252 A MANUAL OF VETERINARY PHYSIOLOGY 



are remarkable for the amount of protein present in them ; they 

 vary in amount in different animals — for example, 9 per cent, in 

 the dog, and 0-9 per cent, in the horse. In addition to these, the 

 pancreatic secretion is remarkable for containing three enzymes, 

 which act on different food substances. 



Mechanism of Pancreatic Secretion. — The pancreatic secretion 

 is influenced by special secretory nerves ; stimulation of the vagus 

 or splanchnic may, after a long latent period, give rise to a 

 secretion, though it is not yet settled whether these fibres produce 

 it during the act of digestion. The outpouring of the acid chyme 

 from the stomach into the duodenum at once gives rise to a 

 secretion of pancreatic juice, and at one time it was supposed the 

 acid acted on the secretory nerves and produced a secretion 

 reflexly, for this action could be reproduced experimentally. 

 Bayliss and Starling, however, demonstrated the remarkable 

 fact that if an extract of the mucous membrane of the duodenum 

 or jejunum be made by scraping the bowel, and acting on it 

 by weak hydrochloric acid, a substance may be obtained which 

 when injected into the blood produces a profuse pancreatic 

 secretion. To this internal secretion of the intestinal cells they 

 gave the name Secretin, the nature of which has not been deter- 

 mined. Two facts are clearly established — first, that it is not a 

 ferment, as it is not destroyed by boiling ; and, secondly, that 

 acid is an essential part of the process, for if the mucous mem- 

 brane of the bowel be extracted with either water or saline solution, 

 secretin is not obtained. It is the acid chyme, therefore, acting 

 on the mucous membrane of the intestine which produces 

 secretin ; this is absorbed by the blood, and thus produces its 

 specific action on the pancreas. Within a minute or two of 

 introducing a 0-4 per cent, hydrochloric acid into the duodenum 

 pancreatic juice flows into the intestine. The acid produces the 

 same effect if introduced into the jejunum, but not into the 

 ileum. 



Secretin is not a protein ; it is not destroyed, as stated above, 

 by boiling, and it is soluble in alcohol and ether. Prosecretin 

 exists in the intestinal mucous membrane ; it may be extracted 

 with physiological salt solution, and though unable itself to 

 promote pancreatic secretion, it may be converted into an active 

 secretion by the action of acid or by boiling. Secretin from one 

 animal will increase the pancreatic flow in another, either of the 

 same or of a different species. 



As a secretion can be obtained from the pancreas either by 

 stimulation of certain nerves or by introducing into the blood a 

 specific chemical substance, it would appear that under normal 

 conditions both processes may be operating in its production, 

 and that there may be, as in the case of the gastric juice, two parts 



