INFECTION AND IMMUNITY. 415 



comprises the " septicaemias," and of them the disease of 

 animals known as anthrax represents a type of the 

 condition. If the cadaver of an animal dead of anthrax 

 be examined by bacteriological methods it will be dis- 

 covered that there is present in all the organs and 

 tissues an organism, a bacillus, of definite form and 

 biological characteristics ; and if the organs, and tissues 

 generally, be subjected to microscopic examination this 

 same organism will be found always present and always 

 located within the capillaries. At many points it will 

 be seen crowded in the capillaries in such numbers as 

 to almost, if not quite, burst them, and very commonly 

 their lumen for a considerable extent is entirely occluded 

 by the growing bacilli. In such a case as this we might 

 be tempted to conclude that death had resulted from 

 mechanical interference with the capillary circulation. 

 Suppose, however, we subject the cultures obtained from 

 this animal to conditions, either chemical or thermal, 

 that are not particularly favorable to their normal 

 development, and from time to time inoculate sus- 

 ceptible animals with the cultures so treated. The' 

 result will be that, as we continue to expose our cultures 

 to unfavorable surroundings, the period of time that is 

 required for them to cause the death of animals will, 

 in some cases, gradually become extended, until finally, 

 death will not ensue at all after inoculation. If, as 

 these animals die, a careful record of the conditions 

 found at autopsy be kept and compared, it will ulti- 

 mately be noticed that the animals that die a longer time 

 after inoculation present conditions more or less at 

 variance with those seen in the original animal that died 

 more quickly after having been inoculated. These 

 differences usually consist in a diminution of the num- 



