84 Frederic Czapek . — The Anti-ferment Reaction in 
and it is possible to prepare by means of a certain temperature an effective 
specimen of toxin, from a mixture of toxin and anti-toxin, by destroying the 
anti-toxin. In the same way, heating for one hour to 6 2° entirely annuls 
the retardation in the disappearance of homogentisinic acid in a preparation 
of stimulated root-tips ; so that the reaction becomes identical with that 
observed in unstimulated root-tips. 
This result is interesting in still another point. The experiments 
show that preparations of unstimulated root-tips lose their oxydasic effects 
at a certain temperature without the occurrence of any acceleration of the 
oxydation of homogentisinic acid. Therefore it may be supposed that the 
anti-oxydase does not exist in unstimulated roots, but it is formed only by 
tropistic stimulation. 
Thus the interpretation of the process of metabolism in geotropic 
stimulation discovered by me is more exactly defined. It is essentially 
a retardation in the metabolism, in other words, in the decomposition of 
tyrosin. The tyrosin is, by tyrosinase, converted into homogentisinic acid, 
as occurs normally, but the further oxydation of the homogentisinic acid by 
the oxydase is inhibited by the production of an anti-oxydase, rendering the 
oxydase partially inefficient and causing by this means an accumulation of 
homogentisinic acid. 
This process may, for convenience sake, be called the ‘Anti-ferment 
Reaction.’ 
The exact investigation of the retardation of oxydation by the tropistic 
anti-enzyme is precisely suited to the application of chemical methods to 
the movement of plants, because the differences between stimulated and 
unstimulated organs can be magnified at will by the addition of homo- 
gentisinic acid, and can thus be completely removed from the doubts and 
uncertainties which interfere with the results of the direct titration method 
described in the earlier part of this paper. We thus obtain the very delicate 
and trustworthy method of chemically investigating the phenomena of 
irritability, which I proceed to describe. 
The root-tips to be analysed are ground as quickly as possible with 
glass-powder and water (io cc.), and are thus converted to a thin homo- 
geneous emulsion or mash. The mash is washed without loss into an Erlen- 
meyer flask of ^ litre capacity, and 5° cc. of standard aqueous solution 
of homogentisinic acid are then added. The titration of the acid used 
in my experiments gave io cc. as about equivalent to 2-3 cc. ~ AgN 0 3 . 
Finally, 5 cc. chloroform are added. The mixture is allowed to settle for 
ten to fifteen minutes, then 5 cc. are taken to determine the initial reducing 
power. The specimens now remain uncovered in an incubator (28 to 30°), 
and are shaken several times every day. At intervals of five days 5 cc. 
are taken to determine the reducing power. In such a way the decrease 
