534 METABOLISM, NUTRITION AND DIETETICS 



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, a polysaccharide 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. 715.) 



(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 con- 

 verted into dextrose by some influence which is restrained or de- 

 stroyed 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 are destroyed 

 at the temperature of boiling water. It ha.- been clearly shown 

 that the action is brought about by a diastatic enzyme, which some 

 writers call glycogenase, for it readily occurs when the minced liver 

 is mixed with chloroform water, and chloroform kills all living 

 tissues. Although blood contains a diastase in small amount, the 

 change does not depend essentially upon this, since the glycogen 

 also undergoes hydrolysis (glycogenolysis) to dextrose when all the 

 blood has been washed out of the organ. Lymph also contains a 

 diastase, but there is evidence that the post-mortem glycogenolysis 

 is chiefly due to an enzyme contained in the hepatic cells (an endo- 

 enzyme) (Macleod). The diastases in the blood and lymph seem 

 to be ' discards ' of the tissues which are on the way to destruction 

 or elimination (Carlson). The post-mortem change is to be regarded 

 as an index of a similar action which goes on during life: sugar in 

 the intact body is changed into glycogen ; glycogen is constantly 

 being changed into sugar. There is no reason to doubt that here, 

 too, the hydrolysis is effected by the endo-enzyme. It might be 

 supposed, indeed, that the adjustment of the two processes glyco- 

 gcnesis and glycogenolysis is simply a matter of the alteration of 

 the equilibrium in a reversible reaction (p. 338), according to 

 whether the dextrose content of the blood tends to rise or fall. If 

 the concentration of dextrose in the blood is increased, more dex- 

 trose might be expected to ' diffuse ' into the hepatic cells, whose 

 content of dextrose in proportion to glycogen would increase till 

 the equilibrium was restored by the conversion of the excess of 



