198 INTERMEDIATE METABOLISM 



1. There would be no reason for the existence of pan- 

 creatic Hpase if such saponification were not necessary. 



2. When a mixed emulsion of fats and hydrocarbon oils, 

 such as turpentine, is introduced into the intestine fats 

 only are absorbed. For absorption, therefore, something 

 more than division into a fine particulate state is necessary. 

 The substance must go into solution, and this in the case 

 of fats can only occur by saponification. 



3. When fats are introduced into the intestine they 

 'appear in the chyle as neutral fats. Synthesis with 



glycerine from some source unknown has therefore occurred 

 in the intestinal wall. 



4. Certain esters introduced into the intestine appear in 

 the thoracic duct modified as regards both their basic and 

 their acid constituents. Such a change could only occur 

 after saponification. 



The strongest evidence for the theory that fats may be 

 absorbed as such is the fact that when fats are administered 

 stained they appear stained in the thoracic duct. But 

 this is due to the stains being soluble in the soaps. 



The evidence therefore points to a saponification pre- 

 ceding and resynthesis succeeding absorption. Whether 

 the two changes are brought about by different ferments or 

 by the same ferment acting reversibly according to the 

 laws of mass action we do not know. 



The same problem occurs in the passage of fats between 

 the blood and the cell for the purpose of storage or com- 

 bustion. If such a transference necessitates saponification 

 we must assume the ubiquitous existence of hpolytic and 

 hpo genie enzymes. 



The existence of fat in the body may be discussed under 

 three headings. 



1. The Fat Depots. — These are principally the sub- 

 cutaneous tissues, omentum and peritoneum. The high 

 percentage of fatty acid (95 per cent.) indicates that the fat 

 exists in the form of simple triglycerides. Its low iodine 

 number shows the high proportion of saturated fatty acids. 



