638 DIABETES 



The immediate factors of greatest importance are the blood sugar 

 concentration and the area of kidney membrane exposed to the blood. 

 Even a casual observation of the kidney meiii1)rane as it appears in a 

 glomerulus with its capillary loops, capable of intlation and deflation 

 with varying volumes of blood, will show that the surface of contact 

 between the blood and the kidney membrane is subject to wide and 

 easy variations. If the blood sugar concentration remained constant 

 during sucli changes of the expanse of membrane in contact with the 

 blood these latter changes would obviously cause variation in tlie rate 

 at which sugar molecules entered the membrane from the blood. Or, 

 if the blood sugar percentage varied, the rate at which sugar mole- 

 cules entered the membrane as a whole might remain constant if the 

 membrane varied its expanse in direct proportion to the blood volume 

 and in inverse proportion to the blood sugar concentration.^ It is 

 therefore apparent that observations of variations of the blood sugar 

 concentration can not afford a reliable index of the varying rates at 

 Avhicli sugar enters the kidney membrane, unless the blood volume, or 

 more exactly the surface of contact between the blood and cells, is 

 taken into account and the same principles apply in the case of all 

 tissues in general. Thus Epstein ^ observed that the total sugar of 

 the blood is a better criterion of the rate of glycosuria in diabetes 

 than the blood sugar percentage. The more remote factors which 

 determine the quantity of sugar brought to the kidneys via the blood 

 are the supply of sugar to and the utilization of sugar in the rest of 

 the organs of the body apart from the kidneys. 



The Utilization of Sugar may be considered for present purposes as 

 the sum of the ])rocesses by which a sugar such as glucose is converted 

 into something else within the cells. In the case of glucose it includes 

 oxidation to yield finally CO, and water; poJ)jnierization to yield a 

 series of substances, chief of Avhich is glycogen ; reduction to fat ; 

 transformation, as to lactic acid; comhination, etc. The rate of util- 

 ization " by all of these methods taken collectively is influenced in the 

 first place by the rate at which glucose molecules enter the cell and 

 secondly by the reaction conditions encountered within it. The 

 utilization rises with an increasing supply of glucose. As to the fac- 

 tors which enter into what we have called tlie reaction conditions 

 found within the cell there is little definite knowledge. With a con- 

 stant glucose sui)j)ly the rate of utilization may fall as the result of a 



* This brings up tlio question of the froonietrical forms of eapillaries. It is 

 interesting to recall tliat if a hollow cylinder donbles in length it doubles its 

 volume and also its lateral surface. Tliis tyjic of cajiiilary distension WMuld 

 fulfill tlie above conditions and other methods readilv suggest themselves. 



■•Jour. Biol. Chem., 1014 (IS), 21: Proc. Roc. Exp. Biol.. lOlC (1.3), 67: also 

 "Studies in Ilvperglvcemia in Relation to Clvcosuria," Albert A. Epstein, X. Y., 

 1910. 



It miglit not seem desirabh' (n iiichidc sucli processes as temporary storage 

 in the form of glycogen uiidcr llic licadiiig i)f utilization. Tlie term is used for 

 convenience. 



