CHAPTER X 

 ( METABOLISM, NUTRITION AND DIETETICS ) 



WE return now to the products of digestion as they are absorbed 

 from the alimentary canal, and, still assuming a typical diet con- 

 taining carbo-hydrates, fats, and proteins, we have to ask, What 

 is the fate of each of these classes of proximate principles in the 

 body ? what does each contribute to the ensemble of vital activity ? 

 It will be best, first of all, to give to these questions what roughly 

 qualitative answer is possible, then to look at metabolism in its 

 quantitative relations, and lastly to focus our information upon 

 some of the practical problems of dietetics. 



SECTION I. {METABOLISM OF CARBO-HYDRATES GLYCOGEN.^ 



(The carbo-hydrates of the food, passing into the blood of the 

 portal vein in the form of dextrose, are in part arrested in the liver, 

 and stored up as glycogen in the hepatic cells, to be gradually given 

 out again as sugar in the intervals of digestion. The proof of this 

 statement is as follows : 



Sugar is arrested in the liver, for during digestion, especially of a 

 meal rich in carbo-hydrates, the blood of the portal contains more 

 sugar than that of the hepatic vein. Popielski, on the basis of 

 experiments in which he fed with known quantities of sugar dogs 

 whose inferior vena cava and portal vein had been united by an 

 Eck's fistula, and determined the amount of sugar which passed 

 into the urine, estimates the quantity of sugar kept back by the 

 liver at from 12 to 20 per cent, of the whole. In the liver there 

 exists a store of sugar-producing material from which sugar is 

 gradually given off to the blood, for in the intervals of digestion the 

 blood of the hepatic veins contains more dextrose (2 parts per 1,000) 

 than the mixed blood of the body or than that of the portal vein 

 (about i part per 1,000). When the circulation through the liver 

 is cut off in the goose, the blood rapidly becomes free, or nearly free, 

 from sugar (Minkowski). And a similar result follows such inter- 

 ference with the hepatic circulation as is caused by the ligation of 

 the three chief arteries of the intestine in the dog, even when the 



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