ng acids. I have
already shown how plants which previously gave strong response did not,
after application of an anaesthetic or poison, give any response at all.
In these cases it was the last stage only that could be observed. But it
appeared important to be able to trace the growing effect of
anaesthetisation or poisoning throughout the process. There were,
however, two conditions which it at first appeared difficult to meet.
First it was necessary to find a specimen which would normally exhibit
no fatigue, and give rise for a long time to a uniform series of
response. The immediate changes made in the response, in consequence of
the application of chemical reagents, could then be demonstrated in a
striking manner. And with a little trouble, specimens can be secured in
which perfect regularity of response is found. The record given in
fig. 16, obtained with a specimen of radish, shows how possible it is to
secure plants in which response is absolutely regular. I subjected this
to uniform stimulation at intervals of one minute, during half an hour,
without detecting the least variation in the responses. But it is of
course easier to find others in which the responses as a whole may be
taken as regular, though there may be slight rhythmic fluctuations. And
even in these cases the effect of reagents is too marked and sudden to
escape notice.

[Illustration: FIG. 43.--EFFECT OF CHLOROFORM ON NERVE RESPONSE (WALLER)]

For the obtaining of constant and strong response I found the best
materials to be carrot and radish, selected individuals from which gave
most satisfactory results. The carrots were at their best in August and
September, after which their sensitiveness rapidly declined. Later,
being obliged to seek for other specimens, I came upon radish, which
gave good results in the early part of November; but the setting-in of
the frost had a prejudicial effect on its responsiveness. Less perfect
than these, but still serviceable, are the leaf-stalks of turnip and
cauliflower. In these the successive responses as a whole may be
regarded as regular, though a curious alternation is sometimes noticed,
which, however, has a regularity of its own.

My second misgiving was as to whether the action of reagents would be
sufficiently rapid to display itself within the time limit of a
photographic record. This would of course depend in turn upon the
rapidity with which the tissues of the plant could absorb the reagent
and be af