RELATION OF PROTEINS TO CARBOHYDRATE METABOLISM. 389 



and only in special cases can we draw approximately accurate conclu- 

 sions. When, for example, the quotient in a case was especially high, 

 we could conclude that sugar was formed from fat ; if no nitrogen reten- 

 tion existed, with a carbohydrate-free diet. 



The property of protein of increasing the elimination of sugar is 

 considered as an important proof of the formation of sugar from protein. 

 In this regard those experiments are of special interest in which the 

 diabetic animal is allowed to starve until the urine is poor in sugar or 

 indeed free from sugar, and then by feeding with protein an abundant 

 elimination of sugar is produced. If we do not accept the view in this 

 case that the protein, but rather the fat, was the material from which 

 the sugar was produced, still we must admit either of a sugar-sparing 

 action due to protein or of a strong sugar formation from fat, incited 

 by the protein. 



A sparing in the sense that the protein is oxidized instead of the sugar, 

 and in this manner protects it, is naturally possible only under the sup- 

 position that the body can burn at least a part of the sugar, otherwise 

 there would be nothing to spare and nothing to protect from burning. 

 The assumption of such an indirect action of proteins is difficult to recon- 

 cile with the common, view of the inability of the body to burn sugar 

 in diabetes. LUTHJE l has communicated one experiment among others, 

 in which a dog with pancreas diabetes, whose weight before starvation 

 was 18 kilos, with nineteen days' starvation eliminated an average of 

 10.4 grams sugar for the last six days of starvation. By exclusive pro- 

 tein feeding the quantity of sugar per day could be raised to a maximum 

 of 123.6 grams, and as average it was 97.5 grams for the ten protein 

 days. The protein, therefore, had protected daily an average of 87 

 grams sugar from burning, which is hardly possible ; and if in the diabetic 

 animal we admit of this considerable power of burning sugar, the quotient 

 D:N becomes valueless as a measure of the quantity of sugar formed. 

 If, on the contrary, we admit of an indirect action of proteins in 

 that they incite a sugar formation from fat, perhaps by a certain very 

 important increase in the activity of the liver, we are .opposed by the 

 great difficulty that, according to known laws of metabolism, the pro- 

 teins do not raise the fat metabolism, but rather diminish it. The pro- 

 tein displaces a corresponding quantity of fat from the metabolism, 

 and if the fat were the only source of sugar then in this case we would 

 expect a diminished elimination of sugar instead of an increased one. 

 Nevertheless the above action of protein upon sugar elimination is much 

 more easily explained by the assumption of a sugar formation from 

 protein than from fat. 



1 Deutsch. Arch. f. klin. Med., 79. 



