304 PHYSIOLOGY CHAP. 



Paton (1894-95), who brought forward other experimental data 

 agreeing with the theory that hepatic sugar is exclusively derived 

 from glycogen. The simplest and most direct proof of this theory 

 is given by Montuori (1895). He excised the liver of a newly 

 killed animal ; threw part into boiling water to arrest the pro- 

 duction of sugar, and kept another part for some time (24 hours) 

 at ordinary temperature, to allow the sugar to form freely. The 

 weight of the first and second parts of the liver was known. Both 

 parts were then boiled separately in a 1 per cent solution of 

 hydrochloric acid, so as to convert the whole of the contained 

 glycogen into sugar. On careful estimation of the amount of 

 sugar formed, he repeatedly found them to be approximately 

 equal in both parts of the liver. This shows that under these 

 conditions the glucose of the liver is formed exclusively from the 

 glycogen ; since if it were also formed from the proteins and 

 fats, more sugar would be produced in the portion of liver left to 

 itself for 24 hours. 



Montuori's results were confirmed by E. Cavazzani in Zuntz's 

 laboratory. He also found that the quantity of sugar that can 

 be collected from the excised liver did not increase on the addition 

 of peptones or glycerol (after Seegen's method). Weiss (1898), 

 on the other hand, with Bunge, confirmed Seegen's results on 

 repeating the experiments with an emulsion of gum and fat. 

 This induced Montuori (1899) to undertake new experiments to 

 ascertain whether fat added to the excised liver in a suitable form 

 would be partially converted into sugar. His results were entirely 

 negative. Hesse, Abderhalden, and Eona (1904), under identical 

 conditions with Weiss and Seegen, did not obtain the positive 

 results of these authors, but confirmed the negative conclusions 

 of Cavazzani and Montuori. It may therefore be concluded that 

 there is at present no evidence that the liver when excised from 

 the body is able to form sugar from any material other than 

 glycogen. 



IX. The fact that on steeping freshly excised liver from a 

 living animal in boiling water, the conversion of glycogen into 

 sugar is arrested, made Bernard refer this conversion to the work 

 of an enzyme, a kind of hepatic diastase. But his attempts to 

 isolate this enzyme, which were repeated by Hensen, led to no 

 conclusive results. 



In 1873 Wittich succeeded in extracting a highly active 

 ferment from the liver (when completely bloodless, washed and 

 pounded) by means of alcohol. 



Pavy (1894), by a method of extraction analogous to Wittich's, 

 confirmed his results, and isolated from the liver a specific enzyme 

 which determined the conversion of glycogen into glucose in vitro 

 with various intermediary products (dextrin, isomaltose, and 

 maltose). 



