316 ESSENTIALS OF PHYSIOLOGY. 



such as pure olive oil, be shaken up with pancreatic juice, and the 

 mixture be kept at a temperature of 37 C., the fatty ester will be 

 hydrolysed, yielding fatty acid and glycerol, and the reaction of the 

 fluid will become acid. The agent which brings about this change is 

 an enzyme, lipase, which is a constituent of the pancreatic juice. Lipase 

 may be extracted from the fresh pancreas by glycerol, but not by water. 

 The fat-splitting action of lipase is greatly facilitated by the presence 

 of bile, taking place four or five times as rapidly when assisted by bile 

 as in its absence. This acceleration is due to the bile salts, which not 

 only reduce surface tension and so promote the admixture of the enzyme 

 and the fats, but also have the property of bringing fatty acids and 

 soaps into solution. 



The digestion of the fats is further assisted mechanically by the 

 formation of soaps. Some of the fatty acid, which is set free combines 

 with the alkalies of the intestinal contents to form soap. Segmental 

 contractions of the intestine lead to the mechanical subdivision of the 

 fats with the formation of an emulsion. Each fat droplet becomes 

 coated with a fine film of soap, which prevents it from coalescing with 

 others, and in this way the formation of a still finer emulsion is favoured, 

 and the fat is made more accessible to the enzyme. 



The Action of Pancreatic Juice on Milk. A milk-curdling ferment 

 has been described as occurring in the pancreatic juice, and it is a fact 

 that clotting of milk takes place when the. juice is mixed with milk at 

 the body temperature. It is doubtful, however, whether a separate 

 rennet ferment is present in the pancreatic secretion, and the milk- 

 curdling function has been ascribed by some authorities to trypsin. In 

 any case the clot stage is very brief, for the curd is rapidly dissolved by 

 the proteolytic action of trypsin ; moreover, the presence of rennin 

 in the pancreatic juice would seem to be unnecessary in view of the 

 active milk-curdling property of gastric juice. 



THE SECRETION OF PANCREATIC JUICE. 



In an animal with a permanent pancreatic fistula, a flow of juice is 

 seen to begin within five to twenty minutes after the ingestion of a 

 meal. The secretion is largely increased two or three hours later, when 

 the stomach contents are passing into the duodenum in largest amount, 

 and it comes to an end in about five hours. The following record of 

 two of Pawlow's experiments shows the rate of flow : 





