328 THE METABOLISM OF THE CARBOHYDRATES 



form glycogen? The only explanation that can be offered of 

 this apparent anomaly is, that in the animals which have been 

 experimented on, there exists no digestive ferment capable of 

 hydrolysing the lactose. Such, indeed, has been shown by 

 Ernst Weinland ( 6 ) to be the case. Whereas, a watery extract 

 of the intestinal mucosa of all animals which take milk in their 

 food (e.g. the young of all mammalia, and omnivorous animals 

 all through life) can invert lactose, 1 no such ferment is present 

 in watery extracts of the intestinal mucosa of herbivorous animals 

 (hens and rabbits). 2 



The subcutaneous injection of cane-sugar or of lactose 

 does not increase glycogen formation, nor can these ' sugars be 

 oxidised in the organism i.e. they pass unchanged into the 

 urine when subcutaneously injected. From this we may con- 

 clude that neither of these sugars is directly transformable into 

 glycogen, and that there is no inverting ferment in the blood 

 capable of producing dextrose and Isevulose from them. With 

 maltose, however, different results are obtained. Intravenous 

 injection, in moderate doses at least, is not followed by the 

 appearance of maltose in the urine, for there is present, in blood 

 plasma, a ferment capable of inverting maltose, and the dextrose 

 thus formed is converted into glycogen. Of course, in the normal 

 digestion of starch, &c., most of the maltose will have been 

 already inverted by the maltase contained in the Succus entericus 

 before it is absorbed, but there is reason to believe that some 

 passes as such into the portal blood (Pavy 10 ). 



The only carbohydrates which the hepatic cells can directly 

 convert into glycogen, therefore, are dextrose and laevulose, and 

 possibly, galactose. These are also the sugars which are fermentable 

 by yeast. The glycogen produced in each case is, chemically, the 

 same, and is undoubtedly produced by a synthetic process, several 

 of the monosaccharide molecules fusing together with the loss of 

 a corresponding number of water molecules ; thus : 



nC 6 H 12 6 = (CH 10 0> + nH 2 



(Monosacch.) (Polysaccli.) 



1 This action is due to the extracts containing a hydrolytic ferment called 

 lactase, which acts specifically on lactose. 



2 Several workers have reported glycogen formation in dogs after feeding 

 with lactose, but, as Pfliiger points out, none of the reported cases is abso- 

 lutely convincing. 



