224 IV. CONVERSION OF FAT TO CARBOHYDRATE 



in the case of a 55 kg. dog. Such figures compare with values of 29.3 g. for 

 nitrogen, 107.7 g. for sugar and a D:N of 3.61 : 1 for a dog weighing 40 kg., 

 on the fourth day of fasting, and the second day of phlorhizin, as reported 

 by Mandel and Lusk.^^ Lusk^^ denied that the figures of Hartogh and 

 Schumm could be reproduced under proper experimental conditions. Grafe 

 and Wolf^' reported similar high D : N ratios which exceeded 5 : 1 and even 

 reached 11.6 after the ingestion of cereal, in the case of a diabetic patient 

 presumably on an exclusively protein fat diet which was free from carbo- 

 hydrates. Lusk^ suggests that such ratios may be the result of surreptitious 

 ingestion of carbohydrate food. He cites the results of experiments of 

 Greenwald*^ and of Allen and DuBois^^ in which similar high values were 

 found in the case of diabetic patients. When the patients were confined to a 

 private room where the food could be checked, ratios approaching 3.65:1 

 were promptly obtained.^^-^^ The data would seem to indicate unquestion- 

 ably that, in fasted diabetic animals, there is no evidence, based upon the 

 D : N ratio, that fat serves as a source of carbohydrate. 



In the case of fat-fed diabetic animals, also, there is no experimental evi- 

 dence to confirm the transformation of fat to carbohydrate. Thus, Lusk,^ 

 Takao,''^ and Deuel and Milhorat^^ are unanimous in reporting that fat 

 feeding does not increase the D:N ratio of dogs. On the other hand, 

 Soskin^" reported an increased D : N ratio in three depancreatized dogs, two 

 of which had received lecithin and the third olive oil. On this basis, it was 

 suggested that the extra sugar originated from the fatty acids. However, 

 in ten tests no rise in the D : N ratio occurred after 50 g. of fat had been 

 given. In six of the negative tests, the D:N varied between 2.99 and 2.68; 

 these figures are in excellent agreement with the value of 2.8: 1 for fasting 

 depancreatized dogs postulated by Minkowski. ^^ Moreover, Page and 

 Young^^ did not find evidence of an increase in the D : N ratio following the 

 injection of phosphatide into phlorhizin-diabetic dogs. 



A third criterion in which the D : N ratio has been employed in assembling 

 evidence as to whether or not fat can be changed into carbohydrate is the 

 efTect of conditions known to increase fat metabolism on the carbohydrate 

 level. If the metabolism of fat is associated with a marked conversion of 



85 A. R. Mandel and G. Lusk, Am. J. Physiol, 16, 129-146 (1926). 



86 G. Lusk, Ergeh. Physiol, 12, 315-392 (1912). 



" E. Grafe and C. G. L. Wolf, Deut. Arch. klin. Med., 107, 201-235 (1912). 

 «8 I. Greenwald, J. Biol Chem., 16, 375-377 (1913). 



89 F. M. Allen and E. F. DuBois, Arch. Internal Med., 17, 1010-1059 (1916). 



90 S. Soskin, Biochem. J., 23, 1385-1390 (1929). 



9' O. Minkowski, Naunyn-Schmiedeberg's Arch, expil Pathol Pharmakol, 31, 85- 

 189 (1893). 



92 1. H. Page and F. G. Young, Biochem. J., 26, 1528-1531 (1932). 



