FAT METABOLISM 725 



ess. It will be remembered that lecithins, which constitute the most 

 important of the fatty substances of the cell itself, are mixed glycerides 

 that is to say, are compounds containing a variety of fatty acids. The 

 rearrangement of the molecules of neutral fat which occurs during ab- 

 sorption may be the first step in the transformation of fat into lecithin. 



In order to throw further light on the question, Bloor has performed a number of 

 interesting experiments in which the chemical properties of fats before and after 

 absorption were compared. The criteria which he took were melting point, iodine 

 value, and mean molecular weight; the melting point representing the solidity of the 

 fat, and the iodine value, its degree of unsaturation that is, the number of double 

 links in the fatty-acid chain. It was found that during absorption very considerable 

 changes occur in these two characteristics; for example, when fat with high melting 

 point and low iodine value was fed, the fat in the thoracic lymph was of distinctly 

 lower melting point and higher iodine value. When fat with a low melting point and 

 a high iodine value was fed, the reverse change occurred, for the melting point of 

 the thoracic lymph fat was higher and the iodine value lower. These results' could be 

 explained as due in the first case to the addition of oleic acid to the fat during its 

 synthesis in the intestinal epithelium, and in the second case to the addition of some 

 saturated fatty acid. 



When a fat consisting mainly of glyceride and saturated fatty acid, but with a 

 low melting point, was fed, the addition of oleic acid was still found to occair, as 

 judged from the iodine value. This indicates that the change is, not merely in order 

 that the melting point of the absorbed fat may be lowered, but also for some chemical 

 reason. In a fourth series of experiments, a lowering of iodine value occurred after 

 feeding with cod-liver oil, which contains a high percentage of glycerides of highly 

 unsaturated fatty acids. 



Evidently, then, the intestine possesses the power of modifying the com- 

 position of fat during its absorption, and this modification is apparently 

 of such a nature that it causes a change toward the production of a 

 uniform chyle fat, presumably characteristic of the animal body. The 

 changes are probably greater than could be produced by admixture of 

 the absorbed fat present in the normal fasting chyle, but the source of 

 the oleic acid or of the saturated acid required for this synthesis is at 

 present unknown. 



Regarding the transference of the synthesized fat globules from the 

 epithelial cells to the central lacteal it is believed, with Schafer, that 

 leucocytes play an important role. They engulf the fat globules and 

 carry them to the lacteal where they break down and liberate the glob- 

 ules. In support of this view Clark and Clark have observed, after injec- 

 tion of fats into the tails of tadpoles, that leucocytes pass out from the 

 blood vessels and accumulate around the oil globules, ultimately absorb- 

 ing the latter and then wandering to near-by lymph vessels into which 

 apparently they disgorge their loads of fat. 



