PATHOLOGICAL PHYSIOLOGY. 
27 
shows itself again less virulent than it was at first towards 
rabbits. 
In these new conditions, it gives to rabbits a disease sponta¬ 
neously curable, and, moreover, renders the animal, when recov¬ 
ered, refractory to the mortal microbe of a rabbit. Hence this 
important conclusion; that the habit once acquired by continued 
lodgement in a species (as the guinea pig) and which corresponds 
to a given virulency, may change this property as it relates to 
another specie (the rabbit), and so diminish it as to render it a 
proper vaccine for the latter species. 
This result is of an importance which cannot escape the at¬ 
tention of any observer, for it contains the secret of anew method 
of attenuation which can be applied to some of the most viru¬ 
lent forms of virus. Allow me to give you an example and an 
explanation : 
Here are the very curious results of the inoculations of hog 
cholera, made upon pigeons on one hand and upon rabbits on 
the other. 
If one inoculates the microbe of hog cholera in the pectoral 
muscle of a pigeon, the bird dies in six or eight days, after pre¬ 
senting the external visible symptoms of chicken cholera. 
When the blood of this first pigeon is inoculated to a second, 
the blood of this one to a third, and so on, the microbe acclima¬ 
tizes itself in the pigeous. The symptom of ball shape, the 
sleepiness, habitual manifestations of the disease, appear in much 
less time than in the first animals of the series. Death also 
becomes more rapid ; and again the blood of the last pigeons is 
much more virulent for swine than the most infectious products 
taken from an animal that has died from spontaneous disease. 
The passage of the microbe of hog cholera in rabbits brings 
us to another result. The infectious products of a pig that has 
died from the disease, or their cultures, inoculated to rabbits, 
always produce sickness and most generally death. 
If hog cholera is inoculated from rabbit to rabbit, the microbe 
becomes acclimatized in them. All the animals die in a few days- 
The cultures of the blood of these rabbits in these sterilized media 
becomes gradually easier and more abundant. The microbe itself 
