Pasteur’s Communications on Rabies: No. 5

May 19, 1884. — The Attenuation of Rabies. — The great notions of the variability in the virulence of certain viruses, and of the preservation against a given virus by the inoculation of another of lower intensity, are to-day recognised scientific facts already put to practical uses. It is easy to apprehend all the interest attaching, in that line of stud to the search after methods of attenuation applicabl to new viruses.

I bring news to-day of one more step forward in that direction as concerns rabies.

  1. The virus of rabies carried from the dog to the monkey, and subsequently from monkey to monkey, grows weaker at each passage. After the virulence has thus diminished by several passages through monkeys, if the virus be carried back to the dog or to the rabbit or to the guinea-pig, it still remains attenuated. In other words, the virulence does not at one bound go back to the degree it had in the clog ‘ a rage des rues ‘ — affected with ordinary or street madness.
    In those conditions a small number of passages from monkey to monkey suffice to bring down the attenuation to a point at which the virus injected hypodermically into dogs never gives rise to rabies in them. Intra-cranial inoculation itself, the neverfailing means of communicating rabies, may now remain without effect, whilst, however, creating a refractory state in favour of the inoculated animal.
  2. Successive passages from rabbit to rabbit and from guinea-pig to guinea-pig increase the virulence of rabies virus. This exalted virulence comes to a fixed maximum in the rabbit. If now transferred to the dog it remains exalted, and shows itself to be much more intensely virulent than the virus of ordinary street rabies. So great is this acquired virulence, that the new virus injected into the blood-system of a dog unfailingly gives rise to mortal madness.
  3. The virulence of rabies virus, as we have seen, is exalted by its passages through rabbits or through guinea-pigs, but it requires many such passages before it again reaches its maximum degree after it has been weakened in the monkey. In the same way the virus of ordinary canine madness, as I have just said, is far from possessing the maximum degree of virulence, and it requires several passages through rabbits before it reaches that maximum.

A logical application of the results just indicated gives us the means of easily rendering dogs refractory to rabies, for we can now prepare and keep at our disposal a set of attenuated viruses of different strength, some, not mortal, preserving the animal economy against the ill effects of more active ones, and these latter against the effects of mortal ones.

Let us give an example : take a rabbit which has been inoculated on the brain, and which has died of rabies after a period of incubation longer by several days than the shortest known incubation in the rabbit (this is always comprised between seven and eight days after intra-cranial inoculation of the maximum virus). Extract the virus from this longincubation rabbit and inject it, after trephining, into a second rabbit. Similarly inoculate a third rabbit from this second one. These viruses have grown stronger each time ; each time also that they are inoculated into a fresh rabbit, let us inoculate them into the same dog. This dog, after the third inoculation, has become capable of bearing unhurt inoculations of a mortal virus. He has become entirely refractory to the rabies of ordinary canine madness, whether inoculated into a vein or into the arachnoid space.

By inoculating the blood of rabid animals, under certain well-determined circumstances, I have been able considerably to simplify the process of vaccination, whilst at the same time putting the dog in a most decidedly refractory state. I shall on an early occasion acquaint the Academy with the sum of my experiments on that point.

In the meantime, and until we come to that remote epoch when vaccination shall have stamped out rabies from our midst, it would be highly advantageous to have the means of preventing the development of that affection after the bite of mad dogs. The first attempts I have made in that direction inspire me with the greatest hopes of success. Owing to the long incubative period of rabies I have every reason to believe that we shall be able with certainty, after the bite, to put the patients in a refractory state before the first symptoms of the mortal malady show themselves.

The first experiments testify strongly in favour of this view, but afferent proof must be collected from different animal races, and almost ad infinitum, before human therapeutics can make bold enough to try this mode of prophylaxis on man himself.

Notwithstanding the confidence I derive from the large number of the experiments I have made in the last four years, it is not without some excusable apprehension that I publish to-day a set of facts which point to no less a result than the possible prophylaxis of rabies. Had I been able to dispose of the necessary materials I should have been glad before giving this communication to wait until I had begged of some of my colleagues of the Academy of Sciences and of the Academy of Medicine kindly to witness and to control the conclusions I have just brought forward.

In order to obey those scruples and those reasons I took the liberty of writing a few days ago to M. Fallieres, Minister of Public Instruction, requesting of him to appoint a commission before which I might bring my rabies-refractory dogs.

