CHOLERA OF FOWLS. 289 



previously in certain organs, has passed into the 

 blood and increases there, we observe that what- 

 ever may have been the original virulence of the 

 virus at the time of inoculation, that taken from 

 the blood of the dead fowl has a considerable viru- 

 lence and kills ordinarily ten times out of ten, 

 twenty out of twenty." l When an interval of 

 three to eight months is allowed to elapse between 

 successive cultures, the virulence is modified more 

 or less according to the length of time. But each 

 degree of attenuation may be preserved through 

 a series of cultivations made at short intervals 

 (Pasteur). It is necessary to cultivate the micro- 

 coccus in contact With the air as it is aerobic. In 

 Salmon's experiments it was observed to form a 

 mycodenna upon the surface of the culture-fluid. 

 The last-named observer states that the micro- 

 cocci are not abundant in the blood of a fowl, 

 drawn from a vein during life, but that they are 

 more abundant in blood taken from the body after 

 death. Putrefaction destroys the potency of viru- 

 lent fluids. The thermal death-point of the micro- 

 coccus has been fixed by Salmon as somewhere 

 between 124 and 140 Fahr. Of three fowls in- 

 oculated with virulent blood heated to 124 for 

 fifteen minutes, two died ; while two fowls inocu- 

 lated with blood that had been heated to 140 for 

 the same time, remained in good health ; one was 

 subsequently proved to be susceptible by inocula- 



1 Comptes rendus XCI., p. 375. 

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