688 METABOLISM 



furnish us with no information regarding the power of the organism to utilize a con- 

 stant though moderate excess of this substance. In the one case it is the ' ' satura- 

 tion limit, ' ' in the other the l ' utilization limit ' ' of the organism for glucose, that we 

 are really measuring. 



The Tolerance of the Body for Glucose. Consideration of these prin- 

 ciples has led Woodyatt, Sansum and Wilder 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 obvi- 

 ous fact that the ability of the organism to utilize glucose "must de- 

 pend 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- 

 tive and strengthening effect. He found, for example, that in cats 

 starved to extreme weakness the injection of a fraction of a gram per 

 kilogram of glucose had an unmistakable strengthening effect, and 

 sometimes appeared to save life. Such results would seem to indicate that 

 in certain cases where blood transfusion is impracticable, glucose in- 

 fusions should be tried. Subcutaneous injection of sugar, either for the 

 purpose of determining the assimilation limit or with the object of sup- 

 plying foodstuffs parenterally, is impracticable because of the pain and 

 sometimes sloughing produced at the point of injection. 



