to an animal forces an immediate response so long as
the muscular system is not exhausted; but where, as
in series 1 and 2 of the electrical stimulus, the
stimulus is not harmful, the reason for a sudden reaction
is lacking unless fear enters as an additional cause.
Just as long as an animal is fresh and unfamiliar with
the stimulus there is a quick reaction to any stimulus
above the threshold, and as soon as a few experiences
have destroyed this freshness and taught the subject
that there is no immediate danger the response becomes
deliberate. In other words, there is a gradual
transition from the flash-like instinctive reaction,
which is of vast importance in the life of such an
animal as the frog, to the volitional and summation
responses. The threshold electrical stimulus does
not force reactions; it is a request for action rather
than a demand, and the subject, although startled
at first, soon becomes accustomed to the experience
and responds, if at all, in a very leisurely fashion.
The reaction time to tactual stimuli, soon to be considered,
was determined by giving a subject only three or four
stimulations a day; if more were given the responses
failed except on repetition or pressure; for this
reason the data on fatigue, or lengthening of reaction
time toward the end of a series, are wanting in touch.
A few tests for the purpose of discovering whether
the time would lengthen in a series were made with
results very similar to those of the threshold electrical
stimulus; the chief difference lies in the fact that
the responses to touch fail altogether much sooner
than do those to the electrical stimulus. This,
however, is explicable on the ground that the latter
is a stimulus to which the animal would not be likely
to become accustomed so soon as to the tactual.
First Half. Second Half. Second % Greater.
Series 1 244.8[sigma] 356.8[sigma] 46 per cent
Series 2 216.6 246.6 14 "
Series 3 101.0 105.9 5 "
If pure fatigue, that is, the exhaustion of the nervous
or muscular system, appears anywhere in this work,
it is doubtless in series 3, for there we have a stimulus
which is so strong as to force response on penalty
of death; the reaction is necessarily the shortest
possible, and, as a matter of fact, the motor reaction
(jump forward) here occupies little more time than
the leg-jerk of a decapitated frog. This probably
indicates that the reaction is a reflex, and that
the slight increase in its length over that of the
spinal reflex is due to occasional cerebellar origin;
but of this there can be no certainly from the evidence
herewith presented. At any rate, there is no
possibility of a voluntary reaction to the strong current,
and any changes in the general character of the reaction
time in a series will have to be attributed to fatigue
of the nervous or muscular systems. The second
halves of the sets of series 3 are 5 per cent. longer