SUGAR IN THE NUTRIENT MEDIUM. 161 



5. We inject for example, with the attenuated 

 bacillus cedematis maligni or anthracis another 

 variety which per se is almost entirely harmless for 

 example, bacterium prodigiosum. 



6. We inject the culture, mixed with an injurious 

 substance of non-bacterial origin for example, lactic 

 acid. In bacillus cedematis maligni this has pro- 

 duced increased pathogenic power, probably from 

 local impairment of the anti-bacterial activity of the 

 animal at the site of inoculation. 



The susceptibility of different species of animals 

 and of different individuals to different infectious 

 diseases varies from birth in a striking and not easily 

 explained manner. 



Certain species are absolutely immune against spe- 

 cial infection-producers.* For example, man against 

 rinder pest, the cow against glanders, and all ani- 

 mals which have been tested against syphilis, malaria, 

 and gonorrhoea. 



A series of other diseases is conveyed very rarely 

 and with difficulty to certain animals for example, 

 anthrax to certain varieties of pigeons, rats, and 

 sheep. This constitutes relative immunity. The 

 more vigorous and, as a general thing, the more 

 mature an animal is, the more completely is its rela- 

 tive immunity developed. Noxious influences of all 

 kinds (hunger, cold, excessive exertion, ingestion of 

 * It is especially remarkable that very closely allied varieties 

 often exhibit astonishing differences. For example, the glanders 

 bacillus can be conveyed very readily to the field mouse but not 

 to the house mouse ; the bacillus anthracis kills the house mouse 

 with almost absolute certainty and is hardly pathogenic to the rat. 

 Micrococcus tetragenus is pathogenic to the white variety of the 

 house mouse, but is not virulent to the gray variety. 

 11 



