CABROHYDRATES AND FATS. 917 



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

 The fat that Hes 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. 739); 

 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 

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

 chain of the fats (stearic acid = CH3(CH2)i6COOH) 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, /S-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 = CH3CHOHCH2- 

 COOH. By oxidation this yields aceto-acetic acid, CH3COCH2- 

 COOH, and this by loss of CO2 is converted to acetone, CH3- 

 COCH3. The occurrence of these bodies is in accord with the view 

 of a serial oxidation of the fatty acids furnished by the fats. 

 Knoop* has given experimental evidence for the view that the oxi- 

 dation 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, C15H31CH2CH2COOH, oxidation at the beta-carbon 

 may be assumed to give first a beta-ketonic acid, C15H31COCH0- 

 COOH, which, by further oxidation, loses two carbon atoms, with 

 the production of CO2 and H2O, and yields a saturated fatty acid, 

 C15H31COOH, of simpler structure. 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 inter- 

 mediate 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 

 * Knoop, -'Hofmeister's Beitriige," 6, 150, 1904. 



