Brown.—Studies in the Physiology of Parasitism . L 327 
(v) The stability of the extract . The extract is not a stable solution, 
but loses its activity with lapse of time. After twenty-four hours in 
presence of chloroform, it has lost slightly in activity; after a week its 
activity is very small. The effect of this deactivation with time is to 
prolong the slow reactions unduly. This error can of course be corrected 
by renewal of the liquid from time to time. In the average experiment, 
lasting less than six hours, this procedure is not necessary, and the error 
introduced is not appreciable. 
Other Quantitative Methods. A variety of other methods has been tried 
from the point of view of a quantitative treatment of the subject. As these 
have been comparative failures, it is only proposed to mention them briefly. 
A substrate was prepared for the enzyme in the following manner. 
Turnip tissue was pulped, freed by prolonged washing from soluble 
materials, dried and ground to a powder. This may be considered to be in 
the main a cellulose powder. Water suspensions of this powder were added 
to the extract, and the action was estimated after a time by Fehling’s 
solution. This experiment was controlled by a similar one in which 
deactivated (see later) fungus extract was employed. The conclusion 
reached was that while the figures lay in the right direction, they were far 
too small to encourage the hope that the method might be serviceable. 
Quite apart from being very laborious, the method appeared infinitely 
inferior to the one adopted. The same remarks apply to a number of 
experiments in which an attempt was made to use as substrate a ‘ calcium 
pectate * extract of turnip tissue, prepared according to the method described 
by Behrens ( 1 . c.). 
In another series of experiments the killing action of the extract was 
followed by measuring the rate of escape of certain constituents of the 
tissue. Experiments along these lines were tried with tissues of turnip, 
onion, and beet. In the first two of these the action was estimated by 
Fehling’s solution, in the last it was measured colorimetrically. The con¬ 
clusion reached was that this represented a possible method which, given 
a suitable tissue, might furnish results of value. It did not appear, however, 
sufficiently promising to warrant its continuation at the time. 
An extensive investigation of plant pectins is at present being carried 
out in this laboratory by Dr. Schryver. It is hoped that on the basis of his 
results it may be possible to elaborate a suitable chemical method for stan¬ 
dardizing fungal extracts as regards their capacity to dissolve the cell-wall. 
is, however, quite unsafe, as there is no guarantee that the discs remain unaltered when so preserved. 
In point of fact, observations have shown that alterations do take place. Thus, if a number of discs 
from the same region of the same potato are preserved in different antiseptics, they are found after 
a week’s interval to show widely different degrees of sensitiveness to the action of the fungal extract. 
Variations amounting to as much as 400 per cent, have in this way been produced. A more striking 
example of the same phenomenon is given later (p. 344). The above serves to illustrate the dangers 
attendant upon this method of standardizing extracts. 
