190 PHYSIOLOGICAL CHEMISTRY 



it will lay on reserves of fat. There is evidence thus that carbo- 

 hydrates may be converted into fat in the body, although it 

 seems that the reverse process does not take place, at least it is 

 very questionable. Since amino acids may be converted into 

 carbohydrates, they also may be fat formers. 



Light has been thrown upon the mechanism of fat oxidation 

 in the body in various ways. Ordinarily the fatty acids are 

 burned completely to C0 2 and 2 . By introducing into the or- 

 ganism compounds in which a fatty acid side chain is attached 

 to a benzene ring, the last step in this destruction of the side 

 chain is prevented and the nature of the resulting substance may 

 be studied. Such compounds in which the side chain has an 

 even number of carbon atoms are oxidized, and the side chain 

 destoyed with the exception of two carbon atoms. From 

 phenylbutyric. acid, phenyl acetic is produced. This substance 

 is conjugated with glycocoll and excreted as phenyl aceturic 

 acid, a compound of phenyl acetic and glycocoll analogous to hip- 

 puric acid (q.v.). If the original side chain contains an uneven 

 number of carbon atoms, the side chain is oxidized away, and 

 benzoic acid remains, which is conjugated with glycocoll and 

 excreted as hippuric acid. From these facts it is evident that 

 the side chains are oxidized so that not one carbon atom, but 

 two are removed at each step. 



Thus it is believed that the fatty acids from the fats also are 

 oxidized two carbon atoms at a time, the final products normally 

 being converted completely into carbon dioxide and water. The 

 acetoacetic acid CH 3 CO CH 2 COOH, /?-oxybutyric CH 3 

 CHOH CH 2 COOH and acetone which appear in the urine in 

 the advanced stages of diabetes, when the organism is so severely 

 affected that its powers of oxidation are impaired are believed to 

 be largely a product of the incomplete oxidation of fatty acids, 

 though acetoacetic has been shown to arise also from certain of 

 the amino acids. 



Metabolism of Inorganic Material. The metabolism of inor- 

 ganic material assumes an aspect somewhat different from that 

 of the organic substances, for the reason that inorganic sub- 



