CARBOHYDRATES AND FATS. 827 



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 nof 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. 681). 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. It seems 

 probable that the long carbon chain of the fats (stearic acid = CH 3 - 

 (CH.,) 16 COOH) is deprived in succession of its carbon atoms by 

 oxidation, with the formation of simple fatty acids, but little 

 positive evidence has been obtained of intermediate products. 

 Perhaps the most significant fact known bearing upon this point 

 is that under conditions which involve a large destruction of fat 

 in the body, as in starvation, fevers, and especially in diabetes, 

 /9-oxybutyric acid together with aceto-acetic acid and acetone are 

 excreted in the urine. These three substances are designated as 

 the acetone bodies, and their appearance in the urine makes the 

 condition known as acetonuria. The oxybutyric acid may be 

 regarded as the source of the other two, as may be inferred from 

 their formulas, ^-oxybutyric acid = CH 3 CHOHCH 2 COOH. By 

 oxidation this yields aceto-acetic acid, CH 3 COCH 2 COOH, and 

 this by loss of CO 2 is converted to acetone, CH 3 COCH 3 . The 

 evidence seems to show that the oxybutyric acid arises from the 

 fats, and it represents possibly one of the simpler fatty acids formed 

 in the intermediate metabolism of the fats. 



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 



