DESQUAMATION. 385 



of pigments, varying in color from brick-red to bluish-black, 

 which need not be here further described. 



The effect of nervous influence on the secretion of sweat is so as- 

 sociated with the nervous mechanisms of the cutaneous vessels 

 that, under ordinary circumstances, it is a difficult matter to sep- 

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

 vous control is exerted over the production of sweat. This appears 

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

 affect the two sets of nerves. Thus, in fever, we observe a dry 

 red skin accompanied by an increased supply of blood, and a sup- 

 pression of the secretion of the sweat glands ; whilst in certain 

 stages of acute rheumatism, the exact opposite is seen, i.e., a pro- 

 fuse 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 bloodvessels, pro- 

 duces 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 con- 

 tinuous 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, whilst all the strength of its nu- 

 tritive 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 



