equal variability at some point)—­and our studies seem to show it for touch and electrical stimulation—­which I feel justified in offering at present, is that parity in variability indicates equality in strength of stimuli, that is, the electrical stimulus which has a reaction time of the same variability as a tactual stimulus has the same effect upon the peripheral nervous system as the tactual, it produces the same amplitude and perhaps the same form of wave, but the reaction times for the two stimuli differ because of the biological significance of the stimuli.  The chances are that this is wholly dependent upon the central nervous system.

IX.  SUMMARY.

1.  This paper gives the results of some experiments on the frog to determine its electrical and tactual reaction time.  It is the beginning of comparative reaction-time studies by which it is hoped important information may be gained concerning the significance and modes of action of the nervous system.  Comparative physiology has already made clear that the time relations of neural processes deserve careful study.

2.  According to the strength of the stimulus, electric stimulation of the frog causes three types of reaction:  (1) A very weak or threshold stimulus results in a deliberate or delayed reaction, the time of which may be anywhere from 300[sigma] (thousandths of a second) to 2,000[sigma]. (2) A very strong stimulus causes a spinal reflex, whose time is from 50 to 80[sigma]; and (3) a stimulus of intermediate strength causes a quick instinctive reaction of from 150 to 170[sigma] in duration.

3.  The reaction time for electric stimuli whose relative values were 1, 2 and 4 were found to be 300.9[sigma], 231.5[sigma] and 103.1[sigma].

4.  The reaction time of the frog to a tactual stimulus (contact of a rubber point) is about 200[sigma].

5.  The variability of reaction times of the frog is great, and increases as the strength of the stimulus decreases.

6.  When two kinds of stimuli (e.g., electrical and tactual) give reaction times of equal variability, I consider them directly comparable.

7.  According to this criterion of comparability the reaction time to electric stimulation which is comparable with that to tactual is 172.1[sigma]; and it is to be compared with 205.7[sigma].  Both of these have a variability of approximately 34[sigma].  On this basis one may say that the tactual reaction time is considerably longer than the electrical.

PART III.  AUDITORY REACTIONS OF FROGS.

X. HEARING IN THE FROG.

A. Influences of Sounds in the Laboratory.