Nothing la more variable than the natural period of inonbation in this disease. One dog goes mad in four or six weeks, another in two or three months. By one method of inter-cranial inoculation, the period of incubation is shortened and known approximately. The duration of incubation may also depend upon the quantity of active virus reaching the nervous system unchanged. The quantity of virus may be infinitesimal.

On May 10th., 1882, ten drops of a fluid, obtained by macerating, in a sterilized broth, a portion of the bulb of a wandering mad-dog, were introduced into the popliteal veln of a dog. A second dog was inoculated with one one-hundredth, and another dog one two-hundredth of the quantity. The first dog had rabies on the eighteenth day, the second on the thirty, fifth, and the third was unaffected, the quantity of virus not being sufficient. This dog was again tested and contracted rabies twenty-two days later. if we operate by trephinlng we obtain a method certain in its effeet. If we take mad dogs at any season, and in each case isolate the bulb and inoculate with the material by trephining a few rabbits, the phenomena will be regular. No metier what dog be used the incubation will fall within twelve or fifteen days; it will never be eleven, ten, or eight days though it may be over fifteen days. Other instances of the peculiarities of the virus might be given, all proving that there exists and can be produced different kinds of rabies all more or less violent and fatal.

Guinea pigs soon attain a maximum of virulence; the incubative period is shortened, and by transmission we obtain a virus which surpasses in virulence that of rabies ordinarily met with.

Jenner propounded the theory that poison called "grease" in the horse, now described more correctly as the horse-pox may be weakened in activity by transmission through cows. This idea of Jenner's struck us as being capable of imitation. Could we attenuate the virus by passing it through the bodies of certain animals? Many attempts were made, until in the case of monkeys, a medium was found.

December 6,1883, the bulb of a dog which had been bitten by a child who died of hydrophobia, was taken and a monkey inoculated by trephining. In eleven days the monkey became rabid. From this monkey, the virus was transmitted to a second. In eleven days the second showed signs of rabies. A third monkey became rabid in twenty-three days. Other monkeys were experimented on. With the bulb of each of these monkeys two rabbits were inoculated by the method of trephining. The rabbits infected by the first monkey became rabid on the thirteenth and sixteenth days; the two from the second monkey on the fourteenth and twentieth days; the two from the third monkey on the twenty-sixth and thirtieth days; two from a fourth monkey on the twenty-eighth day in each case; two from a fifth monkey on the twenty-seventh day in each case; two from a sixth monkey on the thirtieth day in each case.

By transmission from monkey to monkey, and from monkey to rabbits, the strength of the poison seemed weakened. A dog inoculated with the bulb of the fifth monkey had incubation period of not less than fifty-eight days; other experiments confirmed these results. We thus found out a method of attenuating the virus, and a method of vaccinating dogs as prevention against rabies.

As a starting point we take one of the rabbits inoculated from monkeys to such a degree, that hypodermic or intravenous injection does not cause death. The preventive inoculations are done with the bulbs of rabbits which have been successfully infected from monkeys to rabbits. Jenner's methods met with opposition. Remembering this I determined to lay my results before a scientific commission. M. Tallieres, Minister of Instruction in France, supported my project. M. Beclard, P. Bert, Bouley, Tisseraud, Villemin, and Vulpian were appointed to examine my statements and check the facts I had communicated to the Academy of Sciences May 29, 1884. M. Bouley was chosen President, and Villemin, Secretary. The committee have recently presented their report to the Minister. I am now able to give a brief account of the first report.

I presented to the committee nineteen vaccinated dogs, all of whom had been rendered insusceptible by preventive inoculation, and thirteen of these had been further tested after vaccination by inoculation by trephining.

These nineteen dogs were compared in various ways with nineteen other dogs chosen for the purpose of experiments. On June 1st. two of the protected dogs and two trial dogs were inoculated by trephining under the dura mater with the bulb of a mad dog. On June 3d. one protected dog and one trial dog were bitten by a mad dog. On June 4th. the same mad dog bit another protected and another trial dog. June 6th. the mad dog used June 3d. and 4th. died, and the bulb was inoculated by trephining on three trial and three protected dogs.

June 10th. one protected and one trial dog were bitten by another mad dog obtained from the streets; June 16th. one protected and one trial dog were bitten by a dog which had gone mad June 14th. as a result of the experiments; June 19th. three protected and three trial dogs inoculated in popliteal veins with bulb of mad dog; June 20th. six protected and four trial dogs inoculated in vein; June 28th. two protected and two trial dogs bitten by mad dog at the hospital of M. Paul Simon, a veterinary surgeon.

Now Let Us Look At The Results

The Com. performed experiments on thirty-eight dogs, nineteen protected and nineteen not protected. They report that in the case of the nineteen trial dogs, rabies occurred as follows: - of six bitten, rabies occurred in three; of seven inoculated in vein, rabies in five; of five trephined, all died. Trephining was the surest. On the other hand, not a single symptom of rabies appeared in any of the dogs vaccinated by me and declared insusceptible; one dog died from diarrhoea, the cause of death being verified by post-mortem and also by tests. Three rabbits and one guinea pig were inoculated with the bulb of this dog and are in the best of health. The animals are still under observation".

The following is a literally translated extract from the address of M. Bouley, before the French Association for Advancement of Sciences.