280 THE INTERNAL SECRETIONS 1920 



terdependent ; all act in a somewhat different manner, 

 yet a balance normally exists between them. All are 

 undoubtedly supplied with a double innervation from 

 the involuntary nervous system. Stimulation of one 

 member of the group automatically results in stimula- 

 tion of the others. The thyroid, being most sensitive, 

 responds most easily to vasodilating stimuli, and read- 

 ily increases its secretion. Were it checked merely by a 

 cessation of vasodilating stimuli or the registration of a 

 superior vasoconstricting stimulus, it might pour too 

 much secretion into the blood stream and sustain vaso- 

 dilation to dangerous lengths. An excess of thyroid 

 secretion in the blood stream, however, destroys the 

 normal interglandular balance, and stimulates the an- 

 tagonistic adrenal medulla and posterior pituitary to 

 increase action. Hyperactivity of these glands in turn 

 automatically inhibits thyroid activity, and their secre- 

 tions thrown into the blood stream neutralize or inhibit 

 the physiological action of the excess thyroid content 

 therein, tend to overcome vasodilation, and reenforce 

 vasoconstriction. 



Such would appear to be the logical mechanism of 

 normal vasomotor control in the healthy individual. 

 Normally there exists a perfect response of the glands 

 of internal secretion to involuntary nervous stimuli, 

 and a perfect balance of activity between such glands 

 themselves. This normal response may be altered and 

 the balance impaired, however, by continuous stimula- 

 tion, by overexertion, by pronounced physical or men- 

 tal fatigue, by disease, including focal infection, by se- 

 vere nervous shock, or by the entrance into the circula- 

 tory system of foreign protein matter. Rogers (7) 

 suggests that the end-plates of the involuntary nerves 

 are affected by fatigue, just as are those of the volun- 

 tary system. As a voluntary nerve trunk may be irri- 

 tated by repeated electric shocks until its functionation 

 ceases because of fatigue, so presumably may the more 



