258 ABSORPTION OF THE FOOD. 



and heat and work are the result of this oxidation. The various 

 stages through which they pass are not all known, but as to some 

 there seems little doubt. Thus the formation of dextrose and 

 levulose, during digestion and absorption, and the deposition of 

 the greater part of these in the liver and muscles as glycogen, are 

 generally accepted; but as to what changes take place in the 

 glycogen there is a difference of opinion. 



" Theory of Claude Bernard. The opinion advanced by this 

 distinguished physiologist, who, in the year 1848, discovered that 

 sugar'was formed in the liver, and in 1857 that it had its origin 

 in glycogen, was that the dehydration of the dextrose by the liver- 

 cells, by which glycogen is deposited in that organ, is a provision 

 for the storage of the carbohydrates of the food ; otherwise the dex- 

 trose, after it had reached a percentage above that which normally 

 exists in the blood, 0.1 to 0.2 per cent., would be of no use to the 

 body, inasmuch as it would be eliminated by the kidneys. But, 

 being stored up in the liver at the time of its absorption, it is, in 

 the intervals of digestion, gradually converted into dextrose, which 

 passes out in the blood of the hepatic veins and serves the body 

 as a source of energy. It is a matter which is still in doubt 

 whether this conversion is a zymolytic action i. e., whether it 

 is produced by an enzyme or by the liver-cells as one of their 

 peculiar functions. The argument against the change being due 

 to an enzyme is, that while amylolytic enzymes have been found in 

 the liver, which change glycogen to maltose, here is a change 

 to dextrose ; but, on the other hand, a ferment has been obtained 

 from the liver which does convert glycogen into dextrose, so that 

 this argument has but little weight. That the power to change 

 glycogen into dextrose resides in tissues independently of the pres- 

 ence of enzymes is shown by the fact that the muscles of the 

 body, during the entire life of an individual, and other organs, 

 such as the placenta, during fetal life, have the same power as the 

 liver to form glycogen from the dextrose of the blood. While 

 Bernard's theory has been generally accepted by physiologists, 

 there are those who oppose it, and among these the most promi- 

 nent is Pavy. 



Theory of Pavy. Pavy regards the dextrose which Bernard and 

 others have found in the hepatic vein as due to a change brought 

 about by the action upon the glycogen of an enzyme formed in 

 the liver after death. His analyses of the blood of the ascending 

 vena cava, which carries the blood coming from the liver, show 

 no increase of sugar over the blood obtained from other portions 

 of the circulation, provided that it is examined before post-mortem 

 changes have set in. For this purpose he kills the animal by 

 a blow upon the head, and immediately withdraws the blood. 

 [According to this theory, during life the glycogen of the liver 

 * does not become converted into dextrose, but is a source of fat and 

 (of proteid. That fat is formed in th,e body in considerable amount 



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