Chap. VIL] THE RACES OF MAN. 235 



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 Rev. B. Tristram states that there are districts in 

 Northern Africa which the native inhabitants are com- 

 pelled annually to leave, though the negroes can remain 

 with safetv. 



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

 related 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 appar- 

 ently existing between complexion and a tendency to con- 

 % sumption, the conjecture seemed to me not improbable. 

 Consequently I endeavored, with but little success, 48 to 



48 In the spring of 1862 I. obtained permission from the Director- 

 General of the Medical Department of the Army, to transmit to the sur- 

 geons of the various regiments on foreign service a blank table, with the 

 following appended remarks, but I have received no returns : " As several 

 well-marked cases have been recorded with our domestic animals of a re- 

 lation between the color of the dermal appendages and the constitution ; 

 and it being notorious that there is some limited degree of relation be- 

 tween the color of the races of man and the climate inhabited by them, 

 the following investigation seems worth consideration, namely, whether 

 there is any relation in Europeans between the color of their hair and 

 their liability to the diseases of the tropical countries. If the surgeons 

 of the several regiments, when stationed in unhealthy tropical districts, 

 would be so good as first to count, as a standard of comparison, how 

 many men, in the force whence the sick are drawn, have dark and fight 

 colored hair, and hair of intermediate or doubtful tints ; and if a similar 

 account were kept by the same medical gentlemen of all the men who 

 suffered from malarious and yellow fevers, or from dysentery, it would 

 Boon be apparent, after some thousand cases had been tabulated, whether 

 there exists any relation between the color of the hair and constitutional 

 liability to tropical diseases. Perhaps no such relation would be discov- 

 ered, but the investigation is well worth making. In case any positive 

 result were obtained, it might be of some practical use in selecting men 

 for any particular service. Theoretically the result would be of high 



