METABOLISM, NUTRITION AND DIETETICS 511 



hydrates of the food, passing into the blood of the portal vein in 

 the form of dextrose, are in part arrested in the liver, and stored 

 up as glycogen in the hepatic cells, to be gradually given out again 

 as sugar in the intervals of digestion. The proof of this statement 

 is as follows : 



Sugar is arrested in the liver, for during digestion, especially 

 of a meal rich in carbo-hydrates, the blood of the portal contains 

 more sugar than that of the hepatic vein. Popielski on the 

 basis of experiments in which he fed with known quantities of 

 sugar dogs whose inferior vena cava and portal vein had been 

 united by an Eck's fistula, and determined the amount of sugar 

 which passed into the urine, estimates the quantity of sugar 

 kept back by the liver at from 12 to 20 per cent, of the whole. 

 In the liver there exists a store of sugar-producing material 

 from which sugar is gradually given off to the blood, for in the 

 intervals of digestion the blood of the hepatic vein contains more 

 dextrose (2 parts per 1,000) than the mixed blood of the body or 

 than that of the portal vein (about i part per 1,000). When 

 the circulation through the liver is cut off in the goose, the 

 blood rapidly becomes free, or nearly free, from sugar (Min- 

 kowski). And a similar result follows such interference with 

 the hepatic circulation as is caused by the ligation of the three 

 chief arteries of the intestine in the dog, even when the animal has 

 been previously made diabetic by excision of the pancreas (p. 518). 



The nature of the sugar-forming substance is made clear by 

 the following experiments : (i) A rabbit after a large carbo- 

 hydrate meal, of carrots for instance, is killed and its liver rapidly 

 excised, cut into small pieces, and thrown into acidulated 

 boiling water. After being boiled for a few minutes, the pieces 

 of liver are rubbed up in a mortar and again boiled in the same 

 water. The opalescent aqueous extract is filtered off from the 

 coagulated proteins. No sugar, or only traces of it, are found 

 in this extract ; but another carbo-hydrate, glycogen, an isomer 

 of starch giving a port-wine colour with iodine and capable of 

 ready conversion into sugar by amylolytic ferments, is present in 

 large amount. (See Practical Exercises, p. 608.) 



(2) The liver after the death of the animal is left for a time 

 in situ, or, if excised, is kept at a temperature of 35 to 40 C., 

 or for a longer period at a lower temperature ; it is then treated 

 exactly as before, but no glycogen, or comparatively little, can 

 now be obtained from it, although sugar (dextrose) is abundant. 

 The inference plainly is that after death the hepatic glycogen 

 is converted into dextrose by some influence which is restrained 

 or destroyed by boiling. This transformation might theoretically 

 be due to an unformed ferment or to the direct action of the 

 liver-cells, for both unformed ferments and living tissue elements 



