( 697 ) 
closely, in order to ascertain their value for the study of the phy¬ 
siological tannin problem. In doing this, special attention was directed 
to the following points: whether the substances penetrated rapidly 
into the cell and the cell sap, whether the tannin was completely 
precipitated, and what concentration of solutions was required for 
this; the nature of the precipitate and whether it redissolved on 
removal of the precipitant, whether the strength of the precipitate 
corresponded to the quantity of tannin in the cells and whether the 
method was sufficiently innocuous. After a number of experiments 
with antipyrine and caffeine solutions of various concentrations, 
which were allowed to act for a longer or shorter time, I came to 
the following conclusion: 
The antipyrine and caffeine solutions penetrate rapidly into the 
cells and in sufficient concentration produce in the cell sap a preci¬ 
pitate, consisting of minute grains or globules, which are in constant 
motion to and fro. In order to precipitate the tannin as completely 
as possible, it is desirable to have the antipyrine solutions not more 
dilute than 1 °/ 0 and caffeine solutions not weaker than */,, •/«• The 
greater the tannin content, the heavier the precipitate. Not infrequently 
the precipitate, is so heavy, that the nucleus, which ordinarily can 
be readily discerned in Spirogyra maxima, cannot be distinguished 
at all and sometimes the precipitate is even heavier. If the Spirogyra 
filaments are placed in ditch water or in distilled water, the preci¬ 
pitate disappears in a short time, say in 10 minutes, and the Spiro¬ 
gyra threads are as before the experiment. No change whatsoever 
can be detected. If the Spirogyra filaments remain in the solution, 
the precipitate settles down and the small globules or spheres, of 
which it consists, gradually coalesce to larger globules, which appear 
perfectly colourless and may sometimes be very large closely resem¬ 
bling fat globules. This was generally the appearance of the preci¬ 
pitate after a few days. The settling down of the precipitate in the 
cells and the fusion of the globules to larger, purely spherical masses, 
proves that it is heavier than water and that it is liquid. From several 
data I deduce that it is not. thinly liquid but viscid. The fusion to 
larger globules proceeds slowly and cannot, for instance, be brought 
about by a few minutes centrifuging. When the Spirogyra-cells with 
the globular precipitate are placed in water, the globules dissolve. 
Solution takes place more slowly, however, than in the case of a 
recently formed and still finely divided precipitate. If the preparations 
are placed in ferric chloride solution, instead of in water, the globules 
are coloured blue, while the cell sap is not coloured. It is rational to 
use caffeine as precipitant for this experiment, since antipyrine gives 
47 * 
