52 INFECTION AND RESISTANCE 



form of local or general injury, infection can be accomplished. In 

 the case of protozoan diseases species adaptation is much more rigid 

 and parasites that infect one species are very often restricted en- 

 tirely to that class, heing unable to infect any other animal, even 

 though no striking difference in temperature or metabolism exists. 



We may convey the clearest conception of all such species differ- 

 ences by a tabulation of some of the more important infectious dis- 

 eases of man with a statement in each case concerning its transmissi- 

 bility to animals, as follows : 



Tuberculosis, human type, spontaneously infects man. It is very 

 often observed in monkeys kept in captivity. Cattle, swine, and 

 sheep are probably never spontaneously infected; guinea pigs are 

 highly susceptible to experimental inoculation. Cattle, swine, sheep, 

 and rabbits are relatively very resistant to experimental infection. 

 Dogs and goats are still more so. Birds seem to be entirely refrac- 

 tory. 



Tuberculosis, Bovine Type. Spontaneous infection occurs in do- 

 mestic animals, chiefly cattle ; it is less frequent in sheep, hogs, and 

 horses; it has been reported in dogs and goats. In man infection 

 does occur, but only a small percentage of human tuberculosis is of 

 the bovine type, and these cases are almost exclusively in children. 

 In tabulating 1,042 cases which have been carefully studied, Park 

 and Krumwiede 3 report the following figures : 



Cases of Tuberculosis in Man (1042) 

 Over 16 years 



Human type 677, bovine type 9. 

 5 years to 16 years 



Human type 99, bovine type 33. 

 Under 5 years 



Human type 161, bovine type 59. 



The large majority of bovine infections were abdominal or in- 

 volved cervical lymph nodes. 



Experimental infection is successful in rabbits and guinea pigs, 

 both of these animals succumbing more rapidly to this than to the 

 human bacillus. In fact, the relative resistance of rabbits to the 

 human bacillus is such that rabbit inoculation is one of the most 

 important methods of differentiating between the two types. Birds 

 are refractory. 



Tuberculosis of the avian type occurs spontaneously in birds. It 

 may be experimentally produced in rabbits (Strauss and Gamaleia). 

 Injected into cattle it causes a local reaction only. 



Tuberculosis of cold-blooded animals is not transferable to warm- 

 blooded animals. 



Syphilis spontaneously occurs in man only. It can be inoculated 



3 Park and Krumwiede. Jour, of Med. Res., Vol. 23, 1910. 



