THE DESCENT OR ORIGIN OF MAN 257 



fevers that prevail along at least 2,600 miles of the shores of 

 Africa, and which annually cause one-fifth of the white set- 

 tlers to die, and another fifth to return home invalided." 

 This immunity in the negro seems to be partly inherent, 

 depending on some unknown peculiarity of constitution, 

 and partly the result of acclimatization. Pouchet" states 

 that the negro regiments recruited near the Soudan, and 

 borrowed from the Viceroy of Egypt for the Mexican war, 

 escaped the yellow fever almost equally with the negroes 

 originally brought from various parts of Africa and accus- 

 tomed to the climate of the West Indies. That acclimatiza- 

 tion plays a part is shown by the many cases in which ne- 

 groes have become somewhat liable to tropical fevers after 

 having resided for some time in a colder climate. •" The 

 nature of the climate under which the white races have 

 long resided likewise has some influence on them; for dur- 

 ing the fearful epidemic of yellow fever in Demerara during 

 1837, Dr. Blair found that the death-rate of the immigrants 

 was proportional to the latitude of the country whence they 

 had come. With the negro the immunity, as far as it is the 

 result of acclimatization, implies exposure during a prodig- 

 ious length of time ; for the aborigines of tropical America 

 who have resided there from time immemorial are not ex- 

 empt from yellow fever; and the Eev. H. B. Tristram states 

 that there are districts in Northern Africa which the native 

 inhabitants are compelled annually to leave, though the 

 negroes can remain with safety. 



That the immunity of the negro is in any degree corre- 

 lated with the color of his skin is a mere conjecture : it may 

 be correlated with some difference in his blood, nervous 

 system, or other tissues. Nevertheless, from the facts above 

 alluded to, and from some connection apparently existing 



"* Major TuUoeh, in a paper read before the Statistical Society, April 20, 

 1840, and given in the "Athensum," 1840, p. 353. 



™ "The Plurality of the Human Race" (tranalat.), 1864, p. 60. 



«> Quatrefages, "Unite de rSsp^ee Humaine," 1861, p. 205. Waita, 

 ■"Introdnct. to Anthropology," tranelat., vol. i., 1863, p. 124. Liringstoaa 

 gives analogous oases in his "Travels." 



