As has been mentioned in connection with the discussion of fatigue, it was found absolutely necessary to have the subjects perfectly fresh and active, and for this purpose it was advisable to give not more than three or four stimulations at any one time.  The subject was usually kept in the reaction box from 30 to 45 minutes, dependent upon the success of the experiments.  As the work progressed it became evident that the responses to the stimulus were becoming less and less certain and slower, that the subjects were becoming accustomed to the novel experience and no longer suffered the surprise which had been the cause of the prompt reactions at first.  It seemed best for this reason not to continue the work longer than two weeks, and as a consequence it was impossible to base the averages on more than twenty reactions for each subject.

So far as the tension of the thread is concerned, the condition for the tactual reaction time was the same as that for the first group of electrical reaction-time experiments.  In comparing the tactual with the electrical of series 1, 2 and 3, allowance must be made for the slack in the latter cases.

Selection of the tactual reaction times upon which the mean is based, has been made with reference to the mode for each set of experiments.  Inspection of the curves given by the reactions of each subject indicated that the great majority of the responses lay between 100 and 300[sigma], and that those which were beyond these limits were isolated and, in all probability, exceptional reactions due to some undetected variation in conditions which should throw them out of the regular series.  On this account it was thought best to use only reactions between 100 and 300[sigma].

For convenience of comparison, again, the averages for the electrical reaction time of subjects A, B, C, D, E and F, and the same for the tactual reaction time of subjects 1, 2, 3, 4, 5 and 6 are herewith given together.  All averages are for twenty reactions, except for D and 5, for which there are ten.

Besides the usual determination for the tactual reaction-time work on the six subjects named, there is given in Table XVI. the electrical reaction time of these animals to a two-cell current.  Comparison of the electrical and tactual results are of interest in this case because the mean variation for each is about 34[sigma], being 34.3[sigma], for the electrical and 33.8[sigma], for the tactual.

TABLE XV.

Average of 20 Electrical           Average of 20 Tactual
Frog.           Reactions.           Frog.           Reactions.
A           149.5[sigma]       1               188.3[sigma]
B           158.3              2               199.1
C           191.0              3               212.1
D           167.0              4               213.0
E           182.4              5               199.8
F           176.3              6               221.9
Gen. Avs.       167.9                              205.7

TABLE XVI.