558 METABOLISM, NUTRITION AND DIETETICS 



oxyacid oxycaproic acid, CH 3 .CH 2 .CH 2 .CHOH.CH a .COOH, which is 

 then by further oxidation converted, with loss of two carbon atoms, 

 into butyric acid. The oxidation process may then start afresh on 

 the /3 group of butyric acid. On the long carbon chains of the higher 

 fatty acids this operation may be repeated again and again, the chain 

 losing two atoms of carbon at each attack. If this represents what 

 occurs in the normal metabolism, the groups cut off may then and there 

 undergo the fate of the ships isolated by a successful application of jthe 

 manoeuvre alluded to, complete destruction that is to say, oxidation 

 to the end products carbon dioxide and water, a portion of the energy 

 of the fatty acid being thus liberated at each oxidation of the ft group. 

 Eventually a fatty acid or acids with very few carbon atoms will be 

 left. There is some reason to think that acetic acid (and perhaps 

 similar simple acids) may be one of the normal stages in the decom- 

 position. Thus, butyric acid may first yield by oxidation of the 

 ft group the oxyacid /3-oxybutyric acid, CH 3-CHOH.CH 2 .COOH, 



which by further oxidation of the /3 group and the cutting off of the a 

 and carboxyl groups would give CH 3 .COOH, or acetic acid. 



If this is the general course of the oxidation of the fatty acids in 

 the body, it is to be assumed that numerous intermediate stages 

 unrepresented in such a simple scheme may exist. Thus it is known, 

 as has been mentioned more than once in other connections (p. 553) , 

 that /3-oxybutyric acid by oxidation yields aceto-acetic acid, by 

 losing from the j8 group two atoms of hydrogen which unite with 

 oxygen to form water. A molecule of aceto-acetic acid contains 

 the elements of two molecules of acetic acid minus the elements of 

 one molecule of water. It is therefore possible that aceto-acetic 

 acid, if it is a normal stage in the katabolism of fatty acids, yields 

 by its hydrolysis as a further step acetic acid, according to the 

 equation 



CH 3 .CO.CH 2 .COOH + H 1 O=2(CH 3 .COOH). 



Aceto-acetic acid. Acetic acid. 



It is worth while, perhaps, to point out once more that even the 

 relatively simple products now arrived at are not necessarily at 

 once completely oxidized to their end products. That, it is to be 

 assumed, will depend upon the needs of the organism. Acetic acid, 

 for example, when added to blood and perfused through the sur- 

 viving liver, can be transformed into aceto-acetic acid, and may 

 thus become the starting-point of new syntheses. 

 f The Liver and Fats.^-fThe liver seems to play an important part in 

 the metabolism of fat, as it does in the metabolism of carbo-hydrates 

 and of proteins. It contains an oxidizing ferment, ^-oxybutyrase 

 (or^^li^droxybutyrase), which transforms $-oxybutyric acid into 

 aceto-acetic acidj (Dakin). This oxidation appears to occur in the 

 normal as well as in the diabetic organism. ( The liver seems also to 

 possess the power of transforming aceto-acetic acid into acetone! a 

 reaction which does not involve an oxidation, and this may also DC 

 accomplished by means of an enzyme. But it is not at all likely 



