APPENDAGES OF THE SKIN. 91 



formed from material in the lymph spaces surrounding the gland. Two 

 sets of nerves are concerned, viz : vasomoior, regulating the blood supply ; 

 and secretory, 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 centre is located in the medulla, though subordi- 

 nate centres are present in the cord. The secretory fibres reach the perspi- 

 ratory 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 centre is excited to action by mental emotions, increased tem- 

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

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



