INFLUENCE OF THE NERVOUS SYSTEM ON SECRETION 32! 



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 sen- 

 sory nerves by the contact of food in the mouth leads to afferent nerve im- 

 pulses to the secretory center in the central nervous system which is reflected 

 by the nerves supplying the salivary glands, and produces, through these, a 

 more abundant secretion of the saliva. 



Through the nerves, various conditions of the brain also influence the 

 secretions. Thus, the thought of food may be sufficient to excite an abun- 

 dant flow of saliva. And, probably, it is the mental state which excites the 

 abundant secretion of urine in hysterical paroxysms, as well as the perspira- 

 tions, and occasionally diarrhea, 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 mental conditions, 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. 



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