43 6 THE SKIN. 



glands"; for not more than about 3,365 grains could be 

 evaporated from such a surface in twenty-four hours, 

 under the ordinary circumstances in which the surface of 

 the skin is placed. This estimate is not an improbable 

 one, for it agrees very closely with that of Milne-Edwards, 

 who calculated that when the temperature of the atmo- 

 sphere is not above 68 F., the glandular secretion of the 

 skin contributes only ith to the total sum of cutaneous 

 exhalation. 



The quantity of watery vapour lost by transpiration, is 

 of course influenced by all external circumstances which 

 affect the exhalation from other 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 calcula- 

 tion has been exactly made. 



Neither, until recently, has there been any estimate of 

 the quantity of carbonic acid exhaled by the skin on an 

 average, or in various circumstances. Regnault and Reiset 

 attempted to supply this defect, and concluded, from some 

 careful experiments, that the quantity of carbonic acid 

 exhaled from the skin of a warm-blooded animal is about 

 -Vth of that furnished by the pulmonary respiration. Dr. 

 Edward Smith's calculation is somewhat less than this. 

 The cutaneous exhalation is most abundant in the lower 

 classes of animals, more particularly the naked Am* 

 phibia, 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, about a quarter of a cubic inch of carbonic 

 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 half a cubic inch of 

 carbonic acid by his lungs and skin together in six hours 

 (Milne-Edwards and Miiller). That the respiratory func- 



