242 INFECTION AND IMMUNITY 



to glanders, anthrax, and even tuberculous infections, to which herbiv- 

 orous animals are markedly susceptible. 4 It is likely, too, that the 

 great differences between animals of various species in their metab- 

 olism, temperature, etc., may call for special cultural adaptation on 

 the part of the bacteria. The fact that the bacillus of avian tuber- 

 culosis whose natural host has a normal body temperature of 40 C. 

 and above will grow on culture media at 40 to 50 C., whereas B. 

 tuberculosis of man can not be cultivated at a temperature above 

 40 C., would seem to lend some support to this view. The difference 

 between warm- and cold-blooded animals has already been noted. The 

 necessity for cultural adaptation, too, would seem to be borne out 

 by the great enhancement observed in the virulence of certain micro- 

 organisms for a given species after repeated passage through in- 

 dividuals of this species. 



RACIAL IMMUNITY. Just as differences in susceptibility and im- 

 munity exist among the various animal species, so the separate races 

 or varieties within the same species may display differences in their 

 reactions toward pathogenic germs. Algerian sheep, for instance, 

 show a much higher resistance to anthrax than do our own domestic 

 sheep, and the various races of mice differ in their susceptibility to 

 anthrax and to glanders. 



Similar racial differences are common among human beings. As 

 a general rule, it may be said that a race among whom a certain 

 disease has been endemic for many ages is less susceptible to this dis- 

 ease than are other races among whom it has been more recently 

 introduced. The appalling ravages of tuberculosis among negroes, 

 American Indians, and Esquimaux, bear striking witness to this fact. 

 Conversely, the comparative immunity of the negro from yellow fever, 

 a disease of the greatest virulence for Caucasians, furnishes further 

 evidence in favor of this opinion. It must not be forgotten, however, 

 in judging of these relations, that the great differences in the customs 

 of personal and social hygiene existing among the various races may 

 considerably affect the transmission of disease and lead to false con- 

 clusions. 



In so far as the statement made above is true, however, it seems 

 to indicate that the endemic diseases have carried in their train a 

 certain .degree of inherited immunity. 



' Hahn, in Kolle und Wassermann, vol. iv. 



