28o C H A P T i; R 48, 
part of the fkin which appears black in 
Negroes, is the corpus reticulare cutis^ and 
external lamella of the epidermis. 4, That 
the colour does not proceecj from any black 
humour or fluid parts contained in their 
fkins. 5. That the epidermis ^ efpecially its 
external lamella^ is divided into two parts, 
by its pores and fcales, 200 times lefs than 
the particles of bodies, on which their co- 
lours depend. Hence Dr. Mitchell con^ 
eludes, that the proximate caufe of the 
colour of Negroes is threefold ; viz. the 
opacity of their fkins, proceeding from the 
thicknefs and denfity of the texture, which 
obftruds the tranfmiflion of the rays of 
light frorn the white and red parts below 
them ; together with their greater refrac- 
tive power, which abforbs thofe rays ; and 
the fmallnefs of the particles of their Ikins, 
which hinder them to refledl any light." 
After which, he difcourfes op the influence 
of the fun, and the modes of life among the 
inhabitants of hot countries, as the remote 
caufes of the colour of Negroes and In-, 
flians. 
Dr. Mitchell returned to Engla7id, I 
believe. 
