THE METABOLISM OP THE CARBOHYDRATES 655 



a sudden instead of a very gradual increase in the sugar concentration 

 of the blood, the conditions being quite unlike those which exist during 

 the normal absorption of glucose from the intestine. The mechanism 

 by which the body ordinarily disposes of excessive amounts of glucose 

 absorbed into the portal blood, is not adjusted to operate when the sys- 

 temic blood is suddenly overcharged' with this substance. In the one 

 case the glucose is a foodstuff; in the other, because of its excessive 

 concentration in the blood, it is more or less of a poison. Such results, in 

 other words, merely show us how much glucose can be added at one 

 time to the organism without any overflow into the urine, but they 

 furnish us with no information regarding the power of the organism to 

 utilize a constant though moderate excess of this substance. In the one 

 case it is the "saturation limit," in the other the "utilization limit" of 

 the organism for glucose, that we are really considering. 



Consideration of these principles has led Woodyatt, Sansum and Wil- 

 der 20 to undertake a thorough reinvestigation of the whole problem of 

 the utilization or, as they prefer to call it, the tolerance of the ~body for 

 glucose. They emphasize the obvious fact that the ability of the organism 

 to utilize glucose "must depend on the rate at which the tissues are 

 able to abstract it from the blood by their combined powers, to burn it, 

 to reduce it into fat or to polymerize it into glycogen. " To form any 

 estimate of the combined effect of these processes, we must take into 

 account not only the amount of glucose per unit of body weight (grams 

 per kilogram), but also the rate of injection, for "tolerance must be 

 regarded as a velocity, not as a weight." 



Briefly summarized, the conclusions which Woodyatt, etc., have so far 

 drawn from their investigations are as follows: In a normal rabbit, dog, 

 or man, 0.8-0.9 gm. of glucose per kilogram body weight and per hour can 

 be utilized by the organism for an indefinite time without causing gly- 

 cosuria. When between 0.8^ and 2 gm. are injected, a part of the excess 

 appears in the urine, steadily increasing until a maximum is reached, 

 after which the excreted fraction remains constant (at about one-tenth). 

 If more than about 2 grams per kilogram an hour are injected, "a large 

 percentage of all glucose in excess of the 2 gm. per kilogram an hour 

 appears in the urine when constant conditions are once established." 



The fact that so much glucose injected intravenously can be used 

 without the appearance of any of it in the urine, indicates a method by 

 which foodstuffs may be supplied to the tissues in cases where, on account 

 of gastrointestinal disturbances, it is impossible to have food absorbed 

 by the usual pathways. The possible value of such a method of treat- 

 ment in cases of extreme weakness has been tested on laboratory animals 

 by Allen, who states that such injection seems to have a valuable nutri- 



