumstance need not preoccupy me for I had previously already obtained the refractory state in dogs after their being bitten in a large number of cases. I had already presented evidence this year to the rabies Commission of this new and important forward step.

Therefore, on July 6th, at 8 in the evening, sixty hours after the bites of July 4th, and in the presence of Drs. Vulpian and Grancher, Joseph Meister was inoculated under the skin of the hypochondrium, right side, with one half of a Pravaz syringe of cord of a rabbit dead of rabies June 21st and since then preserved in a flask of dry air, namely, for fifteen days.

The days following, new inoculations were made, always in the hypochondrial region according to the conditions which I give in the following table:

In this way I carried to 13 the number of inoculations and to 10 the number of days of treatment. I will explain later that a fewer number of inoculations would have sufficed. But you will understand that in this first attempt I felt obliged to act with the most particular circumspectness.

Each of the cords employed was also inoculated by trepanation into two new rabbits so as to follow the virulence of the materials we were injecting into the human subject.

Study of these rabbits made it possible to verify that the cords of July 6th, 7th, 8th, 9th, and 10th were not virulent, for they did not produce rabies in the rabbits. The cords of July 11th to 16th were all virulent, and the proportion of virulent substance present grew daily greater. Rabies declared itself after seven days’ incubation for rabbits of July 15th and 16th; after eight days for those of the 12th and 14th; after fifteen days for those of July 11th.

During the last days, I had inoculated into Joseph Meister the very most virulent strain of rabies virus, a strain which taken from dogs and reinforced by many passages from rabbit to rabbit gives rabies to rabbits in seven days, to dogs in eight to ten. I felt justified in undertaking to do so because of what happened to the fifty dogs to which I previously referred.

When the immune state has been attained one can without fear inoculate the strongest virus in any quantity whatever. It has always seemed to me that this would have no other effect than to consolidate the refractory state.

Thus, Joseph Meister escaped not only the rabies to which his bites might have given rise but also the virus which I injected as a control upon the immunity got by treatment, and the rabies which I injected was stronger than the street strain.

The final inoculation of this very virulent material has likewise the advantage of cutting down the time during which one need be apprehensive about the aftereffects of a bite. For if the rabies is going to be able to appear, then it will appear much sooner from the injected virus than from the weaker virus of the bite. After the middle of August, I looked forward with confidence toward the future soundness of Joseph Meister. Today as well, after a lapse of three months and three weeks since the accident, his health leaves nothing to be desired.

What interpretation is to be made of this new method which I have just made known for preventing rabies after the bite? I do not intend today to treat this question in a complete fashion. I wish to limit myself to some preliminary details having to do with the understanding of the meaning of the experiments which I am now pursuing in an effort to focus upon the best of the interpretations possible.

Returning now to the method for progressive attenuation of a fatal virus and the prophylaxy which one can derive therefrom, the influence of air upon this attenuation being given, the first idea which presents itself in explanation of the effect of the method is that the sojourn of the cords in contact with dry air progressively diminishes the intensity of their virulence to the disappearing point.

From this, one would be persuaded that the prophylactic procedure in question rests upon the use first of a virus without appreciable virulence, next weak ones, and then stronger and stronger ones.

I will show finally that the facts do not agree with this way of looking at the matter. I will prove that the delays in the incubation period of the rabies given to rabbits day by day, such as I was speaking about above, given to check the state of the virulence of the cords desiccated in contact with air, are an effect of the impoverishment of the quantity of the virus present in these cords and not an effect of the impoverishment of the virulence.

Could one admit that the introduction of a virus of constant virulence would produce immunity—if one used very small quantities increasing them daily? This is an interpretation of my method which I have studied from the experimental point of view.

One can give the new method another interpretation, an interpretation certainly very foreign to the foregoing, but one which merits full consideration because it is in harmony with certain already achieved results in connection with vital phenomena in certain lower organisms, notably different pathogenic microbes.

Many microbes appear to give rise in their culture media to substances injurious to their own development.

