902 



PHYSIOLOGY 



ferment formed in the liver-cells. Which of these two processes pre- 

 ponderates depends, in the normal animal, on the percentage amount 

 of sugar in the blood which is circulating through the organ. 



On account of the importance of glycogen as a reserve material it 

 is produced and stored up in almost all growing tissues, to be utilised 

 in their subsequent development. Thus it is found in large quantities 

 in the placenta during a certain period, in fcetal muscles, and in various 

 other situations. It is found in yeast, in oysters, and in the muscles 

 of the body generally. In fcetal muscles it may amount to as much 

 as 40 per cent, of the total dried solids. The glycogen of the 

 adult muscle is apparently utilised during muscular w r ork, and 

 diminishes in amount with activity of the muscle. In adult muscles 

 it never reaches anything like the percentage which is found in the liver. 

 The average amounts found by Schondorf in the different tissues were 

 as follows : 



THE UTILISATION OF SUGAR IN THE BODY 



Arterial blood is always found to contain between 0'12 and 0'15 per 

 cent, of sugar in the form of glucose. The same amount is found 

 whether the blood be taken from an animal after a heavy carbo- 

 hydrate meal or from one in a condition of complete starvation. The 

 constancy of the sugar content of the blood suggests that this substance 

 is a necessary constituent of the circulating fluid, necessary, that is 

 to say, for the nutrition of the tissues. That it is being used up in all 

 the processes of the body is shown by the immediate alteration in the 

 respiratory quotient which occurs when the food is changed from a 

 mixed diet to one consisting mainly of carbohydrate. An important 

 factor in the maintenance of a constant sugar content in the blood is 

 the reconversion of the stored-up glycogen of the liver into sugar. 

 The glycogen is not, however, the sole source of the sugar, since in 

 complete starvation the sugar content of the blood remains constant 

 even after the last traces of glycogen have disappeared from the liver. 

 If the liver be cut out of the body or removed from the ciici'lation, 

 during the few hours that the animal survives there is a steady diminu- 



