RELATION OP PATHOGENIC TO SEPTIC BACTERIA. 59 



a necessary conclusion, that this insusceptibility must depend 

 both on the mice as well as on a change in the bacillus. 



I have made several series of observations, to be detailed at 

 a future period, by cultivating Bacillus anthracis in acid 

 pork broth, and to my great surprise the first cultivation, and 

 also sometimes the second cultivation, of blood Bacillus an- 

 thracis in this acid pork broth formed spores, and consequently 

 killed all mice when inoculated into them in infinitesimal doses ; 

 but as cultivation was carried on into a third and fourth, the 

 bacillus, although still copiously and typically growing during 

 the first four or five days, nevertheless did not form spores at 

 any time. As a consequence it did not prove effective on 

 many mice; but it proved fatal on guinea-pigs and rab- 

 bits when inoculated into them in minimal doses. 



What has been said in the foregoing paragraphs, respecting 

 the effects of inoculating with a given cultivation of Bacillus 

 anthracis in neutral pork broth and in gelatine pork, applies 

 not only to the first or the second cultivation, but also applies, 

 in exactly the same manner and to exactly the same degree, to 

 the third, fourth, fifth, sixth cultivation, and even (as I have 

 proved by my own observation) to the twentieth or thirtieth 

 cultivation of the bacillus in like nourishing material. As 

 each new sample of sterile material is inoculated from a former 

 sample, a typical and copious growth of bacillus threads takes 

 place in it. If the material be pork broth, spores will not be 

 formed in it as long as the growth takes place undisturbed 

 below the surface of the liquid. And each successive sporeless 

 cultivation will after a few days (and always within a week or 

 two) lose its power to kill mice, though it will retain for about 

 two months the same power that preceding cultivations pos- 

 sessed of killing guinea-pigs and rabbits when inoculated into 

 them. 



If any of these cultivations of Bacillus anthracis in 

 neutral pork broth or gelatine pork are kept for several weeks, 

 it will be noticed, as described above, that the mass of bacilli 

 gradually diminishes in a conspicuous manner. On a former 



