CUTANEOUS FUNCTIONS. 653 



coming from the sebaceous glands are also frequently found in it. The 

 mineral matters are composed mainly of sodium chloride, potassium 

 chloride, phosphates, and alkaline sulphates, phosphatic earths, and 

 traces of iron. The sweat, in addition, contains traces of free carbon 

 dioxide and small amounts of nitrogen. 



The following table represents the different anatyses of the sweat: 



The quantity of sweat is very variable. In man its amount has been 

 placed at five hundred to nine hundred grammes daily, although under 

 different conditions it may be increased to fifteen hundred or two thou- 

 sand grammes, or even more. Under all conditions in which the activity 

 of the skin is not absolutely prevented a considerable quantity of perspi- 

 ration is formed by the skin, the water of which evaporates as rapidly as 

 it is poured out. The secretion of sweat is then spoken of as insen- 

 sible perspiration. Under other circumstances fluid may be noticed 

 to collect on the surface of the skin, and is then spoken of as sensible 

 perspiration. The proportion of the sensible to the insensible perspi- 

 ration will depend upon a number of external conditions. Thus, sup- 

 posing the rate of secretion to remain constant, the drj-er and hotter the 

 air and the more rapid the circulation of air in contact with the body, the 

 greater will be the amount of sensible perspiration which undergoes 

 evaporation and is thus converted into insensible perspiration. On the 

 other hand, when the air is cool, and especially when saturated with 

 moisture, evaporation from the surface of the body is prevented, and, 

 even although the rate of secretion by the skin be no greater than in the 

 previous condition, the amount of sweat which remains on the surface of 

 the body as sensible perspiration will be greatly increased. 



The total amount of secretion poured out by the skin is not only 

 modified by the condition of the atmosphere, but also by the character 

 and quantit}*- of the food and by the amount of exercise, and especially 

 by the amount of fluid drunk. It is also influenced by the mental con- 

 ditions, by medicines, poisons, and, as pointed out under the heading of 



