336 Brown. — Studies in the Physiology of Parasitism . /. 
At and below 50° deactivation is relatively slow, as is shown by the 
following figures: 
Treatment. 
Heated at 50° for 15 min. 
Macerating 
activity. 
• • B 
» 5°° „ 45 min. 
. 
• • tV 
„ 45 0 „ 1 hour . 
. 
2 
• • ¥ 
,, 40° ,, 1 hour . 
. 
• • f 
„ 35 0 „ 1 hour . 
. 
. . I 
In all of the above cases where deactivation of the macerating principle 
was partial, it was seen that no separation of macerating and lethal 
principles had been effected. The lethal effect was tested in the case of 
the stronger solutions by injections into bean leaves; the weaker (much 
deactivated) extracts were tested as to their killing action on the more 
sensitive petals of Gloxinia. In all such cases a lethal action could be 
demonstrated. With extracts which had been completely deactivated in 
respect of their macerating action by heating to 65°, the lethal action was 
also completely stopped. This point is illustrated by the following ex¬ 
periment : 
Two discs of Crocus petal were injected under the air-pump, the one in 
unheated extract, the other in extract which had been heated to 65°. Both 
extracts had been previously cooled to nearly o° C., and throughout the 
experiment were kept in an ice chest. The disc injected with unheated 
extract was completely disorganized in an hour: that in the other was 
alive and apparently unaltered after five days, at which time, as bacteria 
were now beginning to appear in numbers, the experiment was discontinued. 
Throughout this work, extract which has been heated in the manner 
described to 65° has been used as the standard control. 
It is noticeable that heat deactivation causes a certain amount of 
coagulation in the extract, which is seen to become more opalescent. This, 
however, has nothing to do with the phenomenon of deactivation, as the 
extract when purified in certain ways shows the same sensitiveness to 
heating, but without exhibiting any coagulation. 
Relation to Mechanical Shaking. 
The extract may be deactivated by mechanical agitation—e. g. by 
bubbling air through it or by shaking in a closed vessel. As it is proposed 
to publish the results of this investigation separately, no detailed descrip¬ 
tion will be attempted here. The following figures illustrate the magnitude 
of the effect: 
(Agitation produced by a stream of bubbles.) 
Activity of extract maintained (but not shaken) at 35 0 for 1 hr. =1. 
„ „ „ shaken at 35 0 for | hr. =|. 
„ „ „ shaken at 35 0 for | hr. =|. 
