400 THE HUMAN SPECIES 



cholera, enteric, leprosy, influenza, whooping cough, relapsing 

 fever, inflammation of the lungs, dysentery, gonorrhoea, soft 

 sore, lues, measles, rubeola, chicken-pox, typhus, scarlet fever, 

 Madura-foot, Malta fever, the various forms of malaria and 

 sleeping sickness. 



All other infectious diseases are common to man and 

 animals, or the latter are altogether immune. Man, on the 

 other hand, is immune to certain animal infections, e.g., swine 

 erysipelas, swine fever, rinderpest, fowl, cholera, etc. 



Between the different races of men there exists a consider- 

 able difference in relative, or absolute, immunity against certain 

 infections. 



No race is immune to cholera ; it is most fatal among 

 negroes. In the same way enteric, bubonic plague, tuberculosis 

 and diphtheria attack all men alike. The Malagese, the South 

 African negro races, and also the inhabitants of Iceland and 

 Greenland are almost entirely immune to syphilis. Only 

 negroes and Mongolians possess an immunity against yellow 

 fever; negroes lose their immunity little by little from child- 

 hood upwards, if, after a journey into the north of the United 

 States, they return into the yellow fever zone. No race is 

 immune against the acute exanthemata ; negroes are most 

 sensitive to small-pox. Finally, if cancer is to be included 

 among the infectious diseases, we must conclude that in Tunis 

 and Abyssinia, where it is less known, that the people are 

 completely immune to it, and that this immunity is passed on 

 from one generation to another. 



The general question of immunity, its hereditary transmis- 

 sion, and the part it plays in the life-histories of men and animals, 

 has been very clearly dealt with by Grober. 1 The great change 

 in the intensity of contagious diseases, their gradual loss of viru- 

 lence, and often their complete extinction, is a phenomenon 

 which may be explained from various points of view. Bacteri- 

 ologists are inclined to attribute it to loss of virulence in the 

 exciting cause ; clinicians think either that the sensitive indi- 

 viduals may have died out, or assume a congenital or acquired 

 immunity for the survivors, as for example, with plague, 

 cholera and influenza. The occurrence of immunity is attri- 

 1 J. Grober, "Die Vererbung der Immunitat," Med. Klinik, 1905, 18, p. 429. 



