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2 o2 TEXT-BOOK OF PHYSIOLOGY. 



may then be said to consist in the cleavage of the neutral fats into 

 fatty acids and glycerin, after which the formation of the soap and 

 the division of the fat takes place spontaneously. The enzyme 

 which produces the cleavage of the neutral fats has been termed 

 steapsin. The extent to which the cleavage of the fat takes place in 

 IHTintestine has not been definitely determined. There are some 

 who think the amount is relatively small, while others consider that 

 it is large, practically all of the fat undergoing this decomposition, 

 with the formation of soap and glycerin prior to their absorption. 



According to Pawlow, the relative amounts of the pancreatic 

 enzymes produced are conditioned by the character and amounts 

 of the food principles consumed. Thus, if chyme contains an ex- 

 cess of either starch, proteid, or fat, there is a corresponding increase 

 in the amount of either amylopsin, trypsin, or steapsin produced. 

 The pancreas apparently adapts its activities to the character of 

 the food. Though it is probable that each enzyme is a derivative 

 of a special zymogen, it is only positively known that this is the case 

 with trypsin. This enzyme is a derivative of the zymogen, trypsin- 

 ogen. yfThe pancreatic juice at the moment of its discharge into 

 the intestine does not contain trypsin but trypsinogen. The trans- 

 formation of the latter into the former is accomplished, according 

 to Pawlow, by a special ferment secreted by the epithelium of the 

 small intestine and termed enterokinase./f 



The rapidity with which pancreatic juice in the presence of bile 

 and hydrochloric acid (under conditions such as are present in the 

 duodenum) can develop sufficient fatty acid to form an emulsion was 

 determined by Rachford to be two minutes. The activity of steapsin 

 is thus shown to be very great. 



Physiologic Action of the Intestinal Juice. The part played 

 by the intestinal juice in the digestive process is yet a subject of dis- 

 cussion, as the results obtained by different observers are in some 

 respects contradictory, due to the fact that animals, including human 

 beings, have been the subjects of experimentation. Notwithstanding 

 the actions of saliva, gastric and pancreatic juice, there yet remain 

 in the food saccharose, maltose, and lactose, three forms of sugar 

 which are believed by most observers to be non-assimilable and 

 therefore require some change before they can be absorbed and 

 assimilated. An extract of the intestinal mucous membrane or the 

 intestinal juice of a dog, added to a solution of saccharose, will in a 

 very short time convert it into dextrose and levulose, which together 

 constitute invert sugar. The enzyme by which this inversion is 

 nothing definite is known as to its nature, has been 

 Tubbey and Manning state that the human intes- 

 tinal juice as obtained by them has the same action. In the case 

 of intestinal fistulae reported by Busch, which were supposed to be 



