PERSPIRATION. 281 



which perspire copiously, the loss by evaporation at 68 is thus 

 found six times greater than by mere secretion, and the propor- 

 tion in man, the temperature being the same and the air dry, must 

 be greater, as his skin secretes much less. 



The secreted fluid may be carried off by evaporation as quickly 

 as it is formed, so as to be insensible perspiration ; or may be too 

 abundant for this, and appear as sweat. The transuded fluid may 

 also be condensed and precipitated on the skin in the form of 

 sweat. 



The cutaneous secretion is not so much augmented by moderate 

 elevations of temperature as might be imagined ; but, as the 

 elevation proceeds, the augmentation of secretion becomes more 

 than proportionate. It appeared increased after meals and during 

 sleep, and, though subject to great fluctuations, if observed at 

 short intervals, from accidental changes in the atmosphere, under- 

 went successive diminutions when observed every six hours, from 

 six o'clock A. M. the hour of rising till the return of the 

 same period. In frogs this regular diminution might be detected 

 every three hours. r 



In frogs the cutaneous secretion continues, though at its mini- 

 mum, in the moistest air and in water; and it would appear to do 

 so also in man. 8 



The matter of the cutaneous secretion contains an acid, pro- 

 bably the acetic, chloride of potassium and sodium, acetate of 

 soda, and perhaps albumen. 1 What evaporates is mere water. 



Dr. Edwards makes some curious remarks upon the different 

 effects of dry and moist air, when hot, and when cold. When 

 hot, dry air will of course communicate less heat to the body 

 than if moist, and will, by its dryness, cause more evaporation ; 

 and thus carry off more heat ; so that the two operations of air, 

 dry or moist, will correspond in temperatures above that of the 

 body. When cold, dry air will remove less heat from the body 

 than moist ; but, by its dryness, will cause more evaporation, and 

 therefore tend to cool more, so that the two operations oppose 

 each other in temperatures inferior to that of the body. u The 

 same remarks apply to cold water. 



r For what relates to this function in the batrachians, see 1. c. part i. c. v. 

 and vi. 



s p. 92. sqq. 98. sqq. 351. sqq. 



1 Berzelius, Ardmcd Chemistry, p. 95. 



u 1. c. p. 386. sq. 



