90 HUMAN PHYSIOLOGY. 



birth consists of the residue of the sebaceous matters, containing epithelial 

 cells and fatty matters; it seems to keep the skin soft and supple, and 

 guards it from the effects of the long-continued action of water. 



The Sudoriparous Glands excrete the sweat ; they consist of a mass 

 or coil of a tubular gland duct, situated in the derma and in the subcuta- 

 neous tissue ; average the 7 ^ of an inch in diameter, and are surrounded by 

 a rich plexus of capillary blood vessels. From this coil the duct passes in a 

 straight direction up through the skin to the epidermis, where it makes a 

 few spiral turns and opens obliquely upon the surface. The sweat glands 

 consist of a delicate homogeneous membrane lined by epithelial cells, 

 whose function is to extract from the blood the elements existing in the 

 perspiration. 



The glands are very abundant all over the cutaneous surface, as many as 

 3528 to the square inch, according to Erasmus Wilson. 



The Perspiration is an excrementitious fluid, clear, colorless, almost 

 odorless, slightly acid in reaction, with a specific gravity of 1.003 or I - OO 4- 



The total quantity of perspiration excreted daily has been estimated at 

 about two pounds, though the amount varies with the nature of the food 

 and drink, exercise, external temperature, season, etc. 



The elimination of the sweat is not intermittent, but continuous ; but it 

 takes place so gradually that as fast as it is formed it passes off by evapora- 

 tion as insensible perspiration. Under exposure to great heat and exercise 

 the evaporation is not sufficiently rapid, and it appears as sensible perspira- 

 tion. 



COMPOSITION OF SWEAT. 



Water, 995-573 



Urea, . 0.043 



Fatty matters, 0.014 



Alkaline lactates, 0.317 



Alkaline sudorates, 1.562 



Inorganic salts, 2.491 



1000.00 



Urea is a constant ingredient. 



Carbonic acid is also exhaled from the skin, the amount being about ^ 

 of that from the lungs. 



Perspiration regulates the temperature, and removes waste matters from 

 the blood ; it is so important, that if elimination be prevented death occurs 

 in a short time. 



Influence of the Nervous System. The secretion of sweat is regu- 

 lated by the nervous system. Here, as in the secreting glands, the fluid is 



