18 PROCEEDINGS OF THE CANADIAN INSTITUTE, 
the blood. This is conveyed to the air by minute ducts passing 
through the epidermis. It is obvious that, the less transparent the 
outer skin, the less light and heat will be transmitted to excite these 
glands into activity. In the second place, there is a continual 
transudation of sweat from the minute vessels of the surface of the 
body through the epidermis at every point. The thicker or more 
oily the scarfskin, the less will the amount of this transudation be. 
If it be both thick and oily, as in many dark races, the quantity 
transuded will be reduced to a minimum ; if it be thin and not oily, 
as in the fairest members of the white race, transudation will be 
copious. 
The amount of transuded sweat depends, however, not only on the 
thinness of the cuticle, but also on the degree to which the air in 
contact with the body is saturated with moisture; for there is a 
limit’ to the quantity of vapour which the air can absorb. This 
limit varies with the temperature, warm air absorbing more than 
cold. It is also to be remarked that perspiration relieves the body 
of heat as well as of moisture, and that a dark skin may serve as a 
means of radiating heat in climates in which a large loss of moisture 
is a disadvantage. Such being the nature of the skin, I now 
proceed to inquire what kind of it will best suit particular regions. 
For this purpose climates may be classified as— 
I. Aretie. 
II. Moist temperate. 
IIf. Dry temperate. 
IV. Moist tropical. 
V. Dry tropical. 
1. When the skin is exposed to great cold, perspiration by tran- 
sudation is accelerated. The frosty air, being raised many degrees in 
temperature by contact with the body, becomes very dry, and greedily 
drinks in its moisture. At the same time the body loses not only 
the heat which the air carries off, but also that which is rendered 
latent by the evaporation of the sweat. As a protection against the 
injury which a too rapid loss of perspiration and heat may inflict in 
an arctic climate, a thick integument is desirable. It is, I believe, 
the fact that arctic races have thick skins. At any rate M. de Quatre- 
fages says that cases of dry rough skins occur most frequently among 
the polar tribes. This I take to be a result of the thickness of the 
