Frog.  Reactions to  To 2d.   To 3d.  To 4th.  To 5th.  More.   Total No.
first Stimulus.                                    of Reactions.
1          53          2       1      0       0      1        57
2          20         12       5      5       4     12        58
4          31         15       1      0       2      8        57
5          51         11       1      2       0      1        66
6          45         15       6      3       1      5        75
Totals,   200         55      14     10       7     27       313

Table XI. is self-explanatory.  In addition to the usual averages, there is given the average for each half of the sets, in order that the effect of fatigue may be noted.  In general, for this series, the second half is in its average about one third longer than the first half.  There is, therefore, marked evidence of tiring.  The mean reaction time for this strength of stimulus is difficult to determine because of the extremely great variations.  At one time a subject may react immediately, with a time of not over a fifth of a second, and at another it may hesitate for as much as a second or two before reacting, thus giving a time of unusual length.  Just how many and which of these delayed responses should be included in a series for the obtaining of the mean reaction time to this particular stimulus is an extremely troublesome question.  It is evident that the mode should be considered in this case rather than the mean, or at least that the mean should be gotten by reference to the mode.  For example, although the reaction times for the one-cell stimulus vary all the way from 150[sigma] to 1000[sigma] or more, the great majority of them lie between 200[sigma] and 400[sigma].  The question is, how much deviation from the mode should be allowed?  Frequently the inclusion of a single long reaction will lengthen the mean by 10[sigma] or even 20[sigma].  What is meant by the modal condition and the deviation therefrom is illustrated by the accompanying curve of a series of reaction times for the electric stimulus of group I.

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100  110  120  130  140  150  160  170  180  190  200  210  220  230

The column of figures at the left indicates the number of reactions; that below the base line gives the reaction