916 NUTRITION AND HEAT REGULATION. 



many stages is not known. It seems probable that the long carbon 

 chain of the fats (stearic acid = CH 3 (CH 2 )i 6 COOH) is deprived 

 in succession of its carbon atoms by oxidation, with the formation 

 of simpler 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, /3-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 is usually regarded as the source of the other two, as may be 

 inferred from their formulas. /3-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 . Other observers incline to the view that the aceto- 

 acetic acid is the primary product formed in the metabolism and 

 that the oxybutyric acid arises from it by reduction. The occur- 

 rence of these bodies is in accord with the view of a serial oxidation 

 of the fatty acids furnished by the fats. Knoop* has given experi- 

 mental evidence for the view that the oxidation takes place at the 

 beta-carbon, and that by a series of such beta-oxidations the long 

 carbon chain may be reduced, by the loss of two carbon atoms at a 

 time, to simpler fatty acids. Thus, in stearic acid, Ci 5 H 3 iCH 2 CH 2 - 

 COOH, oxidation at the beta-carbon may be assumed to give first a 

 beta-ketonic acid, Ci5H 3 iCOCH 2 COOH, which, by further oxida- 

 tion, loses two carbon atoms, with the production of CO 2 and H 2 O, 

 and yields a saturated fatty acid, Ci 6 H 3 iCOOH, of simpler struc- 

 ture. On this theory if, as is the case with the fatty acids of animal 

 fat, there is an even number of carbon atoms in the molecule to 

 start with, all of the simpler acids formed by the process of beta- 

 oxidation will also have an even number of carbon atoms. This is 

 the case with the butyric acid which so far represents the concrete 

 example of these intermediate stages, and the same fact is observed 

 for the fatty acids found in milk. It is to be borne in mind that 

 butyric acid and its oxyacid may be derived theoretically, at least, 

 from proteins as well as fats. As has been shown in the previous 

 pages, the amino-acids formed from the proteins may suffer deami- 

 nization in the body, leaving behind an oxy- or ketonic acid which 

 may then behave as do the similar acids formed by oxidation of the 

 higher fatty acids. Experiments have demonstrated that in this 

 way oxybutyric acid may be derived from a protein source. 



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 

 * Knoop, "Hofmeister's Beitrage," 6, 150, 1904. 