The crucial experiment to be tried in the first instance would be the following. I should take from my kennels twenty refractory dogs, which I should place, for the sake of comparison, by the side of twenty ordinary, non-vaccinated control dogs. We should then have the forty dogs brought in with mad dogs and bitten by them. If the facts announced by me are real, not one of my twenty dogs will take rabies, Vhereas the twenty control animals will take it.

A second experiment, no less conclusive than the first, would consist in taking forty dogs, whereof twenty should be vaccinated before the eyes of the commission and twenty should remain not vaccinated. The forty animals will then be trepanned and inoculated on the brain with the virus of ordinary street-dog rabies. The twenty vaccinated dogs will not take rabies but the twenty others will all die of it, taking it either in its paralytic or in its furious form.

The following communication was made to the members of the International Medical Congress sitting in Copenhagen, on August 11, 1884. Although not a communication to the Academic des Sciences, we give it here in full, because of its intrinsic interest and importance, and also because it forms an otherwise missing link between some of the other articles :

‘Gentlemen, — Your Congress meetings are the place for the discussion of the gravest problems of medicine ; they serve also to point out the great landmarks of the future. Three years ago, on the eve of the London Congress, the doctrine of microorganisms, the setiological cause of transmissible maladies, was still the subject of sharp criticisms. Certain refractory minds continued to uphold the idea that ” disease is in us, from us, by us.”‘ It was expected that the decided supporters of the theory of the spontaneity of diseases would make a bold stand in London ; but no opposition was made to the doctrine of ” exteriority,” or external causes, the first cause of contagious diseases, and those questions were not discussed at all.

‘ It was there seen, once again, that when all is ready for the final triumph of truth, the united conscience of a great assembly feels it instinctively and recognises it.

‘ All clear-sighted minds had already foreseen that the theory of the spontaneity of diseases received its death-blow on the day when it became possible reasonably to consider the spontaneous generation of microscopic organisms as a myth, and when, on the other hand, the life-activity of those same beings was shown to be the main cause of organic decomposition and of all fermentation.

‘ From the London Congress, also, dates the recognition of another very hopeful progress, we refer to the attenuation of different viruses, to the production of varying degrees of virulence for each virus, and their preservation by suitable methods of cultivation ; to the practical application, finally, of those new facts in animal medicine.

‘ New microbic prophylactic viruses have been added to those of fowl-cholera and of splenic fever. The animals saved from death by contagious diseases are now counted bv hundreds of thousands, and the sharp opposition which those scientific novelties met with at the beginning was soon swept away by the rapidity of their onward progress.

‘ Will the circle of practical applications of those new notions be limited in future to the prophylaxis of animal distempers ‘? We must never think little of a new discovery, nor despair of its fecundity ; but more than that, in the present instance, it may be asserted that the question is already solved in principle. Thus, splenic fever is common to animals and man, and we make bold to declare that, were it necessary to do so, nothing could be easier than to render man also proof against that affection. The process which is employed for animals might, almost without a change, be applied to him also. It would simply become advisable to act with an amount of prudence which the value of the life of an ox or a sheep does not call for. Thus, we should use three or four vaccineviruses instead of two, of progressive intensity of virulence, and choose the first ones so weak that the patient should never be exposed to the slightest morbid complication, however susceptible to the disease he might be by his constitution.

‘ The difficulty, then, in the case of human diseases, does not lie in the application of the new method of prophylaxis, but rather in the knowledge of the j)h} T siological properties of their viruses. All our experiments must tend to discover the proper degree of attenuation for each virus. But experimentation, if allowable on animals, is criminal on man. Such is the principal cause of the complication of researches bearing on diseases exclusively human. Let us keep in mind, nevertheless, that the studies of which we are speaking were born yesterday only, that they have already yielded valuable results, and that new ones may be fairly expected when we shall have gone deeper into the knowledge of animal maladies, and of those in particular which affect animals in common with man.

‘ The desire to penetrate farther forward in that double study led me to choose rabies as the subject of my researches, in spite of the darkness in which it was veiled.

‘ The study of rabies was begun in my laboratory four years ago, and pursued since then without other interruption than what was inherent to the nature of the researches themselves, which present certain unfavourable conditions. The incubation of the disease is always protracted, the space disposed of is never sufficient, and it thus becomes impossible at a given moment to multiply the experiments as one would like. Notwithstanding those material obstacles, lessened by the interest taken by the French Government in all questions of great scientific interest, we now no longer count the experiments which we have made, my fellowworkers and myself. I shall limit myself to-day to an exposition of our latest acquisitions.

