428 PHYSIOLOGY. 



When, however, the secretion of the glands is increased in quan- 

 tity or its evaporation arrested,, drops appear upon the skin. These 

 drops of water form what is commonly known as sveat. During this 

 condition the skin is also supple and soft, but is humid. There often 

 is, in fact, a visible liquid. 



Sweat is a more or less transparent liquid, of a salty flavor. It 

 is constantly acid in reaction and has a specific gravity of 1.004. 



The acidity is due to acid sodium phosphate. From its very 

 ready contamination, it is impossible to obtain sweat in a pure state. 



The relation of the sensible and insensible perspirations varies 

 considerably with the temperature of the air. In round numbers, 

 the total amount of sweat secreted by a man is two pounds in twenty- 

 four hours. 



The quantity of solid components of sweat is, on the average, 

 1.0 per cent. It may descend to 0.8 per cent, when there is an 

 increase in the rapidity of the secretion. That means that in pro- 

 fuse perspiration it is the water which acquires the predominance. 

 However, no matter what the celerity of the perspiration, there 

 is a minimum of solid components: 0.8 per cent. This remains 

 unchanged, showing that the sweat is a primitive secretion in char- 

 acter. 



Sweat contains many and different members of the series of fat 

 acids, neutral fats, alkaline sulphates and phosphates, lactic acid, and 

 urea. Horse's sweat contains albumin. 



The different strength and odor peculiar to the sweat of differ- 

 ent animals is due to the variety and abundance of the volatile fatty 

 acids. Of these, acetic, formic, and butyric prevail in general, with 

 capronic and caprillic. To their prevalence in the armpits and feet 

 is due the corresponding intensity of odor. 



It has been calculated that about 0.08 per cent, of the sweat is 

 urea. It may be increased greatly in cholera, by reason of its sup- 

 pressed passage through the kidneys. There is often observed a 

 crystalline deposit of this substance upon the surface of the body in 

 death by cholera. 



Carbonic acid and traces of nitrogen are found diffused in the 

 sweat and so eliminated from the organism. 



Perspiration is especially favored by the elevation of the body- 

 temperature ; by the wateriness of the blood ; by the energetic action 

 of the vessels of the heart ; by increase of pressure in the cutaneous 

 vessels, as during muscular exercise, etc. 



