CUTANEOUS SYSTEM OR SKIN. 19] 



great variations in the amount of fluid eliminated by the sudori- 

 parous glands, which are governed by the temperature of the skin ; 

 and partly because the secretion can scarcely be collected for 

 analysis, free from the sebaceous and other matters which accumu- 

 late on the surface of the skin. According to Anselmino it varies 

 from J to 1 J per cent. ; and consists in part of lactic acid, to which 

 the acid reaction and sour smell of the secretion are due ; in part 

 of a proteine compound, which is probably furnished by the epithe- 

 lium cells that line the tubes ; and in part of saline matters, directly 

 proceeding from the serum of the blood. Sanctorius proved that 

 three-fourths of all taken into the system passed off by the skin. 



The amount of fluid excreted from the skin is almost entirely 

 dependent upon the temperature of the surrounding medium ; being 

 increased with its rise, and diminished with its fall. The object of 

 this variation is very evident ; being the regulation of the tempera- 

 ture of the body. When the surface is exposed to a high degree 

 of external heat, the increased amount of fluid set free from the 

 perspiratory glands becomes the means , of keeping down its own 

 temperature ; for this fluid is then carried off in a state of vapor, 

 as fast as it is set free ; and in its change of form, it withdraws a 

 large quantity of caloric from the surface. But if the hot atmo- 

 sphere be already loaded with vapor, this cooling power cannot be 

 exerted ; the temperature of the body is raised, and death super- 

 venes, if the experiment be long continued. The cause of the 

 increased secretion is probably to be looked for in the increased 

 determination of blood to the skin, which takes place under the 

 stimulus of heat. The entire loss by exhalation from the lungs and 

 skin, during the twenty-four hours, seems to average a little above 

 two pounds. In a warm dry atmosphere, however, it has been 

 found to rise to as much as five pounds ; whilst in a cold damp one, 

 it may be lowered to one and two-thirds of a pound. Of this 

 quantity, the pulmonary exhalation is usually somewhat less than 

 one-third, and the cutaneous somewhat more than two-thirds ; but 

 when the quantity of fluid lost is unusually great the increase must 

 be chiefly in the cutaneous exhalation ; since the amount of exhala- 

 tion from the lungs is not influenced by the external temperature, 

 but only by the degree in which the surrounding air is previously 

 saturated with moisture. 



The variations in the amount of fluid set free by cutaneous and 

 pulmonary exhalation, are counterbalanced by the regulating action 

 of the kidney ; which allows a larger proportion of water to be 



