SECRETION OF SWEAT 213 



This occurs during violent exercise, e. g. However, that 

 the production of sweat is not altogether dependent on this 

 factor is shown by profound sweating in shock, nausea and 

 like conditions when the skin is pale and cold, and by dry- 

 ness of the flushed skin in febrile diseases. Furthermore, 

 experiments on inferior animals have revealed fibers which 

 influence the secretion of sweat without affecting the blood 

 flow. 



Practically, in health, the only conditions which increase 

 the flow of perspiration are muscular exercise and a high ex- 

 ternal temperature. Of these, exercise probably works 

 through the nerve centers; external heat does not stimulate 

 the glands directly, but irritates the cutaneous terminations 

 of afferent fibers which convey impressions to the sweat cen- 

 ters, whence messages are sent out by secretory (fibers to the 

 glandular epithelium and their activity begins. In both cases 

 ihere is accompanying dilatation of the superficial vessels 

 under the influence of the vaso-dilator fibers. 



It is supposed that the chief center is in the medulla ob- 

 longata and that secondary centers exist in the lumbar re- 

 gion of the cord. 



The amount of CO2 eliminated by the skin is inconsider- 

 able in the human being. 



