342 IV. DIGESTION OF LIPIDS OTHER THAN FATS 



likewise been demonstrated by Sehoenheimer and Hilgetag, 34 apparently 

 has an explanation similar to that for cetyl alcohol. 



The question which naturally arises is Avhether the lipid is actually 

 "secreted" by the walls of the large intestine or whether its origin is merely 

 to be traced to the fatty material resulting from desquamated intestinal 

 epithelia. Later experiments of Sperry 602 indicate that the latter ex- 

 planation is incorrect. In these tests, not only was the lipid content of 

 the mucosa too small to account for the quantity of lipid present in the 

 feces, but the proportion of the lipid occurring in the mucosa varied from 

 that known to originate in the several portions of the gastrointestinal 

 tract. Moreover, a smaller amount of lipids was found in the mucosa 

 of dogs subjected to ileostomy than in that of normal dogs. Finally, it 

 is believed that the metabolic activity of the mucosa rather than its cur- 

 rent lipid content is a gauge of the quantity of lipid excretion. These 

 results lead one to question whether any considerable portion of intestinal 

 lipids arises from desquamated cells. 



Another possible source of the fecal lipids might be bacterial synthesis 

 in the lower gut. Although some lipids may be newly formed as a result 

 of bacterial action, bacterial lipids probably do not account for more than 

 40% of the total. 603 Moreover, the ratio of liquid to solid fatty acids is 

 similar to that obtaining in the non-bacterial lipids. This same investi- 

 gator 604 later reported analogous results as regards the distribution of the 

 lipids in the excretions of bile-fistula dogs, in which the lipid output was 

 two to three times that of normal dogs. It is likewise probable that the 

 fecal cetyl and stearyl alcohols do not owe their formation to bacterial 

 synthesis. 



(S) The Effect of the Food Ingested 



Under ordinary conditions the excretion of lipids in the feces remains 

 quite constant, and is little influenced by the nature of the fat ingested. 

 However, when the dietary fat is incompletely digested, as is the case of 

 high-melting fats such as mutton tallow, deer fat, oleostearine, and com- 

 pletely hydrogenated animal and vegetable fats, sufficient of the dietary 

 fat may remain unabsorbed to alter completely the quantity and the rela- 

 tive composition of fecal fat. For a discussion of the digestibility of fats, 

 the reader is referred to Chapter III. 



602 W. M. Sperry, J. Biol. Chem., 96, 759-768 (1932). 



603 W. M. Sperry, J. Biol. Chem,, 81, 299-319 (1929). 



604 W. M. Sperry, ./. Biol. Chem., 85, 455-463 (1929-1930). 



