3o8 CLASSICS OF MODERN SCIENCE 



Rabies, whether in dog, man, horse, ox, wolf, fox, etc., 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 authenti- 

 cated 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 Hfe. It would be quite as well, against the assertion that 

 an oak tree always proceeded from another oak tree, 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 the 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 vary- 

 ing 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 caress- 

 ing rabies, for such do exist, 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 were 

 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, is 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 it- 

 self, and at other times aborts completely ; but inoculations on the 

 brain are never sterile, and give the disease after a relatively short 

 incubation. 



