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PHYSIOLOGICAL PATHOLOGY. 
immediately amputated that organ, with the thermo-cautery, be¬ 
low the point of inoculation, and in every instance rabies followed. 
Still, thermo-cauterization leaves no true wound ; all the divided 
structure is burned. 
I hasten these remarks in order to reach a part of the subject 
which most of all deserves our attention. 
The Academy has not forgotten that the discovery of the at¬ 
tenuation of viruses, in connection with its applications, which have 
been employed for the prophylaxy of certain diseases, has thrown 
much light on this capital fact of the possible experimental pro¬ 
duction of various degrees of virulency for a single virus. 
Rabies is pre-eminently a virulent disease, and the nature and 
effects of its virus are possessed with qualities so mysterious that 
the desire becomes natural and irresistible to ascertain whether 
the rabid virus may not also be capable of exhibiting various de¬ 
grees of propagating power. Our experience now authorizes an 
affirmative answer to this question. Without referring to various 
methods which are still the subjects of study and experiment, we 
have found that rabid virus, passing through various species 
of animals, is more or less modified in its virulency. Rabbits, 
guinea pigs, fowls and monkeys are susceptible of rabies. When, 
by successive transfers, the virus has reached a certain point of 
fixity peculiar to each species, the virulent power of the matter is 
far from being the same in all, differing notably from that of 
the canine subject, the virulency of which has regulated itself by 
numerous transmissions from dogs to dogs, from time immemo¬ 
rial. Spontaneous rabies finds no place in my convictions. 
We certainly have a virus which communicates rabies to the 
rabbit in seven or eight days, with such a degree of certainty 
that we are enabled by guess, so to speak, to name the duration 
of the incubation, determined by a change in the temperature or 
the appearance of the first external symptoms of the disease. 
We also have a rabid virus which communicates the disease to 
pigs in five or six days with no less certainty in* respect to the 
duration of its incubation. 
Before that point of fixity of which I have spoken has been 
reached in the various species of animals, each for itself, the 
