694 METABOLISM 



and resynthesis of neutral fat occurs for the same reason that similar 

 processes occur during the absorption and assimilation of protein. It 

 will be remembered that protein is entirely disintegrated in the intestine 

 into its so-called building stones. These are absorbed separately into 

 the blood, which carries them to the tissues, in which they become re- 

 synthesized to form the body protein. And so it appears to be in the 

 case of fats. The process, in other words, permits of the rearrangement 

 of fatty-acid molecules, as a result of which the newly formed fat is more 

 adaptable for use in the organism. It comes to be more like the char- 

 acteristic fat of the animal. There may be another reason for the proc- 

 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 con- 

 siderable 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 occur, 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 acid. 



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 