‘ The name alone of a disease, and of rabies above all others, at once suggests to the mind the notion of a remedy.

‘ But it will, in the majority of cases, be labour lost to aim in the first instance at discovering a mode of cure. It is, in a manner, leaving all progress to chance. Far better to endeavour to acquaint oneself, first of all, with the nature, the cause, and the evolution of the disease, with a glimmering hope, perhaps, of finally arriving at its prophylaxis.

‘ To this last method we are indebted for the result that rabies is no longer to-day to be considered as an insoluble riddle.

‘ We have found that the virus of rabies develops itself invariably in the nervous system, brain, and spinal cord, in the nerves, and in the salivary glands ; but it is not present at the same moment in every one of those parts. It may, for example, develop itself at the lower extremity of the spinal cord, and only after a time reach the brain. It may be met with at one or at several points of the encephalon whilst being absent at certain other points of the same region.

‘ If an animal is killed whilst in the power of rabies, it may require a pretty long search to discover the presence here or there in the nervous system, or in the glands, of the virus of rabies. We have been fortunate enough to ascertain that in all cases, when death has been allowed to supervene naturally, the swelled-out portion, or bulb, of the medulla oblongata nearest to the brain, and uniting the spinal cord with it, is always rabid. When an animal has died of rabies (and the disease always ends in death), rabid matter can with certainty be obtained from its bulb, capable of reproducing the disease in other animals when inoculated into them, after trephining, in the arachnoid space of the cerebral meninges.

‘ Any street dog whatsoever, inoculated in the manner described with portions of the bull) of an animal which has died of rabies, will certainly develop the same disease. We have thus inoculated several hundreds of dogs brought without any choice from the pound. Never once was the inoculation a failure. Similarly also, with uniform success, several hundred guinea-pigs, and rabbits more numerous still.

‘ Those two great results, the constant presence of the virus in the bulb at the time of death, and the certainty of the reproduction of the disease by inoculation into the arachnoid space, stand out like experimental axioms, and their importance is paramount. Thanks to the precision of their application, and to the well-nigh daily repetition of those two criteria of our experiments, we have been able to move forward steadily and surely in that arduous study. But, however solid those experimental bases, they were, nevertheless, incapable in themselves of giving us the faintest notion as to some method of vaccination against rabies. In the present state of science the discovery of a method of vaccination against some virulent malady presupposes :

‘ 1. That we have to deal with a virus capable of assuming diverse intensities, of which the weaker ones can be put to vaccinal or protective uses.

‘ 2. That we are in possession of a method enabling us to reproduce those diverse degrees of virulence at will.

‘ At the present time, however, science is acquainted with one sort of rabies only — viz., dog rabies.

‘ Rabies, whether in dog, man, horse, ox, wolf, fox, &c, comes originally from the bite of a mad. dog. It is never spontaneous, neither in the dog nor in any other animal. There are none seriously authenticated among the alleged cases of so-called spontaneous rabies, and I add that it is idle to argue that the first case of rabies of all must have been spontaneous. Such an argument does not solve the difficulty, and wantonly calls into question the as yet inscrutable problem of the origin of life. It would be quite as well, against the assertion that an oak-tree always proceeded from another oaktree, to argue that the first of all oak-trees that ever grew must have been produced spontaneously. Science, which knows itself, is well aware that it would be useless for her to discuss about the origin of things ; she is aware that, for che present at any rate, that origin is placed beyond the ken of her investigations.

‘ In fine, then, the first question to be solved on our way towards the prophylaxis of rabies is that of knowing whether the virus of that malady is susceptible of taking on varying intensities, after the manner of the virus of fowl-cholera or of splenic fever.

‘ But in what way shall we ascertain the possible existence of varying intensities in the virus of rabies ? By what standard shall we measure the strength of a virus which either fails completely or kills ? Shall we have recourse to the visible symptoms of rabies? But those symptoms are extremely variable, and depend essentially on the particular point of the encephalon or of the spinal cord where the virus has in the first instance fixed and developed itself. The most caressing rabies, for such do exist, may, when inoculated into another animal of the same species, give rise to furious rabies of the intensest type.

