THE SKIN AND ITS APPENDAGES. 417 



sensations and emotions, by stimulation of the sciatic nerve, follow- 

 ing the administration of pilocarpin, etc. 



Ordinarily the secretion of sweat is scarcely noticeable, as the 

 droplets evaporate almost as rapidly as they appear on the sur- 

 face of the skin. But even so, from 700 to 900 c.c. of water are 

 daily eliminated by the body. Artificially this amount can be 

 greatly increased, and it is stated that from 6000 to 8000 c.c. may 

 be excreted in the twenty-four hours if the body is kept at a tem- 

 perature of from 40 to 50 C., and large amounts of fluid are 

 ingested. 



Sweat, recently secreted, is more or less turbid, owing to an admix- 

 ture of desquamated epithelial cells, and droplets of fat, which 

 are in part derived from the sebaceous glands, but are to some 

 extent also referable to the sweat-glands proper. After filtration it 

 appears as a clear, transparent, colorless fluid, of a salty, somewhat 

 acrid taste, and a very characteristic odor, which differs somewhat 

 according to the region of the body from which the sweat is derived. 

 Its specific gravity varies between 1.004 and 1.005. 



At the beginning of its secretion the sweat presents an acid reac- 

 tion, which is probably referable to an admixture of fatty acids 

 derived from the sebaceous glands ; later, however, it is alkaline. 



Under normal conditions the sweat is essentially a very dilute 

 aqueous solution of mineral salts, but in addition we also find small 

 amounts of many urinary components, such as urea, uric acid, 

 kreatinin, aromatic oxy-acids, volatile fatty acids, skatoxyl and 

 phenol sulphate, besides fat, cholesterin, traces of albumin, salts of 

 lactic acid, and so-called sudoric or hydratic acid, etc. Larger 

 amounts of solids are principally met with in cases of renal insuffi- 

 ciency, and it may then happen that the elimination of urea through 

 the sweat increases to 10 grammes, as compared with 0.0431.55 

 pro mille, which may be regarded as normal. In some cases of 

 this kind the urea may actually be found in the form of a fine cry- 

 stalline powder deposited all over the skin. Glucose has been 

 observed in diabetes. Cystin has been noted in cases of cystinuria, 

 and abnormally large amounts of uric acid have been found in 

 gout. In jaundice bilirubin may color the sweat a bright yellow. 

 A blue and red color, which is thought to be referable to the 

 presence of indigo-blue and indigo-red, has also been observed 

 (chromhidrosis or cyanhidrosis) ; and it is stated that in rare 

 instances blood may appear in the sweat (haBmahidrosis). It is 

 noteworthy, furthermore, that a number of foreign substances, 

 when ingested by the mouth, such as quinin, the various salts 

 of iodine, mercury, and arsenic, are in part eliminated in the 

 sweat. 



A general idea of the quantitative composition of the sweat may 

 be formed from the accompanying analyses, which are taken from 

 Favre, Schottin, and Funke. 



27 



