550 VI. OCCURRENCE OF LIPIDS IN THE ANIMAL 



of carbohydrate from protein can be considered as constituting equally 

 valid evidence for fat formation and for carbohydrate synthesis. 



A number of methods can be employed for demonstrating the production 

 of carbohydrate from protein. The most effective include the use of di- 

 abetic subjects (diabetes mellitus, pancreatic, phlorhizin, or alloxan di- 

 abetes) for quantitative determinations, estimation of the glycogen 

 deposition (particularly in the liver), and investigation of the effect of the 

 substance in preventing or reducing ketonuria. 



(a) The Formation of Glycogen or Glucose, a'. Experiments with Pro- 

 tein: According to Lusk 110 Claude Bernard was of the opinion that glycogen 

 could originate from protein. Voit 156 had a similar viewpoint, except that 

 he believed that the protein molecule was ruptured into two main fragments 

 without the liberation of any considerable amount of energy. One of these 

 fragments, which was the nitrogenous portion, was rapidly oxidized, as 

 indicated by the prompt elimination of the nitrogenous end-products in the 

 urine. The nitrogen-free fragment, which contained the major part of the 

 potential energy, could be temporarily stored either as carbohydrate or as 

 fat until it was used for energy. 



The first experimental demonstration of carbohydrate formation from 

 protein was that of Wolffberg, 157 who gave carbohydrate-free meat powder 

 to fowls previously fasted for several days to remove the glycogen. The 

 appearance of considerable quantities of glycogen in the liver and muscles 

 was taken as evidence of the conversion of protein to carbohydrate. Kulz 158 

 reached a similar conclusion. In 1910, Pfliiger and Junkersdorf 159 re- 

 ported convincing evidence of the transformation. After having denied the 

 validity of the proof for this change for many years, Pfliiger became con- 

 vinced when it was demonstrated that dogs, previously depleted of liver 

 and muscle glycogen by a ten-day fast followed by the injection of phlo- 

 rhizin, stored considerable quantities of glycogen after large amounts of 

 codfish had been given. The liver glycogen increased from a control value 

 of 0.1% to an average of 6.5% (maximum, 9.9%) after the ingestion of 

 codfish, while the muscle glycogen rose from 0.2 to 1.0%. Since the codfish 

 contained only inappreciable amounts of carbohydrate (0.03%), and since 

 fat was without effect on the glycogen store, the only interpretation possible 

 is that the carbohydrate originated from protein. 



156 C. Voit, Z. Biol, 28 [n.s. 10], 245-292 (1891). 



167 S. Wolffberg, Z. Biol, 12, 266-314 (1876). 



188 E. Kulz, in Festschrift fUr Carl Ludwig, Marburg, 1891, p. 83; cited by G. Lusk, 

 The Elements of the Science of Nutrition, 4th ed., Saunders, Philadelphia-London, 1928, 

 p. 206. 



159 E. Pfliiger and P. Junkersdorf, Arch. ges. Physiol. (Pfluger's), 181, 201-301 (1910). 



