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secreting cells “produce” a substance which remarkably resembles 
the blood-liquid and which therefore those cells hardly alter actively : 
osmotic pressure, concentration of the various salts and crystalloids 
and of the H-ions, they all oscillate within narrow limits round 
values which are practically those always indicated for the blood.’) 
When, however, one states that the secreting membrane actively 
checks erystalloids (fluorescin for the liquid of the eye-chamber, 
aceton and other substances in the cerebro-spinal fluid), then the 
researches, justifying these conclusions, are nearly always open to 
criticism both on account of the method used and or account of 
their varying results’). The fact that these liquids contain only 
traces of proteins and that ferments, immune bodies are practically 
absent from them, does not tell at all for an active, vital stopping. 
For every well-functioning dialysing-membrane, every ultra-filter will 
do this too. 
What follows here is the provisional brief communication *) of 
the results of an investigation to find an answer to the question: 
in how far can the said liquids be regarded as ultra-filtrates or, 
rather, as dialysates? For the name ultra-filtrate indicates a liquid 
which is pressed through by means of a super-pressure (in this case 
the pressure of the blood) and with which a not unimportant speed 
of circulation is supposed. Now it is very probable, especially for 
the liquid of the eye-chamber that under physiological conditions 
the movement of the liquid is very slow. When these liquids follow 
the fluctuations in the composition of the blood, this will be the 
consequence of a process, of diffusion for the greater part, and 
further of direct filtration; consequently in our view a combination 
of dialysis and ultra-filtration. In how far does the composition of 
these liquids correspond to what we must expect if the separating 
layer between the latter and the primary fluctuating liquid (blood) 
acts as a simple dialysing-membrane? We need not find complete 
similarity: for the liquid interacts not only with the blood, but also 
with the remaining surroundings (cerebral tissue, tissues round the 
eye-chamber). But it will be especially interesting to trace, which 
changes should be attributed to the last-mentioned factor. 
For the present we have limited our investigations to one of the 
substances which oceur normally in the blood, namely: glucose. 
1) See a.o. OSBORNE: Journ. of Physiology, 52, p. 347, 1918—1919. 
*) We hope to have an opportunity of returning to this question in further 
researches. 
5) A more elaborate publication will appear in the Biochemische Zeitschrift. 
