Brown . — Studies in the Physiology of Parasitism . IV. 493 
quantities of spores originally sown, the curve of activity obtained is 
of the same kind, but grades off more rapidly on both sides of the 
maximum. 
The material H x in these experiments is the same as the material 
employed for the preparation of standard extract (S). A comparison of 
H 0 , H. 3 , and H 6 with H x according to the method which has already been 
described showed the reduced activity of the extracts derived from these 
sources to be due to lack of enzyme and not to the presence of large 
quantities of retarding substances. 
Spores sown thickly — M preparations. The activities of the various 
M preparations corresponding to the H preparations just described are 
given in the following table, that of standard extract being taken as 
unity : 
M. 3 = trace M 4 = 1 M 2 = 1 M 4 = 0-87 M 6 = 0-25-0*3 
MjS' = 1 M 2 S' = 1 M 4 S' = 0-87 M 6 S' = 0-25-0-3 
M/S = 0-17 M/S = 0-2 M/S = 0-2 M/S = o-.i5 
It is seen from the above table that the activity of the M preparations 
passes through a maximum which is reached on the first to second day. 
The activity is very considerably reduced by the sixth day. 
A comparison of the figures in the second and third rows of the above 
table shows that the concentration of enzyme in M x , M 2 , and M 4 is much 
greater than in S ; and that the same applies in a less degree to M c . 
Nevertheless . the activity of M 6 is less than a third that of S. The pre- 
paration M 6 therefore illustrates the case of an enzymic solution in which 
the presence of a large quantity of enzyme is masked by the presence 
of retarding substances so that the full activity of standard extract is not 
reached. 
That the concentration of enzyme in S is relatively so small involves 
no contradiction, as a number of factors, such as degree of dilution, 
adsorption of enzyme on the fungal debris, loss on desiccation, might be 
expected to play a part in producing this result. 
The high concentration of enzyme in the M preparations is also shown 
in the following ways : 
1. While the activity of standard extract diminishes with dilution, that 
of such a preparation as M 2 remains unaltered up to a considerable degree 
of dilution. Thus by dilution to one-fourth the activity of S diminishes to 
a half (No. 1 of this series, p. 342), whereas dilution to one-eighth produces 
no appreciable diminution in the activity of M 2 . 
2. The M preparations are much less sensitive to the addition of salts 
and of plant extracts than is standard extract. The following table 
shows the retarding action of concentrations of KN 0 3 upon M 2 and standard 
extract : 
L 1 2 
