104 rini.osoriiY 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. BEKZELIUS 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 wasj 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 in 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 of 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 to the 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, differing from those which we have already enu- 

 merated, and consisting in the emission of carbon. 



