THE CARBOHYDRATES AND THEIR METABOLISM 251 



venous blood becomes poorer in glucose. The process then reverses. The 

 glycogen in the liver cells becomes hydrolyzed and a stream of glucose starts 

 into the blood. Apparently there must exist a very delicately adjusted 

 physicochemical relationship between the glucose concentration of the 

 portal blood, the glycogen content of the liver, and the glucose concentra- 

 tion of the hepatic vessels. 



The capacity of the liver to store glycogen is enormous. Schoendorf 

 (1903 (&)) showed that the liver of dogs may contain as much as 18.7 per 

 cent of glycogen, and Otto (1891) showed that rabbit's liver may contain 

 as much as 16.8 per cent of glycogen after ingestion of large amounts of 

 carbohydrates. The liver of a man weighing about 70 kilos weighs ap- 

 proximately 2000 grams. On the basis of the above figures, we can readily 

 see that it can hold as much as 300 grams of glycogen, which is considerably 

 more carbohydrate than the average man consumes in any one meal. 



The liver, therefore, through its glycogenetic function acts as a won- 

 derful regulator of the sugar in the blood. It prevents any marked fluctua- 

 tions in the concentration, and above all, any sudden increases in the sugar 

 content, which would be followed by loss of sugar through glucosuria. 



The utilization of glucose by the muscle cells occurs as soon as its 

 absorption from the intestinal canal begins (Lusk, 1912-1915). Ap- 

 parently the body cells burn glucose with greater ease than any other food- 

 stuff, for, when glucose is present in abundance, the combustion of fat is 

 stopped almost completely, and that of protein is reduced to an absolute 

 minimum. Glucose in the body burns to CO 2 and H 2 O, according to the 

 following reaction: 



C 6 H 12 O G -f 6 O 2 6 CO 2 -f 6 H 2 O 



From this we see that when glucose is oxidized a certain volume of oxy- 

 gen is required, and for every volume of oxygen used, a corresponding vol- 

 ume of carbon dioxid is given off. The ratio between the volumes of 



CO 



CO 2 and O 2 is known as the Respiratory Quotient. The value of -p 



^2 



in this case equals 1. In the combustion of no other foodstuff does the 



CO.> 

 Respiratory Quotient equal 1. When fat burns the -^p quotient is 0.707, 



and when protein burns, the quotient is 0.801. 



In Lusk's experiments on dogs, forty-five minutes after glucose in- 

 gestion, the respiratory quotient was 0.99, showing that glucose burnt 

 almost exclusively. 



If the absorption of glucose from the intestinal canal still continues, 

 we have a third factor brought into play, namely its conversion into fat. 



In normal individuals, during the process of glucose absorption from 

 the intestinal canal, we have a series of three outlets which are operating 

 to prevent its accumulation in the blood. Schematically we may repre- 



