INFLUENCE OF NERVOUS SYSTEM. 409 



chapter on NUTRITION. Its influence over secretion, as well 

 as over other functions of the body, may be excited by 

 causes acting directly upon the nervous centres, upon the 

 nerves going to the secreting organ, or upon the nerves of 

 other parts. In the latter case, a reflex action is produced : 

 thus the impression produced upon the nervous centres by 

 the contact of food in the mouth, is reflected upon the 

 nerves supplying the salivary glands, and produces, through 

 these, a more abundant secretion of saliva. 



Through the nerves, various conditions of the mind also 

 influence the secretions. Thus, the thought of food may 

 be sufficient to excite an abundant flow of saliva. And, 

 probably, it is the mental state which excites the abundant 

 secretion of urine in hysterical paroxysms, as well as the 

 perspirations and, occasionally, diarrhoea, which ensue under 

 the influence of terror, and the tears excited by sorrow or 

 excess of joy. The quality of a secretion may also be 

 affected by the mind; as in the cases in which, through 

 grief or passion, the secretion of milk is altered, and is 

 sometimes so changed as to produce irritation in the 

 alimentary canal of the child, or even death (Carpenter.) 



The secretions of some of the glands seem to bear a 

 certain relation or antagonism to each other, by which an 

 increased activity of one is usually followed by diminished 

 activity of one or more of the others; and a deranged 

 condition of one is apt to entail a disordered state in the 

 others. Such relations appear to exist among the various 

 mucous membranes : and the close relation between the 

 secretion of the kidney and that of the skin is a subject of 

 constant observation. 



