THE RAGES OF MAN. 221 



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 

 accustomed to the climate of the West Indies. That 

 acclimatization plays a part is shown by the many cases in 

 which negroes 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 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 acclimatization, 

 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 Rev. H. 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 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, nerv- 

 ous system or other tissues. Nevertheless, from the facts 

 above alluded to and from some connection apparently ex- 

 isting between complexion and a tendency to consumption, 

 the conjecture seemed to me not improbable. Conse- 

 quently I endeavored, with but little success, f to ascertain 



* Quatrefages, " Unite de I'Espece Humaine," 1861, p. 205. Waitz, 

 "Introduct. to Anthropology," translat., vol. i, 1863, p. 124. Liv- 

 ingstone gives analogous cases in his " Travels." 



f In the spring of 1862 I obtained permission from the Director- 

 General of the Medical Department of the Army to transmit to the 

 surgeons 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 relation between the color of the dermal 

 appendages and the constitution; and it being notorious that there is 

 some limited degree of relation between the color of the races of man 

 and the climate inhabited by them; the folio wing investigation seems 

 worth consideration. Namely, whether there is any relation in Euro- 

 peans between the color of their hair and their liability to the diseases 

 of tropical countries. If the surgeons of the several regiments, when 

 stationed in unhealthy tropical districts, would be so good as first to 



