METABOLISM 193 



sorbed carbohydrate food. With an abundance of such food 

 the amount of glycogen reaches its maximum of 10 per cent 

 of the weight of the hver, in man. A gradual conversion of the 

 liver glycogen into glucose is constantly going on in order to 

 maintain the constant supply of o.i per cent of glucose in the 

 general venous circulation. If the supply of carbohydrate food 

 is diminished or cut off, this constant conversion of glycogen 

 into glucose gradually exhausts the supply in the hver and it 

 may fall to practically nothing. So far as is known, however, 

 there is no passage of absorbed carbohydrate food into the 

 general circulation except through the form of liver glycogen. 

 The liver is thus not only a storehouse of carbohydrate food 

 material, but is a kind of regulating reservoir by which a vary- 

 ing supply of absorbed carbohydrate food is passed on to the 

 general circulation in a constant supply of o.i per cent of the 

 blood. Without going into detail, which would involve the 

 discussion of yet unsettled questions, it may be stated that car- 

 bohydrate food of a pentose nature derived from pentosans in 

 vegetable foods probably passes through the form of liver gly- 

 cogen and reaches the general circulation as glucose. 



Oxidation of Glucose. — What now is the fate of the constant 

 supply of glucose furnished by the liver to the general circula- 

 tion? The hepatic vein leads to venous capillaries w^hich ter- 

 minate in the muscle cells. In this way the glucose product of 

 carbohydrate food reaches the ultimate cells of the animal and 

 in these cells the oxidation takes place by which the energy of 

 the carbohydrate food is liberated. By means of the arterial 

 blood system leading from the lungs the muscle cells receive also 

 a supply of oxygen in the form of oxyhcemoglobin of the arterial 

 blood. Within the cell the oxyhaemoglobin gives up its oxygen 

 to the glucose brought by the venous blood and oxidation of the 

 glucose takes place in accordance with the reaction, 



CeHisOe + 6 O2 -> 6 CO2 + 6 H2O + energy 



Oxidizing enzymes are probably the agents which produce this 

 reaction. The reaction does not take place as simply as in- 



