692 METABOLISM 



assimilation limit for sugar, which is often taken as an index of the sugar- 

 metabolizing power of the organism. It is evident, however, that the time 

 of onset, and the extent and duration of postprandial hyperglycemia must 

 serve as a more certain index of the efficiency of sugar metabolism. It 

 is now the usual practice to determine the sugar in samples of venous 

 blood removed immediately before and at half hour intervals following 

 the administration by mouth of 100 gm. glucose dissolved in water. This 

 is done on an empty stomach. In a healthy person the curve of blood 

 sugar rises within an hour to not above 0.15 per cent and the normal is 

 regained in two hours. In early diabetes the curve rises higher, stays 

 up for a longer time and does not return to normal for several hours. 

 Slight deviations from the normal must not be given too much weight in 

 diagnosis since they may occur in other diseases or even in perfectly 

 normal persons. 



In no disease, probably not even in tuberculosis, is it more important 

 than in diabetes that an early diagnosis should be made. Thus, if we find 

 that the postprandial hyperglycemia after a certain amount of carbo- 

 hydrate develops to an unusually high degree and persists for an unusual 

 length of time, we are justified in curtailing the carbohydrate supply so as 

 to hold these values down to the level they attain in normal individuals. 

 It is almost certain that the earliest sign of diabetes is an unusual degree 

 and duration of postprandial hyperglycemia. At first the excess of sugar 

 leads to no damage and it is insufficient to cause any evident glycosuria, al- 

 though it is quite likely that if the urine in such individuals were collected 

 at very frequent intervals after eating carbohydrate-rich food, glucose would 

 be found present in at least some of the specimens. In incipient diabetes, 

 however, the condition progresses, until the postprandial hyperglycemia 

 after one meal has not become entirely replaced before the next is taken, 

 so that the increase in sugar produced by the second meal becomes super- 

 added on that following the first meal. The curve of blood sugar rises 

 ever higher and higher, until at last permanent hyperglycemia is estab- 

 lished, or rather the normal level from which the postprandial rise occurs 

 has become permanently raised, so that in blood collected at any time a 

 higher percentage of sugar is found. 



The Relationship Between the Sugar Concentration of the Blood and 

 the Occurrence of Glycosuria. Claude Bernard first pointed out that the 

 percentage of sugar in the blood may rise considerably above its normal 

 level without the appearance of any of the sugar in the urine, or at least 

 without a sufficient amount appearing to give the usual tests for sugar. 

 Thus in man the blood sugar may rise to 0.17 per cent before sugar can 

 be detected in the urine. This has been called the renal threshold. Even 

 when the threshold has been overstepped, however, the sugar which 

 appears is not all of the excess but only a small part of it. 







