90 Manual of Veterinary Microbiology. 



ties of charbonous blood in such a manner that all the 

 bacilli were influenced to the same extent; the de- 

 gree of eufeeblement, in fact, depends on the temper- 

 ature and the duration of the heating. Chauveau has 

 prepared two vaccines, intended to be inoculated in 

 succession : the first, the least active, is obtained by 

 heating defibrinated blood at 50° during fifteen min- 

 utes ; the second, by heating the same liquid at the 

 same temperature during nine to ten minutes. This 

 last vaccine inoculated to animals which have not re- 

 ceived the first may yet cause the death of some in- 

 dividuals. 



To obtain a uniform result with charbonous blood 

 it is necessary always to use fresh blood in which the 

 bacilli are free from spores. These latter are endowed 

 with a much greater power of resistance and are not 

 attenuated like the bacilli; hence, in his researches 

 upon the attenuation of cultures, M. Chauveau first 

 cultivated the bacteridia at a temperature of 42° to 

 43°, in order to prevent the formation of spores. The 

 asporogenous bacteridia are heated to 47° during three 

 consecutive hours; they are then attenuated to the 

 extent that they no longer kill adult guinea pigs. 

 Brought then to the favorable vegetating tempera- 

 ture of 37° the attenuated bacteridia form spores ; but 

 these are liable when placed under suitable conditions 

 to produce virulent bacilli again. 



In order to render attenuation transmissible to suc- 

 cessive generations of bacteridia M. Chauveau then 

 brought the sporulated cultures to temperatures 

 neighboring on 80°. The attenuation then became 

 fixed upon the spores and the latter, returned into 

 nutritive bouillon at 37°, produces bacilli attenuated 



