11 7 
On the Physiology of Parasitism. 
permeability of the cell wall has been sufficiently increased. 
Nevertheless it was found that if the macerating action was stopped 
(by addition of the requisite amount of alkali), even at a very late 
stage, the killing effect is strongly retarded. Such an experimental 
result is not favourable to the present hypothesis. 
(4) That both actions are due to the same substance or group of 
substances. This view appears to the writer to be the simplest, and 
so far as is known, is in agreement with all the experimental facts. 
While hypotheses (1) and (2) are in the mind of the writer 
definitely excluded, a final decision between (3) and (4) cannot 
at present be given. From the point of view of the progress 
of the present investigation the question at issue is not of 
primary importance, as it is sufficient for present purposes that 
the lethal action of the extract has been shown to be indis¬ 
solubly connected with its macerating action. On theoretical 
grounds, however, this question is of very considerable moment. 
If the last-mentioned hypothesis be confirmed it would appear 
that we have in the active principle of the fungal extract a 
protoplasmic toxin which is presumably of an enzymic (i.e., hydroly¬ 
tic) nature. It is known that the active principle under consideration 
shows considerable specificity in regard to its behaviour towards 
cell wall constituents (cell walls of different plants, different 
constituents of the same cell wall). If such a behaviour could be 
shown in the case of the corresponding protoplasmic membranes, a 
practicable study of protoplasmic specificity could be undertaken. 
The main obstacle to such a study is one of technique. It would 
be essential to study the action of the extract upon the protoplasmic 
membrane independently of previous action on the surrounding cell 
wall, that is it would be necessary to experiment with protoplasts 
which are naturally naked or with ones which have been made so 
artificially. As the latter would probably furnish the data of chief 
interest, the technical difficulties in the way of this investigation are 
obvious. 
Conclusions on the nature of the Funoal Extract. 
Whichever hypothesis be accepted as explaining the lethal 
action of the extract, it is clear in any case that the chemical 
nature of the cell wall is of fundamental importance in relation to 
the action of the fungal extract upon the cell. In all cases it has 
been found that if the cell wall is disintegrated, death of the cell 
ensues ; if the cell wall is not affected, neither are the living contents 
