382 On the Skin in the Dark Traces of Mankind. 



having ivory black rubbed on its inner surface ; on bringing 

 the themiometer into the sun''s rays, the column of liquid de- 

 scended rapidly in the stem, the ball of which was covered 

 with the blackened cuticle. 



It is evident, from the result of experiments which I have 

 related, that a much less degree of heat can be borne when 

 the heat is applied locally, or so that the perspiratory process 

 is not excited over the whole system, than Sir Joseph Banks 

 and others were able to bear in heated apartments where per- 

 spiration was fully excited. 



This circumstance leads me to offer an explanation of the 

 functions, or, not to speak mincingly, of the uses served by the 

 peculiar colouring matter in the dark races. Blumenbach and 

 Dr Winterbottom concur in stating the Negro to perspire 

 more readily than the European or White, and Dr John Davy, 

 in the 3d vol. of the Medico-Chirurgical Transactions, gives 

 its due influence to this property. After noticing that the 

 excessive perspiration in dark people must keep down the tem- 

 perature, he proceeds, " In the inhabitants of the tropics, the 

 exhalant arteries of the skin seem unusually expanded, and the 

 whole apparatus peculiar to this secretion unusually developed ; 

 and I believe that the blood itself is less viscid, more fluid, and 

 flows more readily through the vessels, so as to promote per- 

 spiration, and by that means contributing to the cooHng of the 

 surface, and being cooled itself, it contributes again when it 

 flows back upon the heart, to the reduction of the temperature 

 of the internal parts." 



Were the inhabitant of the tropic not possessed of this or- 

 ganization, his system could not respond to the stimulus of 

 heat, by a determination of fluid to the surface of the body. 

 And the heat absorbed by the skin being prevented from en- 

 tering the system by the perspiratory process, the greater ra- 

 diating power of a dark skin must be beneficial in cooling. 



Again, the dark skin places the Negro in the conditions of 

 his climate by causing him to radiate heat at night, and be- 

 come at that time cooler than a White in the same circum- 

 stances. This is a fact which has been observed of the Ne- 

 groes. Their propensity for exercise in the open air at night 

 has been remarked. Thus we road that when the fleet of 



