IQ2 TEXT-BOOK OF PHYSIOLOGY 



stages. Ever since the discovery by Cohnheim of the existence in the 

 intestinal juice of a substance termed by him erepsin, which is capable of 

 splitting proteoses and peptones into simple nitrogen-holding compounds, 

 there has been slowly developing the idea that normally during intestinal 

 digestion the proteoses and peptones are reduced by this agent to leucin, 

 tyrosin, histidin, arginin, aspartic acid, ammonia, etc., which in turn are 

 absorbed and transported by the blood direct to the tissues. The discovery 

 by Vernon of erepsin in pancreatic juice lends further support to this view. 



3. On fat. If pancreatic juice be added to a perfectly neutral fat 

 olein, palmitin, or stearin and kept at a temperature of about iooF. 

 (38C.), it will at the end of an hour or two be partially decomposed into 

 glycerin and the particular fat acid indicated by the name of the fat used 

 e.g., oleic, palmitic, stearic. The oil will then exhibit an acid reaction. 

 The reaction is represented in the following formula: 



C 3 H 5 (C 18 H 33 2 ) 3 + 3 H 2 = 3C 18 H 34 2 + C 3 H 5 (OH) 3 

 Triolein. Water. Oleic Acid. Glycerin. 



If to this acidified oil there be added an alkali, e.g., potassium or sodium 

 carbonate, the latter will at once combine with the fat acid to form a 

 salt known as a soap. The reaction is expressed in the following equation: 



Sodium Carbonate. Oleic Acid. Sodium Oleate. Carbonic Acid. 



Na 2 C0 3 + C 18 H 3i 2 - 2 NaC 18 H 83 2 + H 2 CO 3 



Coincident with the formation of the soap, the remaining portion of the 

 neutral oil will undergo division into globules of microscopic size, which are 

 held in suspension in the soap solution, forming what has been termed an 

 emulsion, which is white and creamy in appearance. The cause of this 

 minute subdivision of the fat and the necessity for it is unknown. It may 

 be assumed that by virtue of the subdivision a greater surface is exposed to 

 the action of the pancreatic enzyme and the digestion of the fat thereby 

 facilitated. The action of the pancreatic juice 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 spontane- 

 ously. The enzyme which produces the cleavage of the neutral fats has 

 been termed steapsin or lipase. The extent to which the cleavage of the 

 fat takes place in the intestine 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 Pavlov 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 excess of either starch, protein, 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 positively known that this is the case 

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

 the production of which is thought to be the special function of secretin. 

 The pancreatic juice at the moment of its discharge into the intestine does 

 not contain trypsin but trypsinogen. The transformation of the latter into 



