101 



CHAPTER VI. 



SECRETION OF THE EXTERNAL SKIN. 



Sweat. (Sudor.) 



THE sudoriparous glands continuously secrete a very consi- 

 derable amount of watery fluid, which, in consequence of the ex- 

 tent of surface over which these glands are distributed, usually 

 passes off directly in the shape of vapour, leaving behind, how- 

 ever, on the skin, its various solid constituents, mixed with the 

 secretion of the sebaceous glands. It is only under the influ- 

 ence of active exercise, high external temperature, or certain 

 forms of disease, that the secretion is elaborated in such quan- 

 tity as to stand in drops on the skin, instead of being carried 

 off as insensible vapour ; it is then termed sweat. 



Attempts have been made by Sanctorius, Dodart and Reil, 

 and more recently by Lavoisier and Seguin, to determine the 

 quantity of fluid which escapes from the skin within a certain 

 time, in the form of vapour. Seguin found that, on an average, 

 18 grains of fluid were discharged in a minute by the skin 

 and lungs ; the former exhaling 11 and the latter 7 grains. The 

 minimum exhalation from both sources amounted to 11 grains; 

 the maximum, in a state of rest, to 32 grains in a minute. 

 From these data the maximum of matter lost by the body 

 through the skin and lungs in 24 hours, would amount to 5 

 pounds, and the minimum to 1 pound, 11 ounces, and 4 drachms. 

 Taking the average of 11 grains in the minute, the whole quan- 

 tity would amount to 29 ounces of fluid. 



The amount of solid constituents carried off with the fluid, 

 is comparatively very small, and does not exceed 7 or 8 scruples 

 in the 24 hours : all the rest is mere water, with some carbonic 

 acid, and perhaps some nitrogen. 



The solid constituents of the sweat consist of a mixture of 

 salts and extractive matters, of which the latter preponderate ; 

 the principal ingredient of the salts is chloride of sodium. 



