33 
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. Pfeffer !) has described this in 
detail. In particular he recommended methylene-blue 
which gradually produces a precipitate in the living cells 
of Spirogyra with a very dilute solution. 
In Pfeffer s*) opinion the tannin is completely precipit- 
ated 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 ex- 
planation which Pfeffer gives of the phenomenon he has 
observed is incorrect, whilst he greatly overestimates the 
value of the results obtainable by his method. 
Pfeffer *) writes: ‘‘In allen Fällen werden also Methylen- 
blau und andere Farbstoffe wertvolle Reagentien sein, mit 
deren Hülfe, ohne Schädigung, Aufschlüsse über Vorkom- 
men und Verteilung gewisser Kôrper in der Zelle zu er- 
halten sind. Mit solcher vielseitig ausnutzbaren 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.” 
Pfeffer frequently writes of the harmlessness of his 
method to life. As a proof of this he cites for instance 
1. 
2) rc "p: 183-and 216. 
te: jo ONE 
Recueil des trav. bot. Néerl. Vol. XI. 1914. 3 
