MECHANISM OF THE SECRETION OF SWEAT. 



355 



tube in the secreting portion ; but as it passes through the epidermis, it again 

 becomes larger. It possesses the same external membrane as the glandular 

 coil and is lined generally by two layers of cells. 



In a section of the skin and the subcutaneous tissue, involving several of 

 the sudoriparous glands with their ducts, it is seen that the glandular coils 



< . I- I 1 ?-: 



generally are situated at different planes be- 

 neath the skin, as is indicated in Fig. 112. 



Sudoriparous glands in the axilla have been 

 described which do not differ so much from 

 the glands in other parts in their anatomy as 

 in the character of their secretion. The coil 

 in these glands is much larger than in other 

 parts, measuring -fa to ^ of an inch (1 to 2 

 mm.) ; the walls of the tube are thicker, and 

 they present an investment of fibrous tissue 

 with an internal layer of longitudinal, non- 

 striated muscular fibres ; and finally, the tubes 

 of the coil itself are lined with cells of epithe- 

 lium. These glands are very abundant in the 

 axilla, forming a continuous layer beneath the 

 skin. Mixed with these, are a few glands of 

 the ordinary variety. 



Estimates have been made of the number 

 of sudoriparous glands in the body and the 

 probable extent of the exhalant surface of the 



skin, but they are to be taken as merely approx- FIG. 112. sudoriparous glands ; 



nified 20 diameters (Sappey). 

 , epidermis ; 2, 2, mucous layer ; 

 3, 3, papillae ; 4, 4, derma ; 5, 5, sub- 

 cutaneous areolar tissue ; 6, 6, 6, 6, 

 sudoriparous glands ; 7, 7, adipose 

 vesicles ; 8, 8, excretory ducts in 

 the derma ; 9, 9, excretory ducts 

 divided. 



-* r j , j-ry, j_i 



imate. Krause found great differences in the 



number of perspiratory openings in different 



portions of the skin; but taking an average 



for the entire surface, it was estimated that 



the entire number of perspiratory glands is 



2,381,248 ; and assuming that each coil when unravelled measures about ^ 



of an inch (1*8 mm.), the entire length of the secreting tubes is about 2J- 



miles (3f kilometres). It must be remembered, however, that the length of 



the secreting coil only is given, and that the excretory ducts are not included. 



Mechanism of the Secretion of Sweat. The action of the skin as a glandu- 

 lar organ is continuous and not intermittent ; but under ordinary conditions, 

 the sweat is exhaled from the general surface in the form of vapor. With 

 regard to the mechanism of its separation from the blood, nothing is to be 

 said in addition to the general remarks upon the subject of secretion ; and 

 it is probable that the epithelium of the secreting coils is the active agent in 

 the selection of the peculiar matters which enter into its composition. There 

 are no examples of the separation by glandular organs of vapor from the 

 blood, and the perspiration is secreted as a liquid, which becomes vaporous 

 as it is discharged upon the surface. 



The influence of the nervous system upon the secretion of sweat is impor- 



