266 ROLLIN T. WOODYATT 



supply of food from exogenous sources ceases, the supply from the tissues 

 increases and that in a normal individual weighing 50 kg., 50 to 100 gm. 

 of glucose or more per day may be liberated in the body in the fasting 

 catabolism of glycogen, protein and the glycerol of fat. In experiments 

 of the above type the glucose administered passes first to trie liver at the 

 rate of absorption and probably emerges into the caval blood at a slower 

 rate. The effect on the rate of excretion through the kidneys will natur- 

 ally depend other things being equal on the rate at which glucose gains 

 access to the systemic blood. It will be noted that in the above experiments 

 doses of 34.5 gm. of glucose (per 50 kg.) caused the appearance in the 

 urine of about 2.8 gm. of sugar in excess of that for the control period, 

 i. e., about 8 per cent of the dose given was excreted (within 2 hours). 

 This is in the general neighborhood of the percentage excretions ob- 

 served by Sansum and Woodyatt when working with sustained intraven- 

 ous injections of glucose at rates of 1 to 2 gm. per kg. hour. Probably 

 then this dose of glucose by mouth led to the introduction of glucose into 

 the systemic blood at about the above average rate. The curve of glucose 

 excretion under higher rates of supply can not be followed far by the 

 administration of larger doses of glucose by mouth because the upper limit 

 for absorption rates is soon reached and the administration of more sugar 

 than merely prolongs the duration of absorption without driving the rate 

 above a certain maximum. However, when the rate of intravenous injec- 

 tion is accelerated, the rate of excretion rises absolutely and relatively. 

 With injection rates of 4.5 to 5.4 gm. per kg. hour sustained for several 

 hours, the excretion may rise in some dogs to 40 and 50 per cent of the, 

 quantity given and then remain virtually constant. Kleiner and Melzer, 

 making single massive injections, within a brief time (rate possibly 15 

 to 20 grams per kg. hour or more) saw as much as 70 per cent of the dose 

 excreted. Thus even in health it appears that there may be an absolute 

 limit of tolerance beyond which all glucose given escapes utilization. We 

 then have a curve consisting of a flat first portion which then bends rap- 

 idly upward and rises more and more steeply as the supply increases, some- 

 what after the manner of an exponential curve. A glycosuria might be 

 considered as abnormal when with a known normal supply it is greater 

 than with normal subjects under the same supply. 



Any supply of glucose up to the limit that can be produced in a nor- 

 mal subject by feeding might be considered as not beyond the normal pos- 

 sibilities. Any glycosuria therefore greater than that which can be pro- 

 duced in health by the feeding of glucose will probably always be abnormal 

 since it could only result (a) from a subnormal utilization; (b) an abnor- 

 mal supply from endogenous sources; or, (c) an anomaly of excretion. 

 But, of course, lower grades of glycosuria might also be abnormal if the 

 supply rate were lower. 



