34 
the growth of Spirogyra-filaments. In two cases this 
amounted in four days to 12 and 26!°/,;. I must here 
remark that Pfeffer has made no comparative experiments. 
If the rate of growth of Spirogyra cells in ditch water is 
studied, it is seen to be much greater. After two days 
the increase in length in 14 cases was found to be 25 to 
752/ and after four days in 18 other cases 40 40 7507 
From Pfeffer's results it is therefore clear that dilute 
solutions of methylene-blue also are harmful. 
My own experiments on Spirogyra maxima with me- 
thylene-blue (methylene-blue pro usu interno, the hydro- 
chloride), indicated that it was very harmful. In a solution 
of 1 part in 10000 parts of ditch-water all the cells 
perished in one day. In solution of 1 part in 500.000 
parts of ditchwater or Knopp's fluid many dead cells 
were seen after one day and in a solution prepared with 
distilled water of the same strength the number of dead 
cells was still greater. No growth was observed. The 
poisonous action of methylene-blue is the reason why 
there can be no question of ‘“Kontrole des jeweiligen 
Zustandes des Zellsaftes und der Veränderungen dieses im 
Laufe der Entwicklung'”, as Pfeffer imagines. 
It has been already demonstrated above that the cell-sap 
of Spirogyra contains no dissolved protein. The precipitate 
with methylene-blue cannot therefore as Pfeffer believes 
contain protein. In his opinion the precipitate is actually 
a compound of tannin with methylene-blue, which cannot 
be brought into agreement with the fact that solutions of 
methylene-blue, even stronger than those used by Pfeffer 
remain clear with solutions of gallnut- and Spirogyra- 
tannin. This is not explained by Pfeffer. 
It is noteworthy that when Spirogyra is placed in a 
dilute methylene-blue solution (1 in 500,000) there is no 
gradual formation of a precipitate which is coloured blue 
from the beginning, but there is first a colourless or al- 
