990 
The second explanation, which has found many advocates, is that 
the blood sugar in the serum is not present in a free state, but is 
in normal circumstances only met with as a colloidal compound 
(LEPINE’s sucre virtuel), which cannot pass the glomerulus mem- 
brane. If the serum does not contain a quantity of this substance 
sufficient to bind the glucose, then part of the glucose remains 
circulating in a free state and can pass the glomerulus-epithelium, in 
other words glucosuria sets in. Several colloidal glucose compounds 
have been suggested already (jecorin, lecithin glucose, globulin-glucose). 
Objections have been raised, however, against this retention of 
sugar by a substance, present in the serum. Serum has been inade 
to dialyze against glucose-solutions (Asner, Rona and MrcHarus) 
and it was found that the percentage of glucose became equal on 
both sides of the membrane. A retention of sugar in a colloid form 
was, therefore, manifestly impossible. This statement has produced a 
considerable impression, and the result seems to be that matters 
have come to a dead stop. 
We have asked ourselves, however, if the results obtained in 
experiments with parchment membranes might be applied to glome- 
rulus epithelium. Obviously there is a possibility of compounds of 
glucose with some serumsubstance diffusing through a parchment 
membrane, but not through a membrane of glomerulus epithelium. 
BECHHOLD’s experiments have amply demonstrated that certain colloidal 
particles diffuse through one membrane, but not through another 
with smaller pores. 
We experimented, therefore, with celloidin membranes of various 
celloidin-percentages and ultrafiltrated under a pressure of 4 or 5 
atmospheres serum through it to which known quantities of glucose 
had been added, but the reduction-power of the ultrafiltrates did 
not warrant us to conclude that a colloidal glucose-compound had 
been kept back by the ultrafilter. 
Pursuing the same line of thought it seemed advisable now to 
investigate systematically whether in spite of the results of these 
diffusion- and ultrafiltration-experiments the second view was not 
the right one after all. 
In the first place it would have to be ascertained, which had 
not been done previously, that free glucose diffuses through the 
kidney. To investigate this, Rinerr-fluid, to which sugar had been 
added, would have to be transmitted through the vascular system 
of the kidney. If it was found then that the fluid flowing from the 
ureters contained the same concentration of sugar as the trans- 
mission-fluid, and if further it became evident that a RiINGER-fluid 
