1881.] Human Complexion and its Causes. 279 
put in a white can. Just the same is the case with light. 
We call a surface white when it reflects all the incident rays, 
and black when it absorbs them all. We are not aware that 
the difficulty has ever been fairly met — why a colour should 
be advantageous for the skin in a hot climate, when for 
everything else which we wish to preserve from overheating 
it is found disadvantageous. 
To proceed : Mr. Buchan contends that in an arCtic 
climate transudation is accelerated. “ The frosty air, raised 
in temperature many degrees by contact with the body, be- 
comes very dry, and greedily drinks up its moisture. ” Thus 
the temperature of the system is lowered, and at the same 
time the person suffers from excessive thirst. Hence a very 
thick skin will be needful, which, though containing little 
pigment, will produce a swarthy effect. 
By a “ moist temperate ” climate the author means one 
like that of Western Europe, where the range of tempera- 
ture is small and the air contains a large amount of water 
in solution. Here perspiration is reduced by the inability of 
the atmosphere to take up much moisture. The cuticle is 
constantly thin, and the complexion clear and fair. In 
“ dry temperate climates ” the air is usually dry, the 
summers hot, and the winters severe. Hence a thick cuticle 
is needed “ to prevent the too rapid withdrawal of the fluid 
contents of the capillaries by the dry air,” whilst the pre- 
sence of a pigment “ suitable to the intensity of the sun’s 
rays ” produces various shades of yellow and brown. 
Under a “ humid tropical climate ” the author ranks such 
as have no dry season, with a high but steady temperature. 
The power of the sun’s rays will be so diminished by the 
abundance of vapour that the inhabitants will not require 
the protection of so dark a pigment as the natives of other 
tropical regions. A thin epidermis will be needed to facili- 
tate perspiration. Hence the natives of these equatorial 
regions should be distinguished by relatively fair com- 
plexions. In such tropical climates as are rainless, or 
possess well-marked dry seasons, the rays of the sun will 
descend with full power, whilst at the same time a consider- 
able degree of cold will be experienced before sunrise. To 
meet both these extremes a thick outer skin will be required, 
and we therefore find in such regions the blackest men and 
the thickest skins. 
A great part of the author’s contention must be at once 
conceded. In dry climates, whether cold or hot, and in 
such as undergo great vicissitudes of temperature, a thicker 
skin is undoubtedly required than in regions where the air 
