538 METABOLISM, NUTRITION AND DIETETICS 



That levulose can be changed into dextrose in the body is indi- 

 cated by the observation that after extirpation of the pancreas in 

 dogs the administration of levulose is followed by an increase in 

 the excretion of dextrose nearly equal to the amount of levulose 

 ingested. It is also stated that, when the surviving liver of a 

 normal dog is perfused with a suspension of washed blood-corpuscles 

 to which levulose has been added, dextrose accumulates in the blood 

 and levulose disappears from it. 



It has not hitherto been proved that the fatty acid component of 

 the food fats can be converted into glycogen. But a fatty acid, 

 propionic acid, is capable of complete transformation into dextrose 

 when given either by the mouth or subcutaneously to dogs under 

 the influence of phlorhizin (Ringer) . Many other bodies are known 

 to influence the formation of glycogen by ' sparing ' substances 

 which are true glycogen-producers, but their carbon does not actu- 

 ally take its place in the glycogen molecule. It has been shown that 

 proteins can directly form glycogen or sugar apart from carbo- 

 hydrate groups contained in the protein molecule. For the proteins 

 of meat, gelatin, and casein are capable of forming 60 per cent, of 

 their own weight of dextrose in diabetic metabolism, and even the 

 end-products of pancreatic digestion of meat yield so much sugar 

 that the greater part of it must have come from the amino-bodies, 

 and not from a sugar-group in the protein. When given to dogs 

 with total phlorhizin glycosuria (p. 551), glycin and alanin are 

 completely, glutamic and aspartic acids in great part (corresponding 

 to about three carbon atoms of their respective molecules), converted 

 into dextrose (Lusk and Ringer), and there is no reason to doubt 

 that when such substances are produced by hydrolysis of protein 

 in the normal body, and are not all utilized in rebuilding the bio- 

 plasm, a portion of the surplus, after deamidization, can be trans- 

 formed into glycogen. 



Extra-Hepatic Glycogen. While the liver in the adult (con- 

 taining as it does from 2 to 10 per cent, of glycogen, or even, with 

 a diet rich in sugar or starch, more than 18 per cent.) may be looked 

 upon as the main storehouse of surplus carbo-hydrate, depots of 

 glycogen are formed, both in adult and fcetal life, in other situations 

 where the strain of function or of growth is exceptionally heavy 

 in the muscles of the adult (0-3 to 0-5 per cent, of the moist skeletal 

 muscle, or on a carbo-hydrate regimen 0-7 to 3-7 per cent.), in the 

 placenta, in many developing organs in the embryo (muscles, lungs, 

 epithelium of the trachea, oesophagus, intestine, ureter, pelvis of 

 kidney, and renal tubules). The foetus, however, is not, compared 

 with the adult, especially rich in glycogen. In the adult under 

 favourable circumstances the absolute amount of glycogen in the 

 muscles may be several times greater than that in the liver, and 



