/O Actual Races in History. 



second nature of acclimatization or naturalization. 

 The proverb maybe referred to here: "Custom 

 _ ,. _ is a second nature." But the custom we 



Radical 



Nature and speak of now is physical, physiological. 

 Racial j t reacts upon the structure and form, 



Nature. 



affecting the anatomy and morphology. 

 It explains, also, much of the special pathology 

 which distinguishes a race; that is to say, its liability 

 to disease. For suppose that a disturbing action 

 which is the cause of disease begins to work upon 

 a system. It may affect the common, radical ele- 

 ment in our human species; and then the same 

 disturbing cause will produce radically similar ef- 

 fects upon all human beings, notwithstanding their 

 racial differences. This we experience in certain 

 epidemics that spare no races. But if this disturb- 

 ing action is spent upon the acquired and special 

 element in a race, the same cause will not produce 

 the same effects in different races, and the disease 

 will be more or less peculiar to certain groups. 

 Thus the European is singularly susceptible of 

 marsh fevers, to which, on the other hand, the con- 

 stitution of the negro is very indifferent. But, in 

 moist atmospheres, the negro is observed to be 

 very liable to consumption, while the European 

 enjoys a comparative immunity. 



81. Obviously there are some variations which 

 ,..,. . w , are quite normal in our climatic condi- 



A lliated Con* ... 



ditions of tions, as certain varying degrees of mois- 

 Life * ture or dryness, of heat or cold. But 



