322 



VETERINARY PHYSIOLOGY 



lining the intestine, under the influence of an acid. This is 

 absorbed into the blood in which it is carried round the 

 circulation, and, on reaching the pancreas, stimulates it to 

 secrete (fig. 154). It has been shown that the injection 

 into a vein of an extract, made with dilute hydrochloric 

 acid, of the lining membrane of the upper part of the small 

 intestine, leads to a flow of pancreatic juice. Secretin is 



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auj 



Fig. 154. — To show the Mode of Action of Secretin and of the vagus nerve 

 on the secretion of the pancreas and the activation of ti'ypsinogen by 

 enterokinase. 



not destroyed by boiling, and is soluble in strong alcohol. 

 It is therefore not of the nature of an enzyme. 



(6) Nervous Control. — But, while secretin seems to play 

 so important a role, it has been found that stimulation of 

 the vagus nerve, after a latent period of several minutes, 

 increases pancreatic secretion, so that it must be concluded 

 that the process of secretion is, to a certain extent, under 

 the control of the nervous system. 



The influence of the j)ancreas in the general metabolism 

 will be considered later (p. 357). 



