Brown.—Studies in the Physiology of Parasitism. I. 343 
it was stated that extracts of greater concentration than the standard 
did not appear to possess any increased activity. This asymptotic effect 
suggests that some other limiting factor comes into play when the higher 
concentrations are reached. Such a factor may be the rate of diffusion 
of the active principle into the tissue of the discs experimented with. The 
above considerations also show how it is that in certain cases a better com¬ 
parison of the strengths of two extracts may be obtained by using the 
diluted in place of the extracts of full strength. 
Influence of Plant Juices on Activity of Extract. 
That plant juices retard the action of the fungal extract was known at 
an early stage of this investigation, and in fact this knowledge formed the 
starting-point of the experiments which have just been described. A series 
of experiments was now carried out to see if there is much difference among 
various plant juices in respect of the effect they produce upon the fungal 
extract; and more particularly, to see if any parallelism could be traced 
between the specific retarding effect of the plant extract and the relative 
immunity of the plant itself to the action of the fungus or of the fungal ex¬ 
tract. It was known that a high degree of resistance to the action of the 
extract was shown by tissues of mosses and hepatics; and it was therefore 
of considerable interest to determine if this want of activity of the fungal 
extract was due to its deactivation by some specific anti-body capable 
of extraction from the resistant tissue. 
The plant juices were prepared without dilution by squeezing through 
unsized filter cloth under high pressure. The crude turbid juice was cleared 
as far as possible by centrifuging before being used. The following table 
gives the figures obtained. 
By * concentration ^ 1 is meant that in each 1 c.c. of the liquid to 
which the figure refers there were yg- c.c. of plant juice and 1—5? c.c. of fungal 
extract; and so on. 
Column A = extract made by suspending o-2 gr. Botrytis powder 
in 3 c.c. plant juice. 
Plant. 
O 
Concentration of Plant Juice. 
111 1 
36 18 12 5 
1 
2 
A 
Remarks. 
Cotyledon rosacea (leaf) 
1 
I-t 
i-t 
i-f 
£ 
ir 
iV 
Clear. 
Bean (leaf). 
1 
I 
1 (-) 
i(-) 
Very variable. 
0 
0 
Turbid. 
Lemon (fruit) .... 
1 
h 
\ 
t 
i 
ira-iis 
< 4 TT 
Clear. Acidity = i*iN. 
Orange (fruit) .... 
1 
t 
t 
i 
f 
4 
Clear. Acidity = o*2 N. 
Potato (tuber) .... 
1 
i-f 
3 
4 
? 
J- 
Turbid. 
Fegatella (thallus) . . 
1 
i(-> 
i(-) 
i(-) 
3 
i 
b 
Turbid, mucilaginous. 
Cucumber (fruit, middle 
watery portion) . . 
1 
i(-) 
i(-) 
i(-) 
i-i 
2 f 
Slightly turbid. 
Cucumber (basalportion) 
1 
i(-) 
i(-) 
I (“) 
2 
•5 
i-f 
* 
Slightly turbid. 
Apple.. 
1 
i(-) 
i(-) 
i(-) 
1 
Clear. 
