440 
glycerine CH,OH’. CHOH . CH,OH 
erythrite CH;,0H .. CHOH? CHOH (CHO 
mannite CH:OH . (CHO), “CH/OH 
glucose CH.OH .(CHOH),. COH 
Injluence of substituted citrates on curdling by rennet. 
It seemed natural to begin the investigation with that bioche- 
mical or pharmacological process. the nature of which seemed mosi 
simple and by which the smallest number of complicating circum- 
stances might be expected. | 
To begin with, pharmacological actions may be excluded. For, 
an intravenously injected substance only acts after having been 
taken up by the tissues; the really acting concentration therefore 
is not only determined by the injected quantity (calculated pro kilo- 
gram of bodyweight) buc also by the partition-coéfficient tissue-blood, 
which is very different for different substances. 
The same difficulty complicates the investigation of immunity 
reactions; here also the  partition-coefficient_ leucocytes-serum or 
erythroeytes-serum varies considerably for various substances. 
Remains the coagulation of blood and milk-enrdling by rennet. 
Milkeurdling seems to be a so much simpler process than blood- 
curdling, the substances one has to work with, so much more 
stable, that milkeurdling seems to be the natural process to begin 
with. It is my intention to study later immunochemical and phar- 
macological processes with this method. 
In order to find the influence of citrates on the curdling of milk, 
I first observed how much the curdling-time was lengthened after 
addition of increased quantities of neutral citrate of sodium. I prepared 
a ‘/,, normal solution of sodiumeitrate, to which 2 drops of litmus- 
tincture were added and which by addition of a few drops of dilute 
hydrochloric acid or sodium hydroxide were brought to the same 
colour as distilled water with the same quantity of this indicator. 
1 40 normal solution obtained in this way, was diluted to an 1/80 
N, 1/100 N, 1/200 N, 1/500 N and 1/1000 N. I convinced myself 
that all these solutions remained neutral. 
In order to determine the curdling-time, 10 ce. of raw milk were 
pipetted into a test-tube, 2 ec. of distilled water, resp. a solution of 
citrate of different strength, were added, the test-tube was closed 
with a cork or a stopper of cotton-wool, well mixed and placed ina 
waterbath of 37° C. until it had reached this temperature. Then 
0.5 ec. of a solution of commercial rennet in distilled water (1 : 17) 
