NORMAL FAT METABOLISM 193 



of the reaction, using castor bean lipase. They found that, proceeding in 

 cither direction with the glycerid or with glycerol and oleic acid in the 

 proportions found in the natural glycerid the equilibrium point was 

 reached when about 40 per cent of the acid was combined. During the 

 synthesis the compounds formed were apparently mainly diglycerids. 

 During the hydrolysis with excess of water and near the beginning a 

 small amount of a lower glycerid was present, but as the action continued 

 the molecule was completely hydrolyzed. When only a small proportion 

 of water was present a greater proportion of mono- and diglycerids was 

 produced. Conversely when the synthesis is effected in the presence of 

 water more of the triglycerid is formed. Synthesis in the presence of 

 extra glycerol results as would be expected in a proportionately greater 

 combination of fatty acids with the formation cf more of the lower types 

 of glycerid although the diglycerid is probably still the main product. 



The pancreatic lipase, although secreted with the pancreatic juice in 

 water-soluble form, is with difficulty extracted from the gland by water. 

 Glycerol is generally used for the purpose and the result is a suspension 

 which may become inactive on filtration, indicating that the lipase is 

 probably not in true solution. 



Pancreatic lipase is secreted mainly in the active form, and its activity 

 is increased by the presence of bile (bile salts) and by many other sub- 

 stances as, for example, blood serum, soaps, saponins, alcohol, etc. 

 Its action is inhibited by cholesterol. Rosenheim has succeeded in sepa- 

 rating from the lipase of pancreatic extracts (glycerol) a co-enzyme with- 

 out which the enzyme is inactive. As is generally the case with co-enzymes 

 this one is heat-stable. Since the inactive enzyme is activated by blood 

 serum the assumption is made that the activating substance is a hormone 

 produced by the pancreas and secreted into the blood. 



Normally the provisions for the digestion of the fats in the intestine 

 are such as to insure practically complete splitting. Fat is delivered 

 to the intestine in small amounts when there is little fat in the food this 

 follows as a matter of course; when fat is present in large proportion 

 emptying of the stomach is slowed, whereby the same result is effected. 

 Lipase is abundant, being found both in the gastric secretion and in the 

 pancreatic and intestinal secretions. The amount in the pancreatic 

 secretion alone is sufficient to digest quickly several times the amount 

 of fat supplied in the ordinary diet. The gastric lipase, under 

 fayorable conditions, can digest considerable quantities, and even the 

 intestinal lipase can probably affect splitting of the daily quota of fat, 

 since in cases where the pancreatic secretion is lacking very little unsplit 

 fat is found in the feces. Emulsification by soap is an important factor in 

 the hydrolysis, and there is normally abundant provision for the forma- 

 tion of soap. There is always some free fatty acid in natural fats, and 

 the amount is increased by cooking and by the action of the gastric lipase, 