‘ Might we then perhaps make use of the duration of incubation as a means of estimating the intensity of our virus ? But what can be more changeful than the incubative period ? Suppose a mad dog to bite several sound dogs : one of them will take rabies in one month or six weeks, another after two or three months or more. Nothing, too, more changeful than the length of incubation according to the different modes of inoculation. Thus, other circumstances the same, after bites or hypodermic inoculation rabies occasionally develops itself, and at other times aborts completely ; but inoculations on the brain are never sterile, and give the disease after a relatively short incubation.

‘ It is possible, nevertheless, to gauge with sufficient accuracy the degree of intensity of our virus by means of the time of incubation, on condition that we make use exclusively of the intra-cranial mode of inoculation ; and secondly, that we do away with one of the great disturbing influences inherent to the results of inoculation made by bites, under the skin, or in the veins, by injecting the right proportion of material.

‘ The duration of incubation, as a matter of fact, may depend largely on the quantity of efficient virus — that is to say, on the quantity of virus which reaches the nervous system without diminution or modification. Although the quantity of virus capable of giving rabies may be, so to speak, infinitely small, as seen in the common fact of the disease developing itself after rabid bites which, as a rule, introduce into the system a barely appreciable weight of virus, it is easy to double the length of incubation by simply changing the proportion of those very small quantities of inoculated matter. I may quote the following examples :

‘ On May 10, 1882, we injected into the popliteal vein of a dog ten drops of a liquid prepared by crushing a portion of the bulb of a dog, which had died of ordinary canine madness, in three or four times its volume of sterilised broth.

‘ Into a second dog we injected 1/100th of that quantity, into a third 1/200th. Rabies showed itself in the first dog on the eighteenth day after the injection, on the thirty-fifth day in the second dog, whilst the third one did not take the disease at all, which means that, for that last animal, with the particular mode of inoculation employed, the quantity of virus injected was not sufficient to give rabies. And yet that dog, like all dogs, was susceptible of taking the disease, for it actually took it twenty-two days after a second inoculation, performed on September 3, 1882.

‘ I now take another example bearing on rabbits, and by a different mode of inoculation. This time, after trephining, the bulb of a rabbit which had died of rabies after inoculation of an extremely powerful virus is triturated and mixed with two or three times its volume of sterilised broth. The mixture is allowed to stand a little, and then two drops of the supernatant liquid are injected after trephining into a first rabbit, into a second rabbit one-fourth of that quantity, and in succession into other rabbits, 1/15th, 1/64th, 1/128th, and 1/152nd of that same quantity. All those rabbits died of rabies, the incubation having been eight days, nine and ten days for the third and fourth, twelve and sixteen days for the last ones.

‘ Those variations in the length of incubation were not the result of any weakening or diminution of the intrinsic virulence cf the virus brought on possibly by its dilution, for the incubation of eight days was at once recovered when the nervous matter of all those rabbits was inoculated into newanimals.

‘ Those examples show that, whenever rabies follows upon bites or hypodermic inoculations, the differences in respect of length of incubation must be chiefly ascribed to the variations, at times within considerable limits, of the ever-undeterminate proportions of the inoculated viruses which reach the central nervous system.

‘ If, therefore, we desire to make use of the length of incubation as a measure of the intensity of the virulence, it will be indispensable to have recourse to inoculation on the surface of the brain, after trephining, a process the action of which is absolutely certain, coupled with the use of a larger quantity of virus than what is strictly sufficient to give rise to rabies. By those means the irregularities in the length of incubation for the same virus tend to disappear completely, because we always have the maximum effect which that virus can produce ; that maximum coincides with a minimum length of incubation.

‘ We have thus, finally, become possessed of a method enabling us to investigate the possible existence of different degrees of virulence, and to compare them with one another. The whole secret of the method, I repeat, consists in inoculating on the brain, after trephining, a quantity of virus which, although small in itself, is still greater than what is simply necessary to reproduce rabies. We thus disengage the incubation from all disturbing influences and render its duration dependent exclusively on the activity of the particular virus used, that activity being in each case estimated by the minimum incubation determined by it.

‘ This method was applied in the first instance to the study of canine madness, and in particular to the question of knowing whether dog-madness was always one and the same, with perhaps the slight variations which might be due to the differences of race in diverse dogs.

