NOKMAL FAT METABOLISM 201 



less diffusible. On the other hand, the earlier theory of absorp- 

 tion of fat as such has secured some additional support from the observa- 

 tions of Green ami Skaer that fats can penetrate for considerable distances 

 into the stomach walls of animals, confirming on animals the much earlier 

 observation of Schmidt that fat penetrates readily into plant cells, 

 especially if it contain a little free fatty acid. The ability of certain types 

 of animal tissue cells to engulf foreign particles, including fats, has been 

 shown by Evans, just as the phagocytic white blood cells are known to do. 

 (The part which these same white blood cells take in fat absorption, while 

 known to be large for the individual cell, is not believed to be important 

 in the aggregate. ) However, even in plants a preliminary hydrolysis 

 would seem to be necessary since in fat seeds, such as the castor bean, 

 hydrolysis is known to take place before the fat is utilized. Even so, 

 hydrolysis produces another kind of insoluble substance the fatty acid 

 which, however, is different and probably essentially so in that in the 

 presence of alkali it becomes water soluble. To what extent fat passes 

 the intestinal walls as fatty acid bile being the ferry, as has been sug- 

 gested by Mathews cannot be determined. Xeither can it be said what 

 factors determine whether the digested fat shall pass directly into the blood 

 by way of the portal system or indirectly by way of the thoracic duct. In 

 the former case it passes directly to the liver, and in the latter it avoids it. 

 It seems quite certain that esters of the fatty acids which cannot be 

 hydrolyzed in the intestine and so rendered water-soluble and also oily 

 substances of other kinds which cannot be made water-soluble are rejected 

 no matter what their other properties may be nor how intimately they may 

 bo mixed with the fats. Water solubility of the absorbed products seems 

 to be as essential for the fats as for other food substances. The mechanism 

 for excluding substances which are not water-soluble is perfect, presumably 

 because such substances could not possibly be handled in the organism. 



Fat in the Blood 



Alimentary Lipemia. The study of the blood brings us one step 

 nearer to the actual seats of metabolism than that of the urine and other 

 waste products. It is the great distributing system of the body. The 

 recognition of these facts has turned the attention of most investigators 

 to the blood, with the result that thereby much has been added to our 

 knowledge of metabolism. Because of the greater difficulty of their study 

 tho discoveries regarding the fats have as usual rather lagged behind those 

 of the other foodstuffs, although a good deal has been accomplished. 

 Methods for fat determination in foods and tissues have been adapted for 

 use with blood, and new methods have been devised especially suited to 

 use with small amounts of blood, so that processes can be followed in 



