24: SECRETION. 



The theory that the discharge of the secretions is due 

 simply to mechanical causes, and is attributable solely to the 

 increase in the pressure of blood, cannot be sustained. 

 Pressure undoubtedly has considerable influence upon the 

 activity of secretion ; but the flow will not always take place 

 in obedience to simple pressure, and secretion may be in- 

 duced for a limited time without any increase in the quan- 

 tity of blood circulating in the gland. In the numerous ex- 

 periments by Bernard upon the influence of the circulation 

 upon secretion in the submaxillary gland of the dog, these 

 facts are very clearly shown. By very powerful galvaniza- 

 tion of what he termed the motor nerve of the gland (the 

 chorda tympani), secretion was excited, but the circulation 

 was reduced ; and again, after ligation of the vein, by which 

 the gland was engorged with blood and the circulation could 

 not be modified, galvanization of the nerve was nevertheless 

 followed by an increase in the secretion. A slight secretion 

 was also produced by galvanization of the nerve after the 

 artery supplying the gland had been tied. These experi- 

 ments are made with great facility upon the submaxillary 

 gland of the dog, for the reason that the parts may be ex- 

 posed and operated upon without interrupting the secretory 

 function, and the nerves and vessels communicating with the 

 gland can be easily isolated. The function of most of the 

 glands, however, becomes so much disturbed by exposure, 

 that the influence of the nerves upon their action is observed 

 with great difficulty. 



From the experiments just cited, Bernard concludes that 

 the glands possess a peculiar irritability, which is manifested 

 by their action in response to proper stimulation. During 

 their secretion, they generally receive an increased quantity 

 of blood ; but this is not indispensable, and secretion may be 

 excited without any modification of the circulation. This 

 irritability will disappear when the artery supplying the part 

 with blood is ligated for a number of hours ; and secretion 

 cannot then be excited, even when the motor nerve is stimu- 



