620 GENERAL METABOLISM [CH. XLI. 



acid in his liver into aceto-acetic acid, and then finally burn that 

 acid into carbonic acid and water. The diabetic patient breaks 

 down at this very point; he is able to form a certain amount of 

 aceto-acetic acid, but this passes unchanged into his urine, or if any 

 is changed at all, it is not into carbonic acid and water, but into 

 acetone instead. 



Our next question is whether during life fat may be converted 

 into carbohydrate ? In plants, the utilisation of fats by the embryo 

 during germination has been studied. When growth begins enzymes 

 are formed which hydrolyse fats, and v. Fiirth found in his work 

 on the oil in the seeds of the sunflower and castor-oil plant that 

 the changes which occur consist in an increase in the saponification 

 value and a lowering in the iodine and acetyl values. The increase 

 in the saponification value indicates a fall in the molecular weight 

 of the fatty acids, that is to say, the formation of lower fatty 

 acids from higher ones has occurred ; the lowering of the iodine and 

 acetyl values indicates that it is the unsaturated linkages and the 

 hydroxylated carbon atoms that have been the weak places where 

 the cleavage has occurred. But beyond these observations there is 

 nothing known of the metabolism of fats in plants ; certainly any 

 evidence that they are transformed into carbohydrates is lacking. 



The evidence that the transformation of fats into carbohydrates 

 can occur in animals is also indirect or unsatisfactory. Pflliger 

 argued that in glycosuria following extirpation of the pancreas, or 

 phloridzin administration in dogs, large quantities of fat are con- 

 verted into sugar. This was an assumption based upon the idea 

 that none of the sugar could have been formed from protein. This 

 view does not accord with the observations and opinions of others 

 who have worked at the subject, and for many years Pfliiger fought 

 in his usual strenuous manner for his own view that protein can 

 never be a source of sugar. However, facts were too strong 

 for him, and in almost the last paper he wrote before he died he 

 withdrew it. 



We have already seen the chemical difficulties of explaining how 

 sugar can be converted into fat, but it is a fact nevertheless. The 

 difficulty of explaining the converse change is equally great; still 

 in spite of this difficulty and in spite of the unsatisfactory nature 

 of any proofs that this actually occurs during life, it cannot be 

 maintained that the formation of sugar from fatty acids is impossible ; 

 for we have already seen that the formation of sugar from certain 

 amino-acids such as alanine, which are of protein origin, has been 

 proved to occur. Amino-acids deprived of their amino-group are fatty 

 acids ; alanine, for instance, minus its amino-group, is propionic acid. 

 The ultimate fate of lower fatty acids derived from fats can hardly 

 be different from that of those which are derived from proteins. 



