Brown .- — Studies in the Physiology of Parasitism . IV. 491 
days’ age ; by M 2 , the medium in which the fungus has germinated and 
developed for two days, and so on. 
Experimental Method. 
In the case of thin sowings of spores, a quantity of the nutrient fluid 
(turnip extract) was infected in a flask with a small tuft of mycelium con- 
taining spores: for the thick sowings the method described in No. I of this 
series was adhered to. At the end of the period allowed for develop- 
ment, the nutrient medium was separated from the fungal mass by filtration 
through muslin. The fungal mass was thoroughly washed, dried, ground, 
and extracted in the manner already described. 
Spores sown thinly . The general nature of the results obtained is 
indicated in the following experiment : 
Three Erlenmeyer flasks, each containing 25 c.c. of turnip extract, were 
infected with a tuft of mycelium, and incubated at 20° C. Development 
in all three flasks appeared equal.. Flask A was tested after 1 week, 
B after 2 weeks, and C after 3 weeks, the M and H preparations (o*i grm. 
to 3 c.c. water in the case of the latter) being compared with standard 
extract. The activities of the various preparations are given in the following 
table, that of standard extract being taken as unity : 
A (1 week). B (2 weeks). C (3 weeks). 
h 7 m 7 h 14 . m 14 h 2J m 21 
o*2— 0*25 0*17 0*03-0*04 0-06 less than 0.02 trace (?) 
In the case of both sets of preparations, the activity is seen to diminish 
continuously after one week, and at the end of the third week it is reduced 
to a negligible quantity in both cases. The further consideration of the 
H preparations will be taken up later. In the case of the M preparations, 
seeing that initially the enzymic activity is nil, it is plain that activity 
increases with time to a maximum and subsequently declines. The nature 
of this relationship is shown more clearly by the following more detailed 
figures. The dry weight of hyphal material derived from each culture is 
added : 
Age in days 2 46 9 12 
Activity of M prep. <0*03 0*2 0*2 0*13 0*08 
Dry wt. of mycelium 0-017 grm. 0*27 0*36 0*33 0*37 
It will be observed that enzymic activity is slight on the second day ; 
that the maximal activity is reached in the neighbourhood of the fourth 
to sixth days ; also that about the latter time stagnation in the growth 
of the mycelium has been reached. 
L 1 
