206 FUNCTIONS OF NUTRITION. 



It appears furthermore from the experiments of Weiss and Luch- 

 singer * that a similar increase of glycogen will take place in the liver 

 after the ingestion of glycerine (C 3 H 8 3 ), but not under 4he use of fat 

 or of the alkaline tartrates or lactates. 



There is accordingly every reason to believe that carbohydrates, when 

 taken with the food, are transported to the liver by the portal circula- 

 tion, and fixed in its substance under the form of glycogen. It makes 

 no difference, in this respect, whether they be taken as starch or as 

 sugar ; since starchy matters are transformed into glucose by digestion 

 in the intestine. It is under the form of glucose, therefore, that they 

 enter the portal circulation and reach the tissue of the liver. The con- 

 version of this substance into glycogen, as shown in a former chapter 

 (page 61), is essentially a dehydration. It is not possible to say in 

 what manner or by what influence this change takes place ; but it is 

 one of the simplest methods of transformation for organic substances, 

 and exactly the reverse of that by which glucose is produced from starch 

 in the intestine. 



Transformation of Glycogen into Glucose. The glycogen thus de- 

 posited in the liver from the products of digestion does not remain under 

 that form in the hepatic tissue. It is gradually reconverted into glucose, 

 and carried away into the general circulation. This is shown by the 

 fact that the liver always contains a small quantity of glucose, even in 

 the intervals of digestion, though none may be present in the blood of 

 the portal vein ; and that the blood generally contains about the same 

 quantity of glucose, though the supply of carbohydrates in the food be 

 temporarily suspended. The first fact was discovered by Bernard f in 

 1848. If a dog, cat, or other carnivorous animal be killed after several 

 days of an exclusive meat diet, the liver alone of all the internal organs 

 is found to contain glucose. The hepatic tissue, ground to a pulp and 

 boiled in a little water with an excess of sodium sulphate, to eliminate 

 the albuminous and coloring matters, will yield a filtered extract which 

 responds to Trommer's or Fehling's test, and enters into fermentation 

 on the addition of yeast. At the same time neither the contents of the 

 intestine, the blood of the portal vein, nor any other of the solid organs 

 give evidence of a similar ingredient. By the use of Fehling's test the 

 proportion of saccharine matter in the liver substance may be deter- 

 mined. 



The presence of glucose in the liver under these circumstances is 

 common to all animals so far as known. It has been found by Bernard 

 in the monkey, dog, cat, rabbit, horse, ox, sheep, birds, reptiles, and sev- 

 eral fish. If the fresh liver of man be examined after sudden death by 

 accident or violence, it is also found to contain sugar. 



The glucose thus produced in the liver originates by transformation 

 from the hepatic glycogen under the influence of a ferment. As the 



* Archiv fur die gesammte Physiologic, 1873, Band viii., p. 290. 



fComptes Eendus de P Academic des Sciences. Paris, 1850, tome xxxi., p. 571. 



