362 METABOLISM, NUTRITION AND DIETETICS 



molecule of aldol is formed, which by transposition of certain groups, 

 becomes butyric acid, the fourth member of the fatty acid series of 

 which acetic acid is the second member, and palmitic and stearic acids, 

 which form such important constituents of the ordinary body - fats, 

 the sixteenth and eighteenth members respectively. By oxidation aldol 

 becomes /3-oxybutyric acid, which by further oxidation yields aceto- 

 acetic acid, compounds already referred to in connection with diabetes 

 (p. 555). The following equations illustrate these reactions: 



= CH 3 .CH(OH) .CH 



Acctaldehyde. Acetaldehyde. Aldol. 



CH 3 .CH (OH) .CH 2 .CHO - CH 3 .CH 2 .CH a .COOH 



Aldol. Butyric acid. 



CH 3 .CH(OH).CH a .CHO+ O =CH 3 .CH(OH).CH,.COOH 



Aldol. j8-oxybutyric acid. 



CH S .CH (OH) .CH 2 .COOH + O = (CH 3 .CO) .CH a .COOH + H 2 O 



j8-oxybutyric acid. Oxygen. Aceto-acetic acid. Water. 



By reduction aceto-acetic acid is reconverted into /3-oxybutyric acid. 

 Other aldehydes can react in similar ways, and thus many of the other 

 fatty acids can be formed. 



It may be added that acetone (another of the so-called acetone 

 bodies which appear in the urine in diabetes mellitus) is easily obtained 

 from aceto-acetic acid by the splitting off of carbon dioxide. Thus : 



(CH 3 .CO).CH a .COOH =CH 3 .CO.CH 3 + CO 2 



Aceto-acetic acid. Acetone. Carbon dioxide. 



Formation of Fat (2) From Protein. Dry protein contains on 

 the average 16 per cent, of nitrogen and 50 per cent, of carbon, and 

 urea contains 46 per cent, of nitrogen and 20 per cent, of carbon. 

 Urea is therefore three times as rich in nitrogen as the protein from 

 which it is derived, but two and a half times poorer in carbon ; and 

 less than one-seventh of the carbon of protein will be eliminated 

 in a quantity of urea sufficient to carry off all the nitrogen. It 

 is probable that a portion of the remaining carbon may, after passing 

 through various stages, take its place as the carbon of fat. We 

 have seen that certain amino-acids derived from proteins can be 

 converted into dextrose, and that dextrose can be converted into 

 fat. So that the mere question whether carbon atoms or carbon 

 chains originally present in protein molecules are ever capable of 

 appearing in fat molecules can be straightway answered in the 

 affirmative. But it is still in doubt whether amino-acids can be 

 transformed into glycerin or into fatty acids, or into both, by 

 processes which do not involve the production of dextrose from 

 them. And in any case proof is required that the extent of the 

 transformation, let the steps be what they may, is great enough 

 to be satisfactorily demonstrated. In regard to this point it must 

 be said that absolutely flawless experiments to prove the direct 

 production of fat from protein seem still to be wanting. 



