CARBOHYDRATES AND FATS. 915 



The final products of the oxidation are the same as when fat is 

 burnt outside the body namely, fO 2 and H 2 O and a corre- 

 sponding amount of energy must be liberated. Speaking generally, 

 then, the essential nutritive value of the fats is that they furnish 

 energy to the body, and, from a chemical standpoint, they must 

 contain more available energy, weight for weight, than the proteins 

 or the carbohydrates. In a well-nourished animal a large amount 

 of fat is found normally in the adipose tissues, particularly in the 

 so-called "panniculus adiposus" beneath the skin, in the folds 

 of the peritoneum, etc. Physiologically, this body fat is to be 

 regarded as a reserve supply of nourishment. When fatty food 

 is eaten and absorbed in excess of the actual metabolic processes 

 of the body, the excess is stored in the adipose tissue as fat, to be 

 drawn upon in case of need as, for instance, during partial or 

 complete starvation. A starving animal, after its small supply 

 of glycogen is exhausted, lives entirely upon body proteins and 

 fats; the larger the supply of fat, the more effectively will the 

 protein tissues be protected from destruction. In accordance with 

 this fact, it has been shown that when subjected to complete 

 starvation a fat animal survives longer than a lean one. Our 

 supply of fat is called upon not only during complete abstention 

 from food, but also whenever the diet is insufficient to cover the 

 oxidations of the body, as in deficient food, sickness, etc. 



The Intermediary Metabolism of the Fat. The fat absorbed 

 as food may subserve in general several different purposes: (1) It 

 may be oxidized with the formation of heat energy. (2) It may 

 be stored in the tissues as part of the body fat. (3) It may be 

 synthesized with other substances to form some more complex 

 constituent of the body, such as lecithin. (4) According to some 

 authors, it may serve under certain conditions as a source of sugar. 

 This latter suggestion is not supported by convincing experiments. 

 The final fate of the fat in the body is, however, to be oxidized to 

 water and carbon dioxid. The nature of the processes involved 

 is not understood. It is generally believed that the first step 

 is the splitting of the fat into fatty acid and glycerin under the 

 influence of the lipase found in so many of the tissues of the body. 

 The fat that lies in the storage tissues skin, peritoneum, etc. 

 does not undergo oxidation in these places. In times of need it is 

 absorbed and distributed to the more active tissues, and in this 

 initial process of solution it is probable that a regulative influence is 

 exerted by the lipase as suggested by Loevenhart (see p. 744); 

 that is, by its reversible action this enzyme may control the output 

 of fat to the blood, as the supply of sugar in the blood is kept con- 

 stant by the diastatic enzyme of the liver. After the action of the 

 lipase we can only say that oxidation takes place, but through how 



