104 PHILOSOPHY OF ZOOLOGY. 
of phosphate of lime and oxide of iron. But when procured 
by this method, it is impure, being mixed with the fat of 
the unctuous secretions. 
When the body is subjected to violent exercise, or expos- 
ed to a hot atmosphere, the sweat becomes visible to the 
eye like drops of dew, at the pores from which it issues. 
In this state, it is fluid like water, but has a perceptibly 
saltish taste. Brrzesius collected a few drops of sweat, 
as they fell from his face, and evaporated them carefully. 
** The yellowish residue had all the appearance under the 
microscope, of the usual mixtures of potash and soda, with 
lactic acid, lactate of soda, and its accompanying animal 
matter. It reddened litmus, and dissolved in alcohol ; 
and was, without doubt, of the same nature as the analo- 
gous matter found in the other fluids.” 
From the circumstance, that the quantity of sweat per- 
spired, is im proportion to the temperature, being scarcely 
perceptible when the surface of the body is disagreeably 
cold, but copious when heated to excess, it has been con- 
cluded, that this secretion is intended to regulate the degree 
of animal heat, and prevent its accumulation beyond cer- 
tain limits. The deficiency of perspiration in, the dog, is 
made up by the copious discharge cf saliva which takes 
place when the animal is heated by hard exercise. 
When the sweat reaches the surface of the body, it be- 
gins to evaporate ; and, as fluids, in passing to a state of va- 
pour, absorb a quantity of heat, the sweat abstracts caloric 
from the body, and reduces its temperature. "The cooling 
effect of evaporation, may be felt by any one, upon wetting 
a finger and exposing it tothe air. It will soon become cold- 
er than the others which were left dry. 
There is still another secretion which takes place from 
the skin, differmg from those which we have already enu- 
merated, and consisting in the emission of carbon. 
