488 PHYSIOLOGY CHAP. 



phases of a single secretory process. It cannot be absolutely denied 

 that a minimal degree of aqueous evaporation may take place over 

 the entire surface of the skin independent of any process of secre- 

 tion, but there can be no doubt that almost the whole of the 

 insensible loss of water suffered by the skin is due to the secretion 

 of sweat, which evaporates as fast as it creeps from the orifices of 

 the glands. Evidence for this has recently been given by Aubert 

 in his photographs of the sweat-drops during insensible perspiration 

 (Fig. 136). 



It is also important to note from recent work on general 

 metabolism (that of Pettenkofer and Voit in particular) on 

 calculating the average results obtained by the evaporation of 



FIG. 136. Sweat prints from back of hand. (Aubert.) The pores or mouths of the sweat 

 glands are shown as white dots on a black ground. 



water in cutaneous and pulmonary respiration jointly, as compared 

 with the water eliminated in the urine, that 



the dog excretes 70 % H 9 in the urine, 30 % in cutaneous secretion. 

 man 60 % 40 % 



horse 30% 70% 



In carnivora, therefore, the loss of water by the kidneys 

 greatly exceeds that by sweating; in herbivora, the contrary is 

 the case ; in man, excretion by the kidneys is slightly in excess of 

 that by the sudoriferous glands, approximating to the carnivora 

 rather than to the herbivora. The daily loss of water by the 

 skin amounts in man on an average to 6J the body- weight, and 

 is almost double that by pulmonary excretion. 



As every one knows, there is a marked antagonism between 

 the loss of water by the kidneys and intestines, and that given off 



