DIGESTION. 28 T 



into it, was discovered by Claude Bernard in the following way: he fed 

 a dog for seven days with food containing a large quantity of sugar and 

 starch; and, as might be expected, found sugar in both the portal and 

 hepatic veins. And this dog was fed with meat only, and, to his sur- 

 prise, sugar was still found in the hepatic veins. Repeated experiments 

 gave invariably the same result; no sugar being found, under a meat 

 diet, in the portal vein, if care were taken, by applying a ligature on it 

 at the transverse fissure, to prevent reflux of blood from the hepatic ve- 

 nous system. Bernard found sugar also in the substance of the liver. 

 It thus seemed certain that the liver formed sugar, even when, from the 

 absence of saccharine and amyloid matters in the food, none could be 

 brought directly to it from the stomach or intestines. 



Excepting cases in which large quantities of starch and sugar were 

 taken as food, no sugar was found in the blood after it had passed through 

 the lungs; the sugar formed by the liver, having presumably disappeared 

 by combustion, in the course of the pulmonary circulation. 



Bernard found, subsequently to the before-mentioned experiments, 

 that a liver, removed from the body, and from which all sugar had been 

 completely washed away by injecting a stream of water through its blood- 

 vessels, will be found, after the lapse of a few hours, to contain sugar in 

 abundance. This post-mortem production of sugar was a fact which 

 could only be explained in the supposition that the liver contained a 

 substance, readily convertible into sugar in the course merely of post- 

 mortem decomposition; and this theory was proved correct by the dis- 

 covery of a substance in the liver allied to starch, and now generally 

 termed glycogen. We may believe, therefore, that the liver does not 

 form sugar directly from the materials brought to it by the blood, but 

 that glycogen is first formed and stored in its substance, and that the 

 sugar, when present, is the result of the transformation of the latter. 



Quantity of Glycogen formed. Although, as before mentioned, gly- 

 cogen is produced by the liver when neither starch nor sugar is present 

 in the food, its amount is much leas under such a diet. 



Average amount of Glycogen in the Liver of Dogs under various Diets 



(Pavy). 

 Diet. Amount of Glycogen in Liver. 



Animal food, 7. 19 per cent. 



Animal food with sugar (about J Ib. of sugar daily), . 14.5 

 Vegetable diet (potatoes, with bread or barley-meal), . 17.23 " 



The dependence of the formation of glycogen on the food taken is 

 also well shown by the following results, obtained by the same experi- 

 menter: 



