CARBOHYDRATES AND FATS. 797 



body proteids and fats; the larger the supply of fat, the more 

 effectively will the proteid 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 Fate of the Fat in the Tissues. The fat absorbed as 

 food may temporarily subserve 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, however, 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, peri- 

 toneum, etc. probably 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 Loeven- 

 hart (see p. 660). 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 constant by the diastatic enzyme of the liver. 

 After the action of the lipase we can only say that oxidation 

 takes place, but through how many stages is not known. 



Origin of the Body Fat. The views upon the origin of body 

 fat have undergone a number of changes in the last fifty or sixty 

 years, illustrating in an interesting way how development of our 

 experimental methods leads often at first to half-truths which are 

 corrected later by more extensive work. Dumas and others (1840) 

 held to the natural view that the fat of the body originates directly 

 from the fat of the food. Liebig, applying his more exact methods, 

 demonstrated that in some cases at least this source is insufficient 

 to account for all the fat. The fat yielded by the milk of a cow 

 for instance, may be greater in quantity than the fat contained 

 in the food. He also pointed out that the fat of each species of 

 animal is more or less peculiar, the fat of the sheep having a higher 

 melting point than pork fat, and both differing in composition from 

 the fat taken as food. "In hay or the other fodder of oxen no 

 beef suet exists, and no hog's lard can be found in the potato refuse 



