THE METABOLISM OF THE CARBOHYDRATES 



691 



It will be observed that, so far as can be judged from changes in the concentration 

 of sugar in the blood, the sugar-retaining power of the liver is about equal to that of 

 the muscles. This result shows that the commonly held view is untenable that the liver 

 is capable of removing from the portal blood all of the sugar that is in excess of that 

 present in systemic blood. The muscles must assist extensively in this process. 



One objection which may properly be raised to these observations is that the animals 

 on which they were made were under anesthesia, and that the anesthetic may have had 

 a paralyzing effect on. the sugar-retaining power of the liver. In view of this criticism 

 it is important to examine the results obtained on animals that are not under the in- 

 fluence of anesthesia. Such observations have been made on rabbits, and a few on 

 man himself. By collecting blood from the ear veins of rabbits, it has been found 

 that, after giving from two to ten grams of glucose by stomach, the glucose concentra- 

 tion of the systemic blood begins to rise in fifteen minutes, attaining a maximum in 

 about an hour and then returning to the normal level in about three hours. 



Fig. 190. Curves showing the percentage of glucose in blood after a constant injection of 

 an 18 per cent solution into a mesenteric vein. V.C., vena cava, continuous line; P.O., pan- 

 creaticoduodenal vein, broken line; I, iliac, dotted line. 



Similar results have been obtained by examination of the venous blood 

 in man. After giving 100 grams of glucose by mouth, for example, there 

 is commonly an increase in blood sugar amounting to from 30 to 34 per 

 cent of the normal and lasting for from one to four hours. The existence 

 of this postprandial hyperglycemia, as we may call it, indicates that the 

 sugar-retaining powers of the liver and muscles are not sufficiently de- 

 veloped to prevent the accumulation of some of the absorbed sugar in the 

 systemic blood. Whenever this increase exceeds a certain limit, some of 

 the sugar begins to escape through the kidney into the urine, producing 

 glycosuria postprandial glycosuria. The concentration to which blood 

 sugar must rise before glycosuria occurs in the case of man is, probably 

 about 0.10 to 0.11 gm. per cent. After damage to the kidney, as in nephritis, 

 or in long-standing cases of mild diabetes, the percentage may probably 

 rise considerably higher in the blood without evidence of glycosuria. 



Value of Blood Examination in Diagnosis 6f Diabetes. The determina- 



