58 DR. E. KLEIN. 



some mice, proved under all conditions and for a considerable 

 length of time, fatal to guinea-pigs and rabbits, no matter 

 whether spores had developed in it or not. This different be- 

 haviour of mice on the one hand and guinea-pigs and rabbits 

 on the other, towards an artificial cultivation of Bacillus 

 anthracis without spores, came indeed after a while to be a 

 useful means to decide whether a given cultivation of Bacillus 

 anthracis, after several days' incubation, contained spores or 

 not. I have so often repeated the following experiment that I 

 am confident it can serve as a typical one. A sample of a cul- 

 tivation of Bacillus anthracis in neutral pork broth, which 

 appears to the unaided eye a typical growth, and in which cul- 

 tivation the bacillus mass is left quiet at the bottom of the test 

 tube or flask for a week or two, when examined under the 

 microscope does not contain any spores. Inoculate with it 

 half-a-dozen mice and half-a-dozen guinea-pigs or rabbits. All 

 or most of the mice will probably remain well, all the guinea- 

 pigs and rabbits die within forty-eight hours. Allow the 

 bacillus of the above cultivation to form spores, by sowing 

 them on to gelatine pork, and keeping them well exposed to 

 the surface, or establish a new cultivation in neutral pork 

 broth, and now inoculate the above six mice, or as many other 

 mice as you like, with this new cultivation in its early stage or 

 with the above spores, every one of them will be probably dead 

 within thirty-six or forty-eight hours. 



The conclusions to be drawn from this seems to me obvious. 

 Mice, unlike guinea-pigs and rabbits, are insusceptible to the 

 Bacillus anthracis when cultivated artificially in neutral 

 pork, after this cultivation has been kept for some time, pro- 

 vided no spores are formed in the bacilli. But no immunity 

 of any kind is by such inoculation conferred on the mice. 

 Since mice are very susceptible to the Bacillus anthracis 

 of the blood and tissues of an anthrax animal in which noto- 

 riously no spores occur, and since they are (equally with 

 guinea-pigs and rabbits) susceptible to the spores of the arti- 

 ficially cultivated Bacillus anthracis and to the bacillus of 

 a fresh cultivation, it seems to me it follows from the facts^ as 



