SKIN. 179 



taining 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 the amniotic 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 

 subcutaneous tissue, average ^ 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 homo- 

 geneous 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 1003 to 

 1004. 



The total quantity of perspiration excreted daily has been esti- 

 mated 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 ; 

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

 by evaporation as insensible perspiration. Under exposure to great 

 heat and exercise the evaporation is not sufficiently r.apid, and it 

 appears as sensible perspiration. 



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 



1,000.000 



Urea is a constant ingredient. 



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

 about Z^Q of that from the lungs. 



Perspiration regulates the temperature and removes waste matters 



