give us indications of these conditions. A
complete cycle of molecular modifications can be traced, from the
abnormal negative to the normal positive, and then again to negative
seen in reversal under continuous stimulation.

FOOTNOTES:

[16] 'Considering that we have no previous evidence of any chemical or
physical change in tetanised nerve, it seems to me not worth while
pausing to deal with the criticism that it is not CO_2, but "something
else" that has given the result.'--Waller, _Animal Electricity_, p. 59.
That this phenomenon is nevertheless capable of physical explanation
will be shown presently.

[17] In order to explain the phenomena of electric response, some
physiologists assume that the negative response is due to a process of
dissimilation, or breakdown, and the positive to a process of
assimilation, or building up, of the tissue. The modified or positive
response in nerve is thus held to be due to assimilation; after
continuous stimulation, this process is supposed to be transformed into
one of dissimilation, with the attendant negative response.

How arbitrary and unnecessary such assumptions are will become evident,
when the abnormal and normal responses, and their transformation from
one to the other, are found repeated in all details in metals, where
there can be no question of the processes of assimilation or
dissimilation.

CHAPTER XV

INORGANIC RESPONSE--RELATION BETWEEN STIMULUS AND
RESPONSE--SUPERPOSITION OF STIMULI

Relation between stimulus and response--Magnetic analogue--Increase of
response with increasing Stimulus--Threshold of
response--Superposition of Stimuli--Hysteresis.

#Relation between stimulus and response.#--We have seen what extremely
uniform responses are given by tin, when the intensity of stimulus is
maintained constant. Hence it is obvious that these phenomena are not
accidental, but governed by definite laws. This fact becomes still more
evident when we discover how invariably response is increased by
increasing the intensity of stimulus.

Electrical response is due, as we have seen, to a molecular disturbance,
the stimulus causing a distortion from a position of equilibrium. In
dealing with the subject of the relation between the disturbing force
and the molecular effect it produces, it may be instructive to consider
certain analogous physical phenomena in which molecular deflections are
also produced by a distorting force.

#Magnetic analogue