‘ We accordingly got hold of a number of dogs affected with ordinary street rabies, at all times of the year, at all seasons of the same year or of different years, and belonging to the most dissimilar canine races. In each case the bulbar portion of the medulla oblongata was taken out from the recently dead animal, triturated and suspended in two or three times its volume of sterilised liquid, making use all along of every precaution to keep our materials pure, and two drops of this liquid injected after trephining into one or two rabbits. The inoculation is made with a Pravaz syringe, the needle of which, slightly curved at its extremity, is inserted through the dura-mater into the arachnoid space. The results were as follows : all the rabbits, from whatever sort of dog inoculated, showed a period of incubation which ranged between twelve and fifteen days, without almost a single exception. Never did they show an incubation of eleven, ten, nine, or eight days, never an incubation of several weeks or of several months.

‘ Dog-rabies, the ordinary rabies, the only known rabies, is thus sensibly one in its virulence, and it modifications, which are very limited, appear to depend solely on the varying aptitude for rabies the different known races. But we are going now to witness a deep change in the virulence of dograbies.

‘ Let us take one, any one, of our numerous rabbits, inoculated with the virus of an ordinary mad dog, and, after it has died, extract its “hull-, prepare it as just described, and inject two drops of the bulb-emulsion into the arachnoid space oi a second rabbit whose bull) will in turn and in time be injected into a third rabbit, the bulb which again will serve for a fourth rabbit, and so on.

‘ There will be evidence, even from the first few passages, of a marked tendency towards a lessening of the period of incubation in the succeeding rabbits. Just one example :

‘ Towards the end of the year 1882, fifteen cows and one bull died of rabies in a farm situated in the neighbourhood of the town of Melun. They had been bitten on October 2 by the farm-dog, which had become mad. The head of one of the cows, which had died on November 15, was sent to my laboratory by M. Kossignol, a veterinary surgeon in Melun. A number of experiments were made on dogs and on rabbits, and showed that the following parts, the only encephalic (or those pertaining to the brain) ones tested, were rabid : the bulb, the cerebellum, the frontal lobe, the sphenoidal lobe. The rabbits trephined and inoculated with those different parts showed the first symptoms of rabies on the seventeenth and the eighteenth days after inoculation. With the bulb of one of those rabbits two more were inoculated, of which one took rabies on the fifteenth day, the other on the twenty-third day.

‘ We may notice, once for all, that when rabies is transferred from one animal to another of a different species, the period of incubation is always very irregular at first in the individuals of the second species if the virus had not yet become fixed in its maximum virulence for the first species. We have just seen an example of that phenomenon, since one of the rabbits had an incubation of fifteen days, the other of twenty-three days, both having received the same virus and all other circumstances remaining apparently the same for them.

‘ The bulb of the first one of those last rabbits which died was injected into two more rabbits, still after trephining. One of them took rabies on the tenth day, the other on the fourteenth day. The bulb of the first one that died was again injected into a couple of new rabbits, which developed the disease in ten days and twelve days respectively. A fifth time two new animals were inoculated from the first one that died, and they both took the disease on the eleventh day after inoculation ; similarly, a sixth passage was made, and gave an incubation of eleven days, twelve days for the seventh passage, ten and eleven for the eighth, ten days for the ninth and tenth passages, nine days for the eleventh, eight and nine days for the twelfth, and so on, with differences of twenty-four hours at the most, until we got to the twenty-first passage, when rabies declared itself in eight days, and subsequently to that always in eight days up to the fiftieth passage, which was only effected a few days ago. That long experimental series which is still going on was begun on November 15, 1882, and will be kept up for the purpose of preserving in our rabies virus that maximum virulence which it has come to now for some considerable time, as it is easy to calculate.

‘ Allow me to call your attention to the ease and safety of the operations for trephining and then inoculating the virus. Throughout the last twenty months we have been able without a single interruption in the course of the series to carry the one initial virus through a succession of rabbits which were all trephined and inoculated every twelfth day or so.

‘ Guinea-pigs reach more rapidly the maximum virulence of which they are susceptible. The period of incubation is in them also variable and irregular at the beginning of the series of successive passages, but it soon enough fixes itself at a minimum of five days. The maximum virulence in guinea-pigs is reached after seven or eight passages only. It is worth noting that the number of passages required before reaching the maximum virulence, both in guinea-pigs and in rabbits, varies with the origin of the first virus with which the series is begun.

‘ If now this rallies with maximum virulence be transferred again into the dog from guinea-pig or rabbit, there is produced a dogvirus which in point of virulence goes far beyond that of ordinary canine madness.

