102 PHILOSOPHY OF ZOOLOGY. 
peculiar secretions, and the purposes which these serve in 
the animal economy. One class of these secretions performs 
the office of lubricating the skin ; another of regulating the 
temperature of the body ; and a third of carrying off the 
superfluous carbon. 
As the skin forms the external covering of the body, 1t is 
therefore exposed to the decomposing influence of the at- 
mosphere or the waters. Were no remedy provided, its 
texture would soon be destroyed; by desiccation in the 
one case, and maceration in the other. But, for the pre- 
vention of these effects, the skin is liberally supplied with 
vessels, which secrete upon its surface, fluids, varying in 
their nature, according to the wasting agents which act 
upon it. ‘They may, however, be divided into two kinds ; 
the unctuous and the viscous; on the nature of which, we 
shall offer a few observations. 
1. Unctuous Secretions. —These are confined to animals 
which have warm blood and the cells of the cellular web 
filled with fat, as mammalia and birds. 
An oily matter js secreted from the whole skin of mam- 
mala, in a manner not very satisfactorily determined. It 
coats, likewise, the hairs, and serves to prevent the air from 
drying these parts too much, or the water from wetting them. 
{t keeps the skin of the whale so soft and smooth as to ap- 
pear like oiled silk ; and the seal, and other aquatic mam- 
malia, emerge from the water with their fur as dry as if 
they had been executing their movements on land. 
In some cases, the glands which secrete an unctuous 
matter, are numerous in particular places, and their open- 
ings become obvious to the eye, as in the human nose, and 
below the under lip, from which the greasy matter may be 
squeezed, like little worms. ‘These glands are likewise nu- 
merous in the arm-pits; and, in many quadrupeds, they 
oceur i little bags near the anus. In birds they unite, 
