Page:Popular Science Monthly Volume 25.djvu/389

Rh a mad dog, which, as I have just stated, lacks much of being of maximum potency, when transferred to the rabbit, must pass through the systems of several individuals before reaching its maximum.

A rational application of the results which I have just made known leads readily to the rendering of dogs insusceptible to rabies. We have learned that the experimenter may have at his disposal attenuated rabies-viruses of different strengths; some which are not fatal will protect the system from the effects of more active viruses, and the latter against those which are fatal. Let us take an example. Rabies-virus is obtained from a rabbit which has died from trepanning after a period of incubation which exceeds by several days the shortest time in which the disease may be induced in the rabbit. This invariably takes place within seven or eight days after inoculation by trepanning with the most potent virus. The virus from the rabbit in which the incubation has been long, is inoculated, by trepanning, into a second rabbit, and the virus from this one into a third. With each successive transfer, some of the virus, which becomes stronger and stronger each time, is inoculated into a dog, who becomes gradually more hardened against the operation of the poison, until he is finally found capable of withstanding a fatal virus. He then becomes entirely insusceptible to rabies, the virus of a mad dog producing no effect upon him, whether introduced by intra-venous inoculation or by trepanning. By inoculation of the blood of rabid animals, under certain conditions, I have succeeded in greatly simplifying the operations of vaccination, and in producing in the dog the most decided state of insusceptibility. I shall soon make known the details of the experiments on this point.

Until the time when rabies shall have become extinct through vaccination, the prevention of the development of this affection, in consequence of bites by rabid dogs, will be a problem of considerable interest. In this direction, the first attempts which I have made give me the greatest hopes of success. The period of incubation after biting is, I have every reason to believe, of such length that the subject may be rendered insusceptible before the fatal form of the disease develops. The preliminary experiments are very favorable to this opinion, but the tests must be infinitely multiplied on various species of animals before therapeutics will have the boldness to try this preventive on man.

Notwithstanding the confidence with which the numerous experiments I have made during the last four years inspire me, I do not announce the facts that point to a possible prevention of hydrophobia without some apprehension. Had I had sufficient material means, I should have preferred not making this communication till I had solicited, by the kindness of some of my associates of the Academy of Sciences and the Academy of Medicine, the verification of the conclusions I have just made known; and I have requested M. Faillières,