388 MANUAL OF PHYSIOLOGY. 



rate them. There can be no doubt, however, that a special ner- 

 vous control is exerted over the production of sweat. This ap- 

 pears to be observable in some diseases, the poisons of which 

 variously affect the two sets of nerves. Thus, in fever, we ob- 

 serve a dry, red skin accompanied by an 1 increased supply of 

 blood, and a suppression of the secretion of the sweat glands ; 

 while in certain stages of acute rheumatism, the exact opposite 

 is seen, i. e., a profuse sweat drips from the pale, bloodless skin. 

 It has, moreover, been recently shown that in some animals (cats) 

 the stimulation of the sciatic nerve, causing contraction of the 

 blood vessels, produces at the same time a copious secretion of 

 sweat ; and a warm atmosphere is said to have no effect on the 

 secretion of a limb the nerve of which has been cut, although 

 the warmth be so great as to make the rest of the animal's body 

 sweat profusely. 



The effect of drugs upon the cutaneous secretion is well known. 

 There is a large group of medicines, especially pilocarpin, which 

 produce an increased flow, while many others, notably atropin, 

 have a contrary effect. 



CUTANEOUS DESQUAMATION. 



Together with cutaneous excretion should be mentioned the 

 continuous and extensive loss all over the surface of the body 

 from the casting off of the superficial layers of the dried horny 

 cells of which the outer part of the skin is composed. 



The way in which the cells of the mammary gland produce 

 their important secretion is by their protoplasm adopting a pecu- 

 liar method of fat manufacture, while all the strength of its 

 nutritive powers is devoted to the elaboration of the constituents 

 of milk. In a similar way the cells of the epidermis devote their 

 nutritive activity to the production of a certain material keratin, 

 which cannot be called a secretion in the ordinary acceptation of 

 the term, but which is certainly elaborated as the result of the 

 nutritive changes going on in the protoplasm of the cell during 

 its life history, just as we know that many other substances are 

 produced as the result of the working of gland cells. 



The work of the epidermal cells supplies not a peculiar 



