1 62 HUMAN PHYSIOLOGY. 



The elimination of the sweat is not intermittent, but continuous: it takes 

 place so gradually that as fast as it is formed it passes off by evaporation as 

 insensible perspiration. Under exposure to great heat and exercise the 

 evaporation is not sufficiently rapid, and it appears as sensible perspiration. 



COMPOSITION OF SWEAT. 



Water 995-573 



Urea 0.043 



Fatty matters 0.014 



Alkaline lactates o .317 



Alkaline sudorates i . 562 



Inorganic salts 2 .491 



1,000.000 



Urea is a constant ingredient. 



Carbonic acid is also exhaled from the skin, the amount being about ^o 

 of that from the lungs. 



Perspiration regulates the temperature and removes waste matters from 

 the blood; it is so important that if elimination be prevented, death occurs in 

 a short time. 



Influence of the Nerve System. The secretion of sweat is regulated 

 by the nerve system. Here, as in the secreting glands, the fluid is formed 

 from material in the lymph-spaces surrounding the gland. Two sets of 

 nerves are concerned viz., vasomotor, regulating the blood-supply; and 

 secretor, stimulating the activities of the gland cells. Generally the two 

 conditions, increased blood flow and increased glandular action, coexist. 

 At times profuse clammy perspiration occurs, with diminished blood flow. 



The dominating sweat-center is located in the medulla, though subordinate 

 centers are present in the cord. The secretory fibers reach the perspiratory 

 glands of the head and face through the cervical sympathetic; of the arms, 

 through the thoracic sympathetic, ulnar, and radial nerves; of the leg, through 

 the abdominal sympathetic and sciatic nerves. 



The sweat-center is excited to action by mental emotions, increased 

 temperature of blood circulating in the medulla and cord, increased venosity 

 of blood, many drugs, rise of external temperature, exercise, etc. 



