NORMAL FAT METABOLISM 197 



amounts of food fat may by certain treatment be transported without con- 

 siderable change directly to the fat depots, evidence is available to show 

 that under normal conditions where the animal has free choice of food 

 and where the amount of fat ingested is not too large, the fat in the chyle 

 may be noticeably different from the fat in the intestine. Two factors 

 appear to be at work in the production of the differences: (a), selection 

 from the food fat of the more desirable or useful portions (generally the 

 lower melting), and (b) other changes either of the nature of additions 

 or of chemical changes saturation or desaturation which may alter 

 the composition considerably. With regard to the first factor selection 

 Munk has found that in dogs fed with lard the feces fat had a considerably 

 higher melting point than the fat fed. With regard to. the second factor 

 admixture or alteration during the passage from the intestine, Munk 

 and Rosenstein after feeding cetyl palmitate found the chyle fat to 

 consist of one part of triolein and six parts tripalmitin, with a melting 

 point of 30 C. Frank (1808), after feeding ethyl palmitate, found 36 

 per cent of olein in the chyle fat, and after feeding mutton tallow (m.p. 

 51.7 C.) obtained a chyle fat melting at 38 C. In these cases there was 

 an alteration in the direction of obtaining a lower melting fat. Bloor 

 (1913-14) obtained evidence of an alteration in the other direction, i. e., 

 the chyle fat having a higher melting point than the fat fed. After feed- 

 ing olive oil of which the constituent fatty acids had a melting point of 

 16 C. and an iodin number of 86, chyle fat was obtained with a melting 

 point of 30 C. and iodin numbers down to 72. Other evidence corroborat- 

 ing the above findings was furnished by Raper (1912-13). In most of 

 these cases the influence of lipoids present in the fasting 'chyle was excluded 

 so that we may conclude that the fat may be considerably modified during 

 the process of absorption. The modifications as found appear to be pur- 

 posive in that in all cases the tendency appears to be toward the production 

 in the chyle of a fat approximating the properties of the body fat of the 

 animal. As to the significance of these changes Frank was of the opinion 

 that there is an addition of body fat either by way of secretion into the 

 intestine or after the fat leaves the intestine. It has been shown by Leathes 

 (1909) that the liver has probably the power of desaturating the fatty 

 acids a power which all living cells may possess to some degree, and 

 there is a possibility that the intestinal cells can desaturate or saturate the 

 fatty acids during their passage through. The mechanism would allow 

 adaptive changes in the fats during absorption. 



Factors in Fat Digestion and Absorption. Pancreatic Secretion. 

 The pancreas is the main source of lipase in the intestine. The amount 

 of secretion, generally given at 500 to 600 c.c., is sufficient for the rapid 

 hydrolysis of at least its own weight of emulsified fat, and since the 

 amount of fat in the daily human diet does not often exceed 100 grams, 

 is greatly in excess of the needs. In the absence of pancreatic secretion. 



