29 
contains so much acid that protein and tannin should be 
able to appear together in soluble form in the cell-sap. 
The experiments which I am about to describe, also show 
that Pfeffer has incorrectly interpreted his observations. 
Whilst with many reagents it is quite easy to demonstrate 
tannin in the cell-sap of Spirogyra because the cell-wall 
and protoplasm are permeable to these reagents, the most 
important tannin-reagents, namely, those which belong 
to the protein group cannot permeate. For this reason 
J heated Spirogyra in egg-white-, gelatin- or glue-solutions. 
On the death of the protoplasts the tannin passes through 
the protoplasmic layer and the cell-wall and a precipitate 
is formed outside' the cell. If, instead of allowing the 
tannin to pass out, a little protein solution could be intro- 
duced into the cell-sap which contains the tannin and if 
we could investigate the result, this would go a long way 
in my opinion towards solving the problem of whether 
in the cell-sap protein exists in solution as well as tannin. 
Should the cell-sap remain clear, one might be able to 
assume that the cell-sap was of such composition as to 
contain dissolved tannin and protein side by side. If, on 
the other hand, a small amount of protein-solution produced 
a precipitate, then this might be taken to exclude the 
simultaneous presence of the two substances. 
I will proceed to explain how I succeeded in introducing 
a protein-solution into the cell-sap, causing a precipitate 
which on closer investigation was found to be a compound 
of tannin and protein. 
As ÎI!) have previously described, the cytoplasm in 
Spirogyra possesses an alveolar structure. The hyaloplasm 
forms the walls of the alveoli, which are filled with a 
watery solution. By the action of reagents the structure 
1) C. van Wisselingh, Zur Physiologie der Spirogyrazelle. Beitr. 
zum Botan. Centralblatt. Bd. XXIV (1908). Abt. I. S. 190 f. 
