METABOLISM 199 



of the bile. In the lymph and later in the blood plasma, the 

 products of fat digestion appear not as fatty acids and glycerol, 

 but as recombined fat in a soluble form, giving to the blood 

 plasma a turbid character, in case large amounts of fat have 

 been eaten. In this form in the blood plasma, the absorbed 

 and recombined hydrolytic products of fat food may become 

 oxidized on reaching the muscle cells in a similar way to that 

 by which the glucose is oxidized. In case the fat carried in the 

 blood plasma is not required to be burned to furnish the energy 

 supply of the body, the soluble fat in the blood plasma becomes 

 reconverted again into the ordinary insoluble form and is 

 deposited as fat globules which eventually form the fatty or 

 adipose tissue of the body. 



Body Fat and Milk Fat. — The occurrence in body fat and 

 also in milk fat of certain characteristic fats eaten as food has 

 led to the belief held by some that fat food is absorbed in the 

 form of an emulsion of unhydrolyzed fat. The fat of hogs which 

 have been fed on cottonseed meal has been shown to give. the 

 tests for cottonseed oil. Also the milk fat of cows which have 

 been fed on sesame oil cake responds to the tests for sesame oil. 

 It is generally accepted, however, that the presence of such 

 fats in the body and milk is not incompatible with the idea 

 that all fat food is hydrolyzed into fatty acids and glycerol. 

 The reversible nature of the enzymatic reaction, especially of 

 lipolytic enzymes, is well established ; and this reversible reaction 

 may take place even during the passage of the hydrolytic 

 products through the wall of the digestive tract, so that, when 

 the assimilated products of digested fat food first appear in the 

 lymphatic capillaries, they are in the form of recombined fat, 

 and not of the separate hydrolytic products. This recom- 

 bined fat synthesized from the hydrolytic products so imme- 

 diately would thus appear in the lymph and blood plasma and 

 then in the muscle cells or in the milk in the same form in 

 which it was eaten. 



When the absorbed products of fat food are thus metabolized 

 into the fat of blood plasma, and this fat is not used as fuel to 