‘ But, a natural query — of what use can be thai discovery as to the existence and artificial production of diverse varieties of rabies, every one of them more violent and more rapidly fatal than the habitual madness of the dog ? The man of science is thankful for the smallest find he can make in the field of pure science, but the many, terrified at the very name of hydrophobia, claim something more than mere scientific curiosities. Plow much more interesting it would be to become acquainted with a set of rabies viruses which should, on the contrary, be possessed of attenuated degrees of virulence! Then, indeed, might there be some hope of creating a number of vaccinal rabies viruses such as we have done for the virus of fowl-cholera, of the microbe of saliva, of the red evil of .-wine (swine-plague), and even of acute septicaemia. Unfortunately, however , the methods which had served for those different viruses showed themselves to be either inapplicable or inefficient in the case of rabies. It, therefore, became necessary to find out new and independent methods, such, for example, as the cultivation in vitro of the mortal rabies virus. ‘

Jenner was the first to introduce into current science the opinion that the virus which he called the grease of the horse, and which we call now more exactly horse-pox, probably softened its virulence, so to speak, in passing through the cow and before it could be transferred to man without danger. It was, therefore, natural to think of a possible diminution of the virulence of rabies by a number of passages through the organisms of some animal or other, and the experiment was worth trying. A large number of attempts were made, but the majority of the animal species experimented on exalted the virulence after the manner of rabbits and guinea-pigs ; fortunately, however, it was not so with the monkey.

‘ On December 6, 1888, a monkey was trephined and inoculated with the bulb of a dog, which had itself been similarly inoculated from a child who had died of rabies. The monkey took rabies eleven days later, and when dead served for inoculation into a second monkey which also took the disease on the eleventh day. A third monkey, similarly inoculated from the second one, showed the first symptoms on the twenty-third day, &c. The bulb of each, one of the monkeys was inoculated, after trephining, into two rabbits each time. The rabbits inoculated from the first monkey developed rabies between thirteen and sixteen days, those from the second monkey between fourteen and twenty days, those from the third monkey between twenty-six and thirty days, those from the fourth monkey both of them after the twenty-eighth day, those from the fifth monkey after twenty-seven days, those from the sixth monkey after thirty days.

‘ It cannot be doubted after that, that successive passages through monkeys, and from the several monkeys to rabbits, do diminish the virulence of the virus for the latter animals ; they diminish it for dogs also. The dog inoculated with the bulb of the fifth monkey gave an incubation of no less than fifty-eight days, although it had been inoculated in the arachnoid space.

‘ The experiments were renewed with fresh sets of monkeys and led to similar results. We were, therefore, actually in possession of a method by means of which we could attenuate the virulence of rabies. Successive inoculations from monkey to monkey elaborate viruses which, when transferred to rabbits, reproduce rabies in them, but with a progressively lengthening period of incubation. Nevertheless, if one of those rabbits be taken as the first for inoculations through a series of rabbits, the rabies thus cultivated obeys the law which we have seen before, and has its virulence increased at each passage.

‘ The practical application of those facts gives us a method for the vaccination of dogs against rabies. As a starting-point, make use of one of the rabbits inoculated from a monkey sufficiently re‘ moved from the first animal of the monkey series for the inoculation — hypodermic or intravenous — of that rabbit’s bulb not to be mortal for a new rabbit. The next vaccinal inoculations are made with the bulbs of rabbits derived by successive passages from that first rabbit.

‘ In the course of our experiments we made use, as a rule, for inoculation, of the virus of rabbits which had died after an incubation of four weeks, repeating three or four times each the vaccinal inoculations made with the bulbs of rabbits derived in succession from one another and from the first one of the series, itself coming directly from the monkey. I abstain from giving more details, because certain experiments which are actually going on allow me to expect that the process will be greatly simplified.

‘You must be feeling, gentlemen, that there is a great blank in my communication ; I do not speak of the micro-organism of rabies. We have not got it. The process for isolating it is still imperfect, and the difficulties of its cultivation outside the bodies of animals have not yet been got rid of, even by the use, as pabulum, of fresh nervous matter. The methods which we employed in our study of rabies ought all the more perhaps, on that account, to fix attention. Long still will the art of preventing diseases have to grapple with virulent maladies the micro-organic germs of which will escape our investigations. It is, therefore, a capital scientific fact that we should be able, after all, to discover the vaccination process for a virulent disea 1 without yet having at our disposal its special virus and whilst yet ignorant of how to isolate or to cultivate its microbe.

