104 LECTURE VI. 



cides with an increase in the amount of carbohydrates. We shall come 

 back to this point later on. 



Let us now follow the course of the fat, which is received by the animal 

 organism in its food, as it passes through the alimentary canal and through 

 the paths of absorption. Fat passes the entrance to the alimentary tract 

 (i.e., the mouth) in a perfectly unaltered condition. Saliva has no action 

 upon it, and, although saponification begins in the stomach, the extent to 

 which this is accomplished is still much in dispute. 1 The digestion of fat 

 while in the stomach is of small moment, for the action of the ferment is 

 soon lessened, and eventually stops entirely, on account of the acid 

 reaction of the stomach juices. The lipase requires, moreover, for its 

 maximum efficiency that the fats shall be in an emulsified state, a con- 

 dition which is rarely fulfilled in the stomach. The action of the gastric 

 juices is, however, of indirect importance, because the fat of meat is set 

 free by the digestion of the connective tissue. For these reasons there 

 is no absorption worth mentioning of the fats while they remain in the 

 stomach. The real digestion of fat sets in when it reaches the intestine. 

 Here, first of all, it undergoes a purely physical change. By the action 

 of the free fatty acids, and on account of the presence of the alkali salts 

 in the intestinal and pancreatic juices and the bile, the fat is first of all 

 subdivided. The fatty acids, which are deposited everywhere between 

 the tiny particles of fat, react with the alkaline carbonates present. Soaps 

 result which now tear the tiny particles apart, making them still finer, a 

 process which is assisted by the carbon dioxide set free by the neutraliza- 

 tion. An emulsion is formed. The purpose of this process may be two- 

 fold. We can imagine that the epithelial cells of the intestine absorb 

 these fine globules directly in the same manner as is done by the plant 

 cells. Again, it is perfectly possible that the chief advantage of the 

 emulsion is to present an enormously large surface to the lipase, thus 

 facilitating its action. 



We are absolutely certain that ingested fat is decomposed into fatty 

 acids and glycerol. The fatty acids unite as much as possible with the 

 alkali present, thus forming soaps. A question yet to be settled is the 

 extent of saponification; i.e., how much of the total fat in the food is 

 entirely decomposed. Although Pfltiger 2 assumes that the hydrolysis 

 must be complete, i.e., that only fatty acids and glycerol are available for 

 assimilation, other investigators believe that only a portion of the fat is 



1 Cash: Arch. Anat. Physiol. 1880, 323. Ogata: ibid. 1881, 515. Volhard: Miin- 

 chen. med. Wochschr. 5 and 6 (1900); Z. klin. Med. 42, 414; Verhandl. deut. Naturf. 

 Aerzte, 1901, II, 2d half p. 43. A. Zinsser: Hofmeister's Beitrage, 7, 31 (1905). 

 A. Fromme: ibid. 7, 51 (1905). 



2 Pfliiger's Arch. 80, 111 (1900); ibid. 81, 375 (1900); ibid. 82, 303 (1900); ibid. 

 85, 1 (1901); 86, 1 (1901); 89, 211 (1902). 



