Brown.—Studies in the Physiology of Parasitism, /. 335 
lamellae, and the whole structure becomes very fragile. This feature 
becomes more and more pronounced, and in course of time the tissue falls 
into a £ mush \ In no case has complete solution of the cell-wall been 
seen. Death of the cells takes place some time after fragmentation of 
the cell-walls is definitely established; the latter process, in the majority 
of cases examined, is not in evidence at a time when the tissue has lost all 
coherence as a result of the solution of the middle lamella. 
F. Examination of certain Physical Relationships of 
Extract. 
This investigation was undertaken in the first instance with the object 
of trying to effect a separation between the 4 macerating ’ and 4 lethal ’ 
principles of the extract. As the research proceeded it was, however, found 
expedient to develop it on broader lines. This examination in certain 
parts is not yet completed. 
Relation to Heating, 
The activity of the extract , both as regards macerating and lethal effects , 
is totally destroyed by a sufficient degree of heating . 
Below 55 0 C. deactivation is comparatively slow ; above this temperature 
it becomes very rapid, and at 65° it is as near as may be instantaneous. To 
study the effect of heating between the limits of 50° and 65°, the following 
method of heating was adopted by way of standard : 
A small tube containing 2 c.c. of extract was dipped into a beaker of 
water which was kept at a temperature 5 0 higher than the temperature 
desired. A thermometer served the double purpose of stirring the contents 
of the tube and recording the rise of temperature. The tube containing the 
extract was taken out immediately the required temperature was reached. 
This heating process, for temperatures between 50° and 65°, occupies 
approximately half a minute. 
The following table shows the rapid nature of heat deactivation when 
a temperature of about 55 0 is reached. The heating process was carried out 
in each case as described above. 
‘Macerating activity’ = reciprocal of time required to cause loss of coherence, that of unheated 
extract being taken as unity. 
Extracts tested on Turnip Discs . 
Treatment. 
Macerating 
activity. 
Heated to 
50 ° . . • 
. . . . 1 
53 ° • 
1 — 
55 ' ♦ 
§ 
y y 
58° . . . 
• • • • 7 
yy 
6o° 
1 
. . . . To 
yy 
63° • • . 
• • • • 
yy 
65° • • • 
0 
