916 NUTRITION AND HEAT REGULATION. 



other sources, but the former view must be reckoned among the 

 possibihties in enumerating the various functions that may be ful- 

 filled by the carbohydrate of the food. 



Nutritive Value of Fats. — The fats of food are absorbed into 

 the lacteals, chiefly as neutral fats — the so-called chyle fat. The 

 chyle fat is transported to the blood by way of the great thoracic 

 duct, and after it is poured into the blood it remains in the cir- 

 culation for a considerable time, being slowly picked out by the 

 tissues which can use it in their metabolic processes. Within 

 these tissues it is oxidized to supply the energy needs of the cells. 

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

 burnt outside the body — namely, CO, and Hfi — 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 



