EXCRETION 



The sweat* is a colorless, slightly turbid fluid, alkaline, neutral or acid in 

 reaction, of a saltish taste, and peculiar characteristic odor. 



Of the several substances it contains, however, only the carbonic acid and 

 water need particular consideration. 



The quantity of watery vapor excreted from the skin is, on an average, 

 between 750 and 1,000 cubic centimeters daily. This subject has been very 

 carefully investigated by La cisier and Sequin. The latter chemist enclosed 

 his body in an air-tight bag provided with a mouthpiece. The bag was 

 closed by a strong band above, and the mouthpiece adjusted and gummed 

 to the skin around the mouth. He was weighed, then remained quiet for 

 several hours, after which time he was again weighed. The difference in 

 the two weights indicated the amount of loss by pulmonary exhalation. 

 Having taken off the air-tight dress, he was immediately weighed again, and 

 a fourth time after a certain interval. The difference between the two weights 

 last ascertained gave the amount of the cutaneous and pulmonary exhalation 

 together; by subtracting from this the loss by pulmonary exhalation alone, 

 while he was in the air-tight dress, he ascertained the amount of cutaneous 

 transpiration. The average loss by cutaneous and pulmonary exhalation in 

 a minute during a state of rest is eighteen grains, the minimum eleven grains, 

 the maximum thirty-two grains. Of the eighteen grains, eleven pass off by 

 the skin and seven by the lungs. 



The quantity of watery vapor lost by transpiration is of course influenced 

 by all external circumstances which affect the exhalation from evaporating 

 surfaces, such as the temperature, the hygrometric state, and the stillness 

 of the atmosphere. But, of the variations to which it is subject under the 

 influence of these conditions, no calculation has been exactly made. 



The quantity of carbonic acid exhaled by the skin on an average is said to 

 be about one-two-hundredth of that eliminated by the pulmonary respiration. 



The cutaneous exhalation is most abundant in the lower classes of ani- 

 mals, more particularly the naked amphibia, as frogs and toads, whose skin 

 is thin and moist, and readily permits an interchange of gases between the 

 blood circulating in it, and the surrounding atmosphere. Bischoff found that, 

 after the lungs of frogs had been tied and cut out, from 3 to 4 c.c. of car- 

 bonic-acid gas was exhaled by the skin in eight hours. And this quantity 

 is very large, when it is remembered that a full-sized frog will generate only 

 about 10 c.c. of carbonic acid by his lungs and skin together in six hours. 



The importance of the respiratory function of the skin, which was once 

 thought to be proved by the speedy death of animals whose skins, after re- 

 moval of the hair, were covered with an impermeable varnish, has been shown 

 by further observations to have no foundation in fact. The immediate cause 

 of death in such cases is the loss of temperature. A varnished animal is 

 said to have suffered no harm when surrounded by cotton padding, and to 

 have died when the padding was removed. 



