Physiology. — “The Interchange between Blood-plasm on one hand 
and Humor aqueus and cerebro-spinal fluid on the other hand, 
studied from their sugar-percentages and in connection with 
the problem of combined sugar.” By J. pr Haan and S. van 
CreveLp. (Communicated by Prof. H. J. Hampurcer.) 
(Communicated at the meeting of March 26, 1921). 
Humor aqueus and cerebro-spinal fluid are two very remarkable 
tissue-liquids. They are so in the first place because they are almost 
entirely free from colloids and secondly because of the great simi- 
larity between their chemical composition and that of the blood. A 
large part of the present-day investigators are of opinion that these 
liquids must be regarded as formed by “active secretion” by certain 
layers of cells, namely the epithelial layer of the corpus ciliare and 
the chorioid plexus. HALLIBURTON and Dixon') a.o. have accepted 
this secretion especially for the cerebro-spinal liquid „on account of 
(among other things) the discongruity which would exist between 
the specific action of certain substances on the secretion of the liquid 
and the action of those substances on the pressure of the blood. It 
is, however, exceedingly difficult to establish experimentally and 
without any doubt, an increased formation of the liquid; and equally 
difficult is the exact determination of the blood-pressure in the 
vascular system, connected with the formation of the liquid. We 
here only refer to the recent elaborate publications of BecutT?) in 
which from his own researches this author reaches the conclusion 
that all the phenomena which at first sight point to secretion, may 
very well be explained in a mechanical way. For the rest we will 
leave out of consideration the significance of the blood-pressure, nor 
will we, in what follows, discuss the value of the argument that 
the histological gland-strueture of the said epithelial cells should 
furnish a proof for the secretion. Leaving elone the way the liquid 
is formed and the place where it originates, in other words leaving 
alone the direction of its movement, we wish to take as starting- 
point for our researches the chemical composition of these liquids. 
And then he who speaks of secretion here, will admit that the 
1) Journ. of Physiology 47, p. 215, 1913 and 48, p. 128, 1914. 
*) Americ. Journal of Physiology 51, 1, 1920. 
87 
Proceedings Royal Acad. Amsterdam. Vol. XXIII. 