In 1880, I began researches to establish that the microbe of chicken cholera produces a sort of self-poisoning substance. I did not succeed in demonstrating such a substance; but I feel today that the study should be taken up again—nor shall I fail to do so—operating in the presence of pure carbonic acid gas. ...

M. Raulin, my old teacher, now professor of the Faculty of Lyon, has established, in a very remarkable thesis which he defended at Paris, March 22, 1870, that the growth of aspergillus niger develops a substance which partially arrests the growth of this mold when the culture medium does not contain iron salts.

Could it not be that the rabies virus is composed of two distinct substances so that in addition to that which is living and able to reproduce in the nervous system, there is another having the faculty when present in suitable amounts of stopping the development of the foregoing? I will examine this third interpretation of the method of prophylaxy in rabies with all the attention it deserves in my next communication.

I scarcely need to mention in closing that perhaps the most important question to be resolved at this time is that of what interval to observe between the instant of the bite and the commencement of the treatment. That interval in the case of Joseph Meister was two and a half days. But we must be prepared for situations in which it is much longer.

Last Tuesday, October 20th, with the obliging assistance of MM. Vulpian and Grancher, I had to start treating a youth of 15 years, bitten six days before on both hands and in very serious condition.

I shall not delay in informing the Academy of the outcome from this new attempt.

Probably it will not be without emotion that the Academy will hear the account of the courageous act and presence of mind of this boy whom I started treating Tuesday last. He is a shepherd, fifteen years old, named Jean-Baptiste Jupille, from Villers-Farlay (Jura) who, on seeing a dog of suspicious actions and great size leap upon a group of six small friends of his, all younger than he was, lept forward, armed with his whip, in front of the animal. The dog seized Jupille’s left hand in its mouth. At this, Jupille knocked the dog over, held it down, opened its mouth with his right hand, meanwhile receiving several new bites, and then, with the thong of his whip hound the dog’s muzzle and dispatched the animal with one of his wooden shoes. [Abstracts from comments succeeding the reading of Pasteur’s paper]

VULPIAN: The Academy will not be astonished if, as a member of the Section on Medicine and Surgery, I seek the chair’s recognition to express the feelings of admiration which M. Pasteur’s communication inspires in me. The sentiments will be shared, I am sure, by the entire medical profession. Etc.

LARREY: ... I therefore take the honor of moving that the Academy recommend to the French Academy that this young shepherd has, in giving so generous an example of courage, rendered himself deserving of a "prize of virtue."

BOULEY (President of the Academy): The Communication which we have just heard permits the Academy, and I might even say humanity, to conceive new hopes.

Likewise the date of October 27, 1885, will remain as one of the most memorable, if it is not the most memorable, in the history of scientific conquests and in the Annals of the Academy.


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Chicago: Louis Pasteur, "Immunity Via Artificially Attenuated Virus," A Source Book in Animal Biology, trans. T. S. Hall in A Source Book in Animal Biology, ed. Thomas S. Hall (New York: Hafner Publishing Company, 1951), 528–534. Original Sources, accessed April 18, 2021, http://www.originalsources.com/Document.aspx?DocID=JAP9DH43XXM1IWZ.

MLA: Pasteur, Louis. "Immunity Via Artificially Attenuated Virus." A Source Book in Animal Biology, translted by T. S. Hall, Vol. 101, in A Source Book in Animal Biology, edited by Thomas S. Hall, New York, Hafner Publishing Company, 1951, pp. 528–534. Original Sources. 18 Apr. 2021. www.originalsources.com/Document.aspx?DocID=JAP9DH43XXM1IWZ.

Harvard: Pasteur, L, 'Immunity Via Artificially Attenuated Virus' in A Source Book in Animal Biology, trans. . cited in 1951, A Source Book in Animal Biology, ed. , Hafner Publishing Company, New York, pp.528–534. Original Sources, retrieved 18 April 2021, from http://www.originalsources.com/Document.aspx?DocID=JAP9DH43XXM1IWZ.