346 Brown.—Studies in the Physiology of Parasitism. /. 
lethal principle in relation to the wall of the cells of susceptible tissue 
(a knowledge which obviously can be obtained only by indirect means) it is 
impossible to decide with complete certainty between the two hypotheses 
presented. Nevertheless from the following experiment the view that the 
two actions are brought about by the same substance is rendered the J more 
probable. 
In Section F it was shown that extracts which had not been completely 
deactivated by heat possessed lethal activity; and in Section G that both 
actions were stopped sharply when the extract was neutralized. If therefore 
the lethal and macerating substances are different, it is improbable that 
heat and percentage of alkali would affect both in the same degree. Killing 
of the cells should thus continue independently of the macerating action 
after a certain stage is reached, that is, when the permeability of the cell- 
wall has been sufficiently increased. Nevertheless it is found that if the 
macerating action is stopped, even at a very late stage, the killing effect is 
strongly retarded. 1 Such evidence is most readily interpreted according to 
the view that the lethal and macerating substances are identical. 
If we accept the hypothesis that lethal and macerating actions are due 
to the same substance, death of the cells is to be looked upon either as due 
to the direct action -of the macerating substance upon the protoplasmic 
membrane, or as the indirect result of the action upon the cell-wall, the 
phenomenon thus depending upon some special relationship between cell- 
wall and protoplasm. The former alternative predicates toxicity of the 
macerating substance; in the latter case death of the cells follows dis¬ 
integration of the cell-walls in a manner that is not understood. 
On the nature of the macerating substance little need be said. The 
present investigation bears out the conclusions of earlier workers that it is 
enzymic in nature. In the older literature it was known under the general 
name of ‘ cytase *; more lately it has been designated ‘ pectinase ’, from its 
1 It is impossible to stop the action of the extract by washing the partially disintegrated discs 
in water. The active principle remains adsorbed on the tissue, so that discs which have been taken 
from the active extract even at a comparatively early stage in the action and thoroughly washed in 
water are completely disintegrated in course of time. It is obvious, therefore, that no conclusions can 
be drawn from the behaviour of discs which have been taken from active extract and placed in extract 
which has been deactivated by heat. The only practicable method is to stop the macerating action 
by immersion of the discs in very dilute alkali (~~)> after which they are transferred to an extract 
which has been rendered exactly neutral. In experiments with discs of Swede Turnip, it was found that 
up to and a little beyond the stage termed ‘ coherence gone ’, the above treatment considerably delayed 
the incidence of death. As the cell-walls have by this time undergone considerable disintegration, 
they cannot be conceived to be impermeable to the lethal principle present in the neutralized extract. 
We should therefore expect that discs at this advanced stage would show the killing effects as 
rapidly in the neutralized as in the ordinary extract. This, however, is not the case. That the discs 
in the neutralized extract do show killing after a longer or shorter time (depending on the stage at 
which they were removed from the active, extract) is not surprising. It is probable that a certain 
amount of action on the protoplasmic membrane had already taken place when the discs were 
transferred to the neutralized extract. 
