It is obvious that in the water in which Spirogyra grows and also 
in the cell-sap salts are present and I have on this account traced 
the influence of various salts on the precipitation of gallnut- and 
Spirogyra-tannin by ammonium carbonate. I found that precipitation 
is favoured by salts; expecially is this the case with calcium salts. 
The formation of a precipitate in the cell-sap at greater dilution of 
ammonium carbonate is therefore readily explicable. 
Intravital precipitates can in many case also be brought about 
by aniline dyes. Prurrer *) has described this in detail. In parti- 
cular he recommended inethylene-blue which gradually produces a 
precipitate in the living cells of Spirogyra with a very dilute solution. 
In Prerrer’s © opinion the tannin is completely precipitated as 
a methylene-blue compound. The precipitate is also supposed to 
contain protein. When the solution of methylene-blue is sufficiently 
dilute, the precipitation is regarded as innocuous to the vital processes. 
The explanation which Prurrer gives of the phenomenon he has 
observed is incorrect, whilst he greatly overestimates the value of 
the results obtainable by his method. 
Prerrer ®) writes: “In allen Fallen werden also Methylenblau und an- 
dere Farbstoffe wertvolle Reagentien sein, mit deren Hülfe, ohne Schä- 
digung, Aufsehliisse über Vorkommen und Verteilung gewisser 
Körper in der Zelle zu erhalten sind. Mit solcher vielseitig ausnutz- 
baren Methode lässt sich unter richtiger Erwägung nach vielen 
Richtungen hin eine Kontrole des jeweiligen Zustandes des Zellsaftes 
und der Veränderungen dieses im Laufe der Entwicklung erreichen.” 
Prevrer frequently writes of the harmlessness of his method to 
life. As a proof of this he cites for instance the growth of Spirogyra- 
filaments. In two cases this amounted in four days to 12 and 
26°). 1 must here remark that Prerrer has made no compara- 
tive 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 te 75°/, and 
after four days in 18 other cases 40 to 75°/,. From Prerrer's 
results it is therefore clear that dilute solutions of methylene-blue 
also are harmful. 
My own experiments on Spirogyra maxima with methylene-blue 
(methylene-blue pro usu interno, the hydrochloride), indicated that 
it was very harmful. In a solution of 1 part in 10000 parts of 
‚p. 183 and 218. 
ape 
