OP PERSPIRATION. 239 



exhalation. Then, taking off the air-tight bag, he was weighed again, 

 and after another interval once more. The difference between the two 

 last weighings is the amount of the pulmonary and cutaneous exhalation 

 together, and from these data, by a simple arithmetical calculation, the 

 value of each may be determined. By these experiments it appeared 

 that the loss by pulmonary and cutaneous exhalation together is, on an 

 average, eighteen grains per minute, of which seven issue from the lungs 

 and eleven from the skin. The variable action of the skin is, however, 

 well illustrated by the extreme numbers observed, the minimum being 

 eleven grains, and the maximum thirty-two. From the experiments of 

 Valentin, the average of loss through the skin is two pounds and nearly 

 half an ounce a day. Seguin's experiments would make it two pounds 

 and three quarters. It has been shown in Chapter X. that Causesofthe 

 the action of the skin is partly meteorological : the amount variable action 

 of water passing through it depends on the dew-point, the 

 atmospheric temperature, the conductibility and perviousness of the cloth- 

 ing. Whatever physical circumstances promote surface evaporation cor- 

 respondingly promote the action of the skin. Moreover, this membrane 

 acts vicariously with the kidneys, and this not only as regards the water, 

 but also as regards the solid matter, a large amount of which is thrown 

 off in the course of the day. 



In all computations of the quantity of water eliminated by the skin, 

 it should not be overlooked that any inclosing barrier or bag must neces- 

 sarily occasion a complete alteration in the conditions under which the 

 action is occurring. On the whole, it is perhaps most probable that the 

 ratio of the matters expired through the skin and those expired by the 

 lungs is as 9 to 5. 



Besides the water secreted by the sudoriparous glands, carbonic acid 

 and nitrogen escape. Their relative proportion is variable, Transpiration 

 and seems to depend, among other things, upon the nature of of gases. 

 the food, the carbonic acid increasing under a vegetable, and the nitrogen 

 under an animal diet. From the experiments of Dr. J. C. Draper, above 

 referred to, it appears that the absolute amount of these gases is influ- 

 enced by exercise. 



OF PERSPIRATION. When the atmospheric temperature is high, and 

 more particularly if muscular exertion be resorted to, the ingredients of 

 quantity of water issuing from the perspiratory ducts is so perspiration, 

 great that it can not be evaporated. It then exudes as drops of sweat, 

 which become mingled with the oily secretion prepared by the sebaceous 

 glands. From this commingling it is scarcely possible to obtain the 

 sweat, in an uncontaminated condition, suitable for analysis, or even to 

 exclude the detritus of the cuticle itself. In a thousand parts of sweat 

 there are from five to twelve and a half parts of solid material. Thenard, 



