v INTERNAL RESTITUTIVE SECRETIONS 301 



argued that this substance must be generally diffused in the body 

 like urea, and that its production could not be localised in a single 

 organ. 



In continuation of these researches Bernard (1850) demonstrated 

 the presence of sugar in the liver of mammals, birds, reptiles, 

 fishes, and molluscs. He further proved that the blood of the 

 hepatic veins invariably contained sugar during digestion ; that it 

 contained less when digestion was completed ; hardly any after a 

 long fast. After prolonged feeding of dogs with flesh, he estimated 

 the sugar content of the intestine and the portal blood, and found 

 none perceptible to reagents ; on the other hand, there was a con- 

 siderable amount in the blood of the hepatic veins and the liver. 



In order, however, to establish Bernard's theory of hepatic 

 glycogenesis (to which objections were raised by Figuier, Sanson 

 and Colin) upon a solid basis, it was necessary to exclude the 

 possibility that the sugar had been carried by the portal blood, the 

 liver merely having the task of storing it up and accumulating it, 

 as it does with other substances (arsenic, antimony, mercury, etc.). 

 The fundamental experiment which Bernard devised in 1855 for 

 this purpose, consisted in extracting the liver from the abdominal 

 cavity and irrigating it by the portal vein with a continuous 

 current of water. After 40 minutes' irrigation, he excised a bit 

 of the liver, boiled it, and found no sugar in the extract. After 

 24 hours the remainder of the liver was extracted, and was 

 found to contain much sugar. From this Bernard concluded 

 that the liver contains a material from which sugar is formed. 

 He further concluded that contact with the air is favourable to 

 the formation of new sugar, while it is on the other hand checked 

 by boiling. Since sugar can be formed in the liver of animals 

 fed exclusively on a flesh diet, Bernard concluded that it is manu- 

 factured in the liver at the expense of the nitrogenous protein, by 

 a process of fermentation. 



Soon after, however, and almost simultaneously, Hensen 

 (December 1856) and Bernard (March and June 1857) extracted 

 from the liver glycogen or animal starch, a substance similar to 

 vegetable starch or rather to dextrin, which is readily converted 

 into sugar by the influence of the salivary or pancreatic enzyme, 

 as the starch of barley is converted into sugar during germination 

 by the action of diastase. To separate glycogen, the liver of a 

 well-fed animal must be excised, chopped up, and steeped in 

 boiling water. After boiling, the fragments of liver are pounded 

 in a mortar to a paste, which is then extracted, neutralised, 

 filtered, and boiled again to get rid of the proteins, when an 

 opalescent extract is obtained, which is milky in appearance, and 

 remains unchanged by repeated filtration. On adding iodine the 

 extract stains red like erythrodextrin ; on heating the colour 

 disappears, to reappear on subsequent cooling. Troinmer's test 



