346 THE SKIN. 



thirty-two grains ; and that of the eighteen grains, eleven pass 

 off by the ski a, and seven by the lungs. The maximum loss 

 by exhalation, cutaneous and pulmonary, in twenty-four hours, 

 is about 3f lb.; the minimum about H lb. Valentin found 

 the whole quantity lost by exhalation from the cutaneous and 

 respiratory surfaces of a healthy man who consumed daily 

 40,000 grains of food and drink, to be 19,000 grains or 2f lb. 

 Subtracting from this, for the pulmonary exhalation, 5000 

 grains, and, for the excess of the weight of the exhaled car- 

 bonic acid over that of the equal volume of the inspired oxy- 

 gen, 2256 grains, the remainder, 11,744 grains, or nearly if 

 lb., may represent an average amount of cutaneous exhalation 

 in the day. 



The large quantity of watery vapor thus exhaled from the 

 skin, will prove that the amount excreted by simple transuda- 

 tion through the cuticle must be very large, if we may take 

 Krause's estimate of about eight square inches for the total 

 evaporating surface of the sudoriparous glands ; for not more 

 than about 3365 grains could be evaporated from such a sur- 

 face 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 atmosphere is not above 68 F., the glandular secretion 

 of the skin contributes only Jth to the total sum of cutaneous 

 exhalation. 



The quantity of watery vapor lost by transpiration, is of 

 course influenced by all external circumstances which affect 

 the exhalation irom 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 un- 

 der the influence of these conditions, no calculation 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 exper- 

 iments, that the quantity of carbonic acid exhaled from the 

 skin of a warm-blooded animal is about -^th of that furnished 

 by the pulmonary respiration. Dr. Edward Smith's calcula- 

 tion is somewhat less than this. The cutaneous exhalation is 

 most abundant in the lower classes of animals, more particu- 

 larly 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 atmos- 

 phere. Bischoff found that, after the lungs of frogs had been 



