PERSPERATIOX. 137 



the probable extent of the exhalant surface of the skin. 

 One of the most careful, and probably the most reliable 

 of these estimates, is that made by Krause ; but like all 

 estimates of this kind, the results are to be taken as merely 

 approximative. Krause found great differences in the num- 

 ber of perspiratory openings in different portions of the skin, 

 and estimated the number in a square inch in certain ,parts, 

 as follows : On the forehead, he found 1,258 glands to a 

 square inch ; on the cheeks, 548 ; on the anterior and lateral 

 portions of the neck, 1,303 ; on the breast and abdomen, 

 1,136 ; on the back of the neck, the back, and the nates, 417; 

 the forearm, inner surface, 1,123, and the outer surface, 1,093 ; 

 on the hand, palmar surface, 2,736, and dorsal surface, 1,490 ; 

 on the upper part of the thigh, inner surface, 576, outer sur- 

 face, 554 ; on the lower part of the thigh, inner surface, 576 ; 

 on the foot, plantar surface, 2,685, and the dorsal surface, 

 924. 1 From these figures it is estimated that the entire 

 number of perspiratory glands is 2,381,248 ; and assuming 

 that each coil when unravelled measures about ^ of an inch, 

 the entire length of the secreting tubes is about 2J miles. 

 It must be remembered, however, that the length of the 

 secreting coil only is given, and that the excretory ducts are 

 not included. 8 



Mechanism of the Secretion of Sweat. The action of the 

 skin as a glandular organ is continuous and not intermit- 

 tent ; but under ordinary conditions, the sweat is exhaled 

 from the general surface in the form of vapor. With regard 



1 KRAUSE, Article, Haut. WAGNER'S Handworterbuch der Physiologic, 

 Braunschweig, 1844, Bd. ii., S. 131. 



2 If the above calculation be approximative^ correct, the estimate given 

 by Wilson, which is frequently quoted in works on physiology, must be very 

 much exaggerated. Wilson assumes that the average number of pores to the 

 square inch of surface is 2,800 ; and including the length of excretory duct, 

 he estimates that each tube measures about a quarter of an inch. Assuming 

 that the number of square inches of surface is 2,500 (a little more than the esti- 

 mate of Haller, which is fifteen square feet) it is estimated that the total length 



