128 PHYSIOLOGICAL CHEMISTRY. 



THE SPLITTING OF FATS. 



The general reactions of fats have been already referred to 

 and it has been shown that in general they may be broken up 

 by the action of water in the form of superheated steam : 

 C 8 H 5 (Cn H 2 ^iO 2 ) 8 + 3H 2 O = CsHsOsHs + aHC.H^CX 



The action of the pancreas in the emulsification of fats was 

 recognized as early as 1834 and in seeking for the cause of 

 this it was finally found to depend on a ferment reaction, and 

 subsequent soap formation. 



Lipase or Steapsin. The active principle in the pancreas 

 which accomplishes this fat splitting was first called steapsin 

 and afterwards lipase. The details of its behavior in the di- 

 gestion of fats will be explained in a following chapter. Be- 

 sides its constant occurrence in the pancreas, it has been found 

 in the blood, the liver and the kidney. More recently the 

 existence of lipase in many vegetable substances has been ob- 

 served and thoroughly studied. It has been found that it 

 hydrolyzes some of the simpler ethereal salts very readily and 

 on this behavior is based a method of recognition of conveni- 

 ent application. Of these ethereal salts ethyl butyrate is pos- 

 sibly the best, as it suffers but very slight change by the action 

 of water alone at ordinary temperatures. The fat-splitting 

 power, or enzyme strength, of various extracts may be com- 

 pared by noting the amount of the ethyl butyrate decomposed 

 in a given time under the influence of the extract. The extent 

 of hydrolysis of the ethereal salt is determined by titrating the 

 butyric acid liberated with dilute alkali. 



PROTEOLYTIC REACTIONS. 



While it is not possible to write equations illustrating accu- 

 rately the absorption of water in the digestion of proteins, as 

 may be done for the carbohydrates and the fats, yet there is 

 abundant evidence to show that water addition is in most 

 cases the characteristic preliminary change here also. The 

 action of superheated steam has been referred to in a former 

 chapter, but at the ordinary temperature certain proteolytic 

 changes take place which are the results of enzyme action. At 



