324 Brown.—Studies in the Physiology of Parasitism. I. 
this quantity of material is suspended in 21 to 24 c.c. water, furnishing after 
centrifuging 18 to 20 c.c. of extract. As the result of 26 days’ preparation 
of material, a maximum of 10 plates being employed, a quantity of 35 gr. 
of powder was collected. This represents a quantity of about 420 c.c. of 
standard extract. Again, as the result of 10 days’ preparation, about 
25 plates being sown daily, a stock of upwards of 60 gr. of powder 
was gathered, representing about 750 c.c. of extract. It is thus plain that 
the experimental treatment of this subject, according to the routine here 
adopted, offers no greater difficulties from the point of view of the availability 
of material than are met with in enzymic studies generally. 
In carrying out the above-described routine, no special precautions 
against bacterial contamination have been found necessary. Bacterial 
action would be considered most likely to show itself on the germination 
plates at the end of the germination period. No doubt bacteria do occur, 
though several examinations with the microscope have failed to demonstrate 
their presence. This state of affairs is probably to be set down partly to 
the acidity of the turnip medium, and partly to the vigorous development 
of the fungus spores. In any case a limited bacterial development is of no 
importance, as both bacteria and bacterial products are washed away in the 
further treatment of the fungal material. 
D. Quantitative Method of studying Action of Fungal 
Extract. 
The basis of the method is the capacity of the fungal extract to destroy 
the coherence of any susceptible tissue which is placed in it for a sufficiently 
long time. The method is as follows : 
From a tuber or other fleshy organ, an axial cylinder of about i-i| cm. 
diameter is cut by means of a cork-borer; this is cut across in the middle, 
and from the surfaces so exposed transverse sections of -§ mm. thickness are 
cut by means of a hand microtome. 1 The discs are now freed from con¬ 
tained air by injection under the pump with water. After thorough washing 
in distilled water, they are placed in the extract and the time noted that is 
required to bring about ‘ loss of coherence ’. For purposes of the present 
quantitative test, coherence is said to be lost , when the discs as tested by hand 
ojfer no perceptible resistance to a pulling stress . 2 The time from com¬ 
mencement of action to ‘ loss of coherence ’ gives a measure (inverse) of the 
activity of the extract. 
1 Leitz, Wetzlar. 
2 This stage does not represent the end-point of the macerating action even in its macroscopical 
aspects. The discs later become so fragile that it is impossible to handle them without rupture, 
though they do not actually fall asunder of their own accord. This stage, however, is difficult to 
determine, as there is no means of regulating or measuring the small strains which bring about 
rupture. 
