536 INFLUENCES AFFECTING THE SECRETION OF SWEAT. 



INFLUENCES AFFECTING THE SECRETION OF SWEAT. 



The secretion of the skin, which on the average equals about -g^ of the 

 weight of the body, or twice the elimination through the lungs, may 

 be increased or diminished as a result of various influences. The tendency 

 to sweating varies greatly in different individuals. Among the influences 

 affecting the secretion of sweat the following are known : i . Elevation 

 of the surrounding temperature causes marked redness of the skin and 

 profuse secretion of sweat. Cold and a temperature of the skin above 

 50 C. suppress the secretion. 2. The presence of an increased amount 

 of water in the blood, principally after the ingestion of warm fluid in 

 large amount, increases the sweat. 3. Marked activity on the part of 

 the heart and the vessels, in consequence of which the blood-pressure in 

 the capillaries of the skin is increased, has a similar effect. In this 

 category belongs, also, the increased sweating in consequence of violent 

 muscular activity. Under such circumstances the excretion of nitro- 

 gen through the sweat is increased. 4. Certain agents hydrotics 

 increase sweating, such as pilocarpin, physostigma, strychnin, picro- 

 toxin, muscarin, nicotin, camphor, and ammonium-combinations. 

 Others, such as atropin and morphin in large doses, diminish the 

 sweat. 5. The antagonism that exists between the secretion of sweat 

 and the secretion of urine and the intestinal discharges, probably in 

 consequence principally of mechanical influences, is especially note- 

 worthy in so far as abundant micturition, as, for -instance, in cases of 

 diabetes, and thin stools are associated with dryness of the skin. 



If the amount of sweat is increased, the proportion of salts, urea and 

 albumin present increases; while the remaining organic substances 

 diminish. The more saturated the air with watery vapor, the more 

 readily does the secretion appear in drops upon the surface; while in 

 dry air in active motion the secretion appears as fluid later in conse- 

 quence of the rapid evaporation. 



NERVOUS CONTROL AFFECTING THE SECRETION OF SWEAT. 



As in the secretion of saliva, vascular nerves are principally active 

 in the secretion of sweat, in addition to the true secretory nerves; and 

 most frequently the vasodilators, as indicated by the sweating when the 

 skin is reddened. The observation of sweating when the skin is pale 

 (the sweating of fear and of death) shows, however, that also in the 

 presence of vasoconstriction, the sweat -fibers may at the same time 

 be active. 



Under certain conditions an increase in the amount of blood present appears 

 alone to be sufficient for the occurrence of sweating. In favor of this view is the 

 observation of Dupuy, who noted unilateral sweating of the neck in a horse 

 after division of the cervical sympathetic; and in opposition to this view is the 

 statement of Nitzelnadel, who observed diminution of sweating in human beings 

 after percutaneous galvanization of the cervical sympathetic. 



Independently of the circulation, sweat -nerves of independent activ- 

 ity control the secretion from the surface of the body. Irritation of the 

 appropriate nerve-trunk still causes transitory secretion of sweat even if 

 the extremity has been previously amputated ; and therefore the circula- 

 tion no longer exists. In addition, the secretion of sweat may take place 

 under higher pressure than that of the blood. In the healthy body, pro- 