‘ As soon as the method for the vaccination of dogs was firmly established, and we had in our posjsion a large number of dogs which had been rendered refractory to rabies, I had the idea of submitting to a competent committee those of the facts which appeared destined in future to serve as a basis for the vaccination of dogs against rabies. That course was suggested to me, in prevision of the later practical application of the method, by the recollection of the opposition with which Jenner’s discovery met at its beginning.

‘ I spoke of my project to M. Fallieres, the Minister of Public Instruction, who was pleased to approve of it and gave commission to the following gentlemen to control the facts which I had summarily communicated to the Academy of Sciences in its sitting of May 19 last : Messrs. Beclard, Paul Bert, Bouley, Aimeraud, Villemm, Vulpian. M. Bouley was appointed president, Dr. Villemin secretary, and the commission at once set to work. I have the pleasure of informing you that it has just sent in a first report to the Minister. I was acquainted with it here, and the following are in a few words the facts related in that first report on rabies. I had given to the commission nineteen vaccinated dogs in succession — that is to say, dogs which had been rendered refractory by preventive inoculations. Thirteen only of them had after their vaccination been already submitted to the test-inoculation on the brain.

‘ The nineteen dogs were, for the sake of comparison, divided into sets along with nineteen more control dogs brought from the pound without any sort of selection. To begin with, two refractory dogs and two control dogs were on June 1 trephined and inoculated under the dura-mater, on the surface of the brain, with the bulb of a dog affected with ordinary street rabies.

‘ On June 3 another refractory dog and another control dog were bitten by a furious street mad dog.

‘ The same furious mad dog was on June 4 made to bite still another refractory and another control dog. On June 6 the furious dog which had been utilised on June 3 and 4 died. The bulb was taken out and inoculated, after trephining, into three refractory dogs and three control dogs. On June 10 another street mad dog, having been secured, was, by the commission, made to bite one refractory and one control dog. On June 16 the commission have two new dogs, a refractory one and a control one, bitten by one of the control dogs of June 1, which had been seized with rabies on June 14 in consequence of the inoculation after trephining which it had received on June 1.

‘ On June 19 the commission get three refractory and three control dogs inoculated before their own eyes in the popliteal vein with the bulb of an ordinary street rnad dog. On June 20 they have inoculated in their presence, and still in a vein, ten dogs altogether, six of thern refractory and four just brought from the pound.

‘ On June 28, the Commission hearing that M. Paul Simon, a veterinary surgeon, had a furious biting mad dog, have four of their dogs, two refractory and two control dogs, taken to his place and bitten by the mad dog.

‘ The Rabies Commission have, therefore, experimented on thirty-eight dogs altogether — namely, nineteen refractory dogs and nineteen control dogs susceptible of taking the disease. Those of the dogs which have not died in consequence of the operations themselves are still under observation, and will long continue to be. The commission, reporting up to the present moment on their observations as to the state of the animals tried and tested by them, find that out of the nineteen control dogs six were bitten, of which six three have taken rabies. Seven received intra-venous inoculations, of which five have died of rabies. Five were trephined and inoculated on the brain ; the five have died of rabies.

‘ On the other hand, not one of the nineteen vaccinated dogs has taken rabies.

‘ In the course of the experiments, on July 13, one of the refractory doss died in consequence of a black diarrhoea which had begun in the first da s of July. In order to ascertain whether rabies had anything to do with it as the cause of death, its bulb was at once inoculated, after trephining, into three rabbits and one guinea-pig. All four animals are still to-day in perfect health, a certain proof that the dog died of some common malady, and not of rabies.

‘ The second report of the Commission will be concerned with the experiments made as to the refractoriness to rabies of twenty dogs to be vaccinated by the Commission themselves.’

M. Pasteur then announced that he had just received that same morning the first report addressed to M. Failures by the Official Commission on Rabies. It states that twenty-three refractory dogs were bitten by ordinary mad dogs, and that not one of them had taken rabies. On the other hand, within two months after the bites, QQper cent, of the controldogs similarly bitten had already taken the disease.)

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Pasteur’s Communications on Rabies: No. 6

October 26, 1885.— A Method for the Prevention of Rabies after the Bite of a ...

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