868 PHYSIOLOGY OF DIGESTION AND SECRETION. 



less compact knot, thus increasing the extent of the secreting sur- 

 face. The larger ducts have a thin, muscular coat of involuntary 

 tissue that may possibly be concerned in the ejection of the secre- 

 tion. The secretory cells in the terminal portion are columnar in 

 shape, possess a granular cytoplasm, and are arranged in a single 

 layer. The amount of secretion formed by these glands varies 

 greatly, being influenced by the condition of the atmosphere as re- 

 gards temperature and moisture, as well as by various physical and 

 psychical states, such as exercise and emotions. The average quan- 

 tity for twenty-four hours is said to vary between 700 and 900 gms., 

 although this amount may be doubled under certain conditions. 



According to an interesting paper by Schierbeck,* the average 

 quantity of sweat in twenty-four hours may amount to 2 to 3 liters 

 in a person clothed, and therefore with an average temperature 

 of 32 C. surrounding the skin. This author states that the amount 

 of sweat given off from the skin in the form of insensible perspira- 

 tion increases proportionately with the temperature until a certain 

 critical point is reached (about 33 C. in the person investigated) , 

 when there is a marked increase in the water eliminated, the in- 

 crease being simultaneous with the formation of visible sweat. At 

 the same time there is a sudden increase in the C0 2 eliminated from 

 the skin. It is possible that the sudden increase in CO 2 is an in- 

 dication of greater metabolism in the sweat glands in connection 

 with the formation of visible sweat. 



Composition of the Secretion. The precise chemical composition 

 of sweat is. difficult to determine, owing to the fact that as usually 

 obtained it is liable to be mixed with the sebaceous secretion. Nor- 

 mally it is a very thin secretion of low specific gravity (1.004) and 

 an alkaline reaction, although when first secreted the reaction may 

 be acid owing to admixture with the sebaceous material. The 

 larger part of the inorganic salts consists of sodium chlorid. Small 

 quantities of the alkaline sulphates and phosphates are also pres- 

 ent. The organic constituents, though present in mere traces, are 

 quite varied in number. Urea, uric acid, creatinin, aromatic oxy- 

 acids, ethereal sulphates of phenol and skatol, serin (oxyaminopro- 

 pionic acid), and albumin, are said to occur when the sweating is 

 profuse. Argutinsky has shown that after the action of vapor 

 baths, and as the result of muscular work, the amount of urea 

 eliminated in this secretion may be considerable. Under patho- 

 logical conditions involving a diminished elimination of urea through 

 the kidneys it has been observed that the amount found in the 

 sweat is markedly increased, so that crystals of it may be deposited 

 upon the skin. Under perfectly normal conditions, however, it 



*"Archiv f. Physiologic," 1893, 116; see also Willebrand, "Skandi- 

 navisehes Archiv f. Physiologic," 13, 337, 1902. 



