124 EXPERIMENTAL EVOLUTION LECT. 



for some reason or other, much less to fear from malaria 

 than the " white devils." The same difference is found 

 concerning tuberculosis : while it is more dangerous 

 for Polynesians and negroes than for whites, it is more 

 deadly for the whites than for the Mongolians, among 

 whom it has been said that Thibetans quite escape 

 the disease. The statement may have been exagge- 

 rated : at all events, it shows that the yellow race enjoys 

 comparative immunity from tuberculosis. Similar 

 instances are frequent among animals : not only do we 

 meet with instances of diseases which are peculiar to 

 some species only, 1 but within the same species some 

 breeds enjoy immunity while others do not. For in- 

 stance, Prof. Chauveau has shown that the sheep 01 

 Algeria enjoy a much greater immunity in respect to 

 anthrax than those of France, and the same differ- 

 ence obtains among asses. This is a racial character, 

 for foreign breeds living in Algeria do not acquire it ; 

 but the Algerian breeds transferred into Europe seem 



1 For instance, anthrax affects sheep especially, while it is scarcer 

 among oxen, hogs, and horses, and is never met with among birds. To 

 glanders the pigeon seems to be the only bird at all susceptible. 

 Syphilis is peculiar to man, though it possibly may be seen in apes 

 and hogs. Rats and mice enjoy an almost perfect immunity from 

 diphtheria, and any number of similar cases may be found in any text- 

 book on Bacteriology. Perfect immunity is rather doubtful, but it is 

 quite certain that many virulent diseases, due to microbes, exist spon- 

 taneously only in a limited number of species, but may be conferred 

 experimentally upon some or many others under experimental condi- 

 tions. 



