Response in the Living and Non-Living | Page 8

cause is able to produce a particular molecular
rearrangement in the nerve; this constitutes the state of excitation and is
accompanied by local electrical changes as an ascertained physical
concomitant.'
'The excitatory state evoked by stimulus manifests itself in nerve fibres
by E.M. changes, and as far as our present knowledge goes by these
only. The conception of such an excitable living tissue as nerve implies
that of a molecular state which is in stable equilibrium. This
equilibrium can be readily upset by an external agency, the stimulus,
but the term "stable" expresses the fact that a change in any direction
must be succeeded by one of opposite character, this being the return of
the living structure to its previous state. Thus the electrical
manifestation of the excitatory state is one whose duration depends
upon the time during which the external agent is able to upset and
retain in a new poise the living equilibrium, and if this is extremely
brief, then the recoil of the tissue causes such manifestation to be itself

of very short duration.'--Text-book of Physiology, ed. by Schäfer,
ii. 453.
[4] I shall here mention briefly one complication that might arise from
regarding the current of injury as the current of reference, and
designating the response current either positive or negative in relation
to it. If this current of injury remained always invariable in
direction--that is to say, from the injured to the uninjured--there would
be no source of uncertainty. But it is often found, for example in the
retina, that the current of injury undergoes a reversal, or is reversed
from the beginning. That is to say, the direction is now from the
uninjured to the injured, instead of the opposite. Confusion is thus very
apt to arise. No such misunderstanding can however occur if we call the
current of response towards the more excited positive, and towards the
less excited negative.
[5] 'The Electrical Sign of Life.... An isolated muscle gives sign of life
by contracting when stimulated.... An ordinary nerve, normally
connected with its terminal organs, gives sign of life by means of
muscle, which by direct or reflex path is set in motion when the nerve
trunk is stimulated. But such nerve separated from its natural termini,
isolated from the rest of the organism, gives no sign of life when
excited, either in the shape of chemical or of thermic changes, and it is
only by means of an electrical change that we can ascertain whether or
no it is alive.... The most general and most delicate sign of life is then
the electrical response.'--Waller, in Brain, pp. 3 and 4. Spring 1900.
[6] Kunkel thought the electric disturbance to be due to movement of
water through the tissue. It will be shown that this explanation is
inadequate.
[7] My assistant Mr. J. Bull has rendered me very efficient help in these
experiments.
CHAPTER III
ELECTRIC RESPONSE IN PLANTS--METHOD OF NEGATIVE
VARIATION

Negative variation--Response recorder--Photographic
recorder--Compensator--Means of graduating intensity of
stimulus--Spring-tapper and torsional vibrator--Intensity of stimulus
dependent on amplitude of vibration--Effectiveness of stimulus
dependent on rapidity also.
I shall first proceed to show that an electric response is evoked in plants
under stimulation.[8]
In experiments for the exhibition of electric response it is preferable to
use a non-electrical form of stimulus, for there is then a certainty that
the observed response is entirely due to reaction from stimulus, and not,
as might be the case with electric stimulus, to mere escape of
stimulating current through the tissue. For this reason, the mechanical
form of stimulation is the most suitable.
I find that all parts of the living plant give electric response to a greater
or less extent. Some, however, give stronger response than others. In
favourable cases, we may have an E.M. variation as high as ·1 volt. It
must however be remembered that the response, being a function of
physiological activity of the plant, is liable to undergo changes at
different seasons of the year. Each plant has its particular season of
maximum responsiveness. The leaf-stalk of horse-chestnut, for example,
exhibits fairly strong response in spring and summer, but on the
approach of autumn it undergoes diminution. I give here a list of
specimens which will be found to exhibit fairly good response:
#Root.#--Carrot (Daucus Carota), radish (Raphanus sativus).
#Stem.#--Geranium (Pelargonium), vine (Vitis vinifera).
#Leaf-stalk.#--Horse-chestnut (Æsculus Hippocastanum), turnip
(Brassica Napus), cauliflower (Brassica oleracea), celery (Apium
graveolens), Eucharis lily (Eucharis amazonica).
#Flower-stalk.#--Arum lily (Richardia africana).
#Fruit.#--Egg-plant (Solanum Melongena).

#Negative variation.#--Taking the leaf-stalk of turnip we kill an area on
its surface, say B, by the application of a few drops of strong potash,
the area at A being left uninjured. A current is now observed to flow, in
the stalk, from the injured B to the uninjured A, as was found to be the
case