PANCREATIC JUICE. 237 



The evidence that the pancreatic juice has this power is unques- 

 tioned, and that it is due to the presence of an enzyme is proved 

 by the fact that boiling destroys this power, and by the further 

 fact that it cannot be due to bacteria, for antiseptics do not affect 

 it ; nevertheless, the knowledge as to its properties is very meager. 

 Its action upon fats is very rapid, and it is probable that " it is 

 capable of splitting up all the fat of a full meal in the ordinary 

 time of digestion within the body." The presence of bile, by 

 virtue of its contained bile-salts or bile-acids, increases its activity, 

 and this is still greater when hydrochloric acid is present. 



An interesting fact in connection with the secretion of the pan- 

 creatic juice is that its composition varies according to the nature 

 of the food ingested. Thus, if fat is present in considerable quan- 

 tity, there will be produced a corresponding amount of the lipolytic 

 enzyme, whereas if the diet consists largely of muscular tissue, 

 trypsin will preponderate. There is no reason to believe that this 

 variation in the composition of digestive juices is confined to the 

 pancreas ; it is doubtless equally true of other digestive organs that 

 their products vary with the character of the food. 



Emulsifying Power of Pancreatic Juice. One of the offices 

 performed by the pancreatic juice is to make an emulsion of fats 

 which form an important part of the food. This action is not 

 due to any enzyme, but to the formation of fatty acids by the 

 steapsin ; indeed, this is regarded by some authorities as the chief 

 office of the lipolytic enzyme. The splitting up of fat is in and 

 of itself, according to this theory, of no great physiologic impor- 

 tance, inasmuch as only a part of the fat is thus split up, but the 

 fatty acids which result, together with the fatty acids which the fats 

 themselves contain, bring about the emulsification of the main por- 

 tion of the fat, which process is, according to some authorities, so 

 essential in preparing it for absorption. Of the theories propounded 

 to explain fat absorption, we shall speak later (p. 261). 



The fatty acids resulting from the decomposition of the fat unite 

 with the alkaline salts in the small intestine, probably those of 

 the bile and the intestinal juice rather than those of the pancreatic 

 juice, and form soaps, which, aided by the peristaltic movements 

 of the intestine, convert the fat into an emulsion. The proteids 

 of the pancreatic juice take no part in this emulsifying process, 

 but it is very materially aided by the presence of the bile, inas- 

 much as bile and pancreatic juice acting together split up fat much 

 more quickly than the juice alone. 



In what manner soaps act to emulsify fats is not known. Some 

 have supposed that the soap forms a film around the fat-globules 

 after they have been finely divided, which prevents their uniting ; 

 but the formation of such a film has never been demonstrated. 

 Moore, in Schiifer's Physiology, says that the very fine subdivision 

 of the fat and the increased viscosity of the menstruum occasioned 



