242 BACTERIA IN INFECTIOUS DISEASES. 



favorable to their development. These conditions 

 doubtless relate mainly to the composition and 

 temperature of the culture-medium i.e., of the 

 blood of the animal and consequently vary in 

 different species of animals. But that the compo- 

 sition of the blood should be changed materially 

 and permanently in the same animal, as a result 

 of the mild form of disease which follows pro- 

 tective inoculation, it is difficult to believe. Yet 

 this is the explanation given by Pasteur of the 

 immunity afforded by such inoculations. This 

 change is supposed to consist in the removal of 

 some material essential for the nutrition of the 

 microbe, which is exhausted during the attack, 

 and never reproduced. This view is sustained 

 in the following language : 



" It is the life of a parasite in the interior of the body 

 which produces the malady commonly called ' cholera 

 des poulesj and which causes death. From the moment 

 when this culture (i. e., the multiplication of the para- 

 site) is no longer possible in the fowl, the sickness can- 

 not appear. The fowls are then in the constitutional 

 state of fowls not subject to be attacked by the disease. 

 These last are as if vaccinated from birth for this mal- 

 ady, because the foetal evolution has not introduced into 

 their bodies the material necessary to support the life of 

 the microbe ; or these nutritive materials have disap- 

 peared at an early age. 



" Certainly one should not be surprised that there 

 may be constitutions sometimes susceptible and some- 

 times rebellious to inoculation that is to say, to the 

 cultivation of a certain virus, when, as I have an- 



