494 Brow 7i. — Studies in the Physiology of Parasitism . IV. 
Concentrations <t/*KN 0 3 . 
n/ 00. 
11/128, 
»/ 3 2 * 
n/8. 
nj 2. 
M a 
1 
1 
0*87 
o *5 
o *33 . 
S 
1 
i(-) 
o *37 
0*08 
0-015-0*025 
A comparison of the M preparations in the case where the spores are 
thickly and where they are thinly sown is instructive : 
Manner of Sowing. Time in Days. 
012 4 6 9 12 
Thick o i i 0*87 0*25-0*3 — — 
Thin o — < 0-03 0*2 0*2 0.13 0*08 
The features of note are : 
1. In both cases the activity of the M preparations passes through 
a maximum. 
2. The effect of thick as compared with thin sowing is to increase the 
magnitude of the maximum, and to bring forward in time the date of its 
attainment. 
Effect of medium. Various media may be expected to give different 
quantitative results in view on the one hand of the retarding factors which 
they introduce, and on the other of the vigour of the growth to which they 
give rise. Only a few experiments have been carried out in this connexion. 
The various media employed were dilutions of a strong turnip extract. 
The following table gives the activities of the M preparations in the 
various media after twenty-four hours’ germination of the spores : 
T = turnip extract. 
in = a density of sowing equal to o*i c.c. spores in 10 c.c. nutrient. 
Density of Sowing. Nutrient . 
7 
T/10 
T/100 
7yiooo 
1)1 
1 
0*2 
0*1 
trace 
m/10 
0*2 
0*2 
0*1 
trace 
in / 100 
trace 
— 
trace 
trace 
in / 1000 
trace 
— 
trace 
trace ? 
The results of the above table can be summarized thus : The activity of 
the M preparation obtained is reduced both by diminishing the strength of 
the nutrient and the density of sowing of the spores. 
Further Comparisons between M Preparations and 
Standard Extract. 
1. Amount of retarding substances present. The amount of these 
substances present in standard extract (and extracts of mycelium generally) 
has been seen to be negligible (p. 490). The amount present in the 
M preparations, on the other hand, is considerable, being only somewhat 
