THE DIGESTIVE SYSTEM. 313 



digested substances which enters the intestine has a yellowish colour and 

 a semi-fluid consistence, and is immediately subjected to the action of 

 the pancreatic juice and bile. The secretion of Brunrier's glands and 

 the intestinal juice are also mixed with the duodenal contents, but the 

 digestive action of the former is not known to have any importance, and 

 that of the latter has its chief value in the later stages of the digestive 

 process. The action of the pancreatic juice and bile must therefore be 

 considered in the first place. 



THE COMPOSITION OF PANCREATIC JUICE. 



Pure pancreatic juice may be obtained from an animal either by 

 means of a temporary fistula, made by introducing a cannula into the 

 pancreatic duct, or by a permanent fistula. In the dog there are 

 two ducts, the larger of which opens into the duodenum about an 

 inch below the entry of the bile duct. Pawlow's method of making 

 a permanent fistula is to cut out a patch of the duodenal wall 

 with the opening of the duct in its centre, stitch lip the gap in the 

 duodenum, and suture the patch with the opening of the duct into 

 the abdominal wall. 



The pancreatic juice obtained in this way is a clear, limpid fluid, 

 having a specific gravity of about 1007 and a strongly alkaline 

 reaction. The degree of alkalinity is such that equal volumes of 

 gastric juice and pancreatic juice neutralise each other. The con- 

 centration of pancreatic juice varies considerably, but it contains 

 on an average about 4 per cent, of solids. These consist of nucleo- 

 protein, enzymes or their precursors, and inorganic salts. The 

 chief salt is sodium carbonate. 



THE FUNCTIONS OF PANCREATIC JUICE. 



The action of the pancreatic juice on the constituents of the food 

 may be studied in test tubes, using either the secretion obtained from 

 a fistula, or an artificial juice made by adding a glycerol extract of the 

 fresh gland to a solution of sodium carbonate of such a strength that 

 the mixture contains 0*5 per cent, of the carbonate. 



The Action of Pancreatic Juice on Proteins. Pure pancreatic juice, 

 obtained directly from the pancreatic duct, without contact with the 

 intestinal mucous membrane, has no action on proteins. If, however, 

 the juice has flowed over the duodenal mucous membrane or has been 

 mixed with intestinal juice, it is strongly proteolytic. The pure juice 

 contains a substance, trypsinogen, which is the precursor of a proteolytic 



