194 The Descent of Man. Paut 1, 



stales 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 origin- 

 ally brought from various parts of Africa and accustomed to the 

 climate of the West Indies. That acclimatisation plays a part, 

 IB shewn by the many oases in which negroes have become some- 

 what 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 during 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 acclimatisation, implies exposure during a 

 prodigious length of time ; for the aborigines of tropical America 

 who have resided there from time immemorial, are not exempt 

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

 there are districts in Northern Africa which the native inhabit- 

 ants are compelled annually to leave, though the negroes can 

 remain with safety. 



That the immunity of the negro is in any degree correlated 

 with the colour 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 between complexion 

 and a tendency to consumption, the conjecture seemed to me 

 not improbable. Consequently I endeavoured, with but little 

 success,'^' to ascertain how far it holds good. The late Dr. 



*"' Qnatrefiiges, ' Unite de I'Espfece " is some limited degree of relation 

 Humniiie,' 1861, p. 205. Waitz, " between the colour of the races of 

 * Jntroduct. to Anthropology,' trans- *' man and the climate inhabited by 

 lat. vol. i. 1S63, p. 124. Living- "them; the following invostiga- 

 stone gives analogous cases in his " tion seems worth consideration. 

 ' Travels.* *' Namely, whether there is any re- 

 in the spring of 1862 I ob- " lation in Europeans between the 

 tained permission from the Director- "colour of their hair, and their 

 General of the Medical department " liability to the diseases of tropical 

 of the Army, to transmit to the " countries. If the surgeons of the 

 Burgeons of the various regiments " several regiments, when stationed 

 on foi'eign service a blanli tabic, " in unhealthy tropical districts, 

 with the following appended re- " would be so good as first to count, 

 mnrks. but I have received no re- " as a standard of comparison, how 

 turns. " As several well-marked " many men, in the force whence 

 " cases have been recorded with *' the sick are drawn, have daj'k 

 " our domestic animals of a relation " and light-coloured hair, and hair 

 " between the colour of the dermal " of intermediate or doubtful tints: 

 " appendages aLd the constitution ; " and if a similar account were 

 "and it beiag notorious that Ihei'e '■ kept by the same medical i;eutl(!> 



