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through the blood vessels of the kidneys a glucose solution which 
exceeds the physiological value (+ 0.07 °/,) only by about 0.03 °/,, 
already a little sugar is allowed to pass through, and, that this 
quantity increases according as the concentration of glucose becomes 
stronger, and that to the extent that with higher glucose concentrations 
less and less glucose is retained. The kidney cannot endure stronger 
glucose concentrations, 1.0. w. the glomerular membrane sickens. 
Towards galactose, however, the kidney behaved quite differently. Indif- 
ferent to whether stronger or weaker concentrations were used, a 
portion was always allowed to pass through, and what is remark- 
able, always about the half (see table | and II). The first explana- 
tion could therefore not be the correct one. 
Per exclusionem the second one had to be accepted then, namely 
this, that, of the two modifications in which glucose is present in 
aqueous solution, — the « and the 3 modifications, — the one is 
retained and the other is allowed to pass through. This conception 
agrees with the fact which we observed previously, ie. that the 
glomerular membrane is able to separate quantitatively from each other 
different sugars retaining one and letting pass through the other, which 
was demonstrated with mixtures of glucose and fructose, and glucose 
and lactose. The conjecture finds additional strong support in the fact 
that, according to our calculation, there are present practically equal 
quantities of the @ and 3 modifications in a solution of d-galactose, 
the same proportion thus, more or less, in which it is retained and 
not retained. For this very reason it cannot as yet be said with 
certainty, which modification is retained, the « or the 3. In the 
same position we are in the case of xylose, which like the d-galactose 
exhibits a partial retention. [t has appeared namely from our per- 
fusion experiments that on an average from */, to */, of the xylose 
is retained. « 
From the same point of view the partial retentions which were 
observed in connection with d-xylose, d-ribose and maltose may be 
looked at. Also these reducing sugars occur, in agreement with their 
multirotation, in two modifications; also these sugars exhibit partial 
retention. 
However it has appeared that not all sugars that occur in 
two modifications, show partial retention. In the first place the- 
d-glucose does not. If present in physiological concentration it is 
retained completely by the glomerular membrane, and as such it 
occupies a unique place; and still also the glucose occurs in two 
modifications. The latter applies also to l-glucose, d-mannose and |- 
and d-arabinose. Of these sugars nothing is retained. 
