35 
most colourless precipitate and that this is then gradually 
coloured a deeper and deeper blue. Of this Pfeffer 
makes no mention. 
On examination of the precipitate with reagents tannin 
reactions could be obtained, for example, the black colo- 
ration with ferric acetate. It may therefore be assumed 
that tannin is precipitated. The quantity of the precipitate 
even in Spirogyras with much tannin was however, small 
compared with other tannin precipitates. 
Hence I doubted whether the tannin is completely preci- 
pitated. After one day Î could not, indeed, demonstrate 
any tannin in the cell-sap in addition to the precipitate, 
but it seems that the cells may lose tannin by exosmosis. 
For when, for example, pieces of Spirogyra-filaments were 
placed in a dilute solution of methylene-blue, containing 
1/, /, gelatin, a precipitate was formed outside the cells 
and between the layers of the cell-wall which separated 
from each other. The precipitate was a compound of 
gelatin with tannin and became coloured black with ferric 
acetate. Î cannot therefore venture to assume with 
Pfeffer, that a complete precipitation of tannin takes 
place in the cell-sap. 
It seems to me that various factors play their part in 
the production of the precipitate. In the first place the 
harmful action of the methylene-blue, of causing great 
modifications in the organism. Further the presence of 
salts appear to assist the formation of precipitate. In a 
solution of one part of methylene-blue in 500.000 parts of 
distilled water the phenomenon was not so clear as in a 
solution of the same strength made with ditch-water or 
Knopp's fluid. À number of experiments in test tubes 
with methylene-blue, salts, gallnut- and Spirogyra-tannin 
led to the conclusion that the appearance of a precipitate 
is not only affected bij the presence of salts but that also 
atmospheric oxygen comes into play and finally, that me- 
Lo 
