Early in the experiments it became evident that there were three clearly defined types of reactions:  there were a number of reactions whose time was shorter than that of the ordinary quick voluntary pain reaction, and there were also many whose time was considerably longer.  The first type it was thought might represent the spinal reflex reaction time.  For the purpose of determining whether the supposition was true, at the end of the series of experiments three of the frogs were killed and their reflex reaction time noted.  This was done by cutting the spinal cord just back of the medulla, placing the animal on an experimenting board close to the reaction key with the thread from the key fastened to the left leg as in case of the previous work and stimulating the gastrocnemius with an induced current by the application of wire electrodes.

In Table IX. the reflex reaction times for the three animals are given.

The following results obtained with frog E show that the time of reaction increases with the increase in the time after death.  The average of 20 reactions by E taken an hour after the cord had been cut was 45.5[sigma]; the average of 20 taken twenty hours later was 55.85[sigma].

As a rule the reflex reactions were but slightly variable in time as is indicated by the accompanying series.

SERIES OF REFLEX REACTIONS OF FROG F. 
Taken at rate of one per minute.

1                                50[sigma]
2                                58
3                                55
4                                59
5                                48
6                                46
7                                45
8                                51
9                                42
10                                44

Throughout these experiments it was noticed that any stimulus might cause (1) a twitch in the limb stimulated, or (2) a twitch followed by a jump, or (3) a sudden jump previous to which no twitch could be detected.  And it soon appeared that these types of reaction, as it seems proper to call them, would have to be considered in any determination of the mean reaction time.  As proof of the type theory there is given (Fig. 8) a graphic representation of 277 reactions to the electrical stimulus.

[Illustration:  FIG 8:  Distribution of 277 reactions.]

The column of figures at the left indicates the number of reactions at any point.  Below the base line are the classes.  For convenience of plotting the reactions have been grouped into classes which are separated by 25[sigma].  Class 1 includes all reactions between 1[sigma] and 25[sigma], class 2 all from 25[sigma] to 50[sigma], and so on to 400[sigma], thereafter the classes are separated by 100[sigma].  It is noticeable that there is one well-marked mode at 75[sigma].  A second mode occurs at 175[sigma].  This is the primary and in our present work the chiefly significant mode, since it is that of the quick instinctive reaction to a stimulus.  At 500[sigma] there is a third mode; but as such this has little meaning, since the reactions are usually pretty evenly distributed from 300[sigma] on to 2000[sigma]; if there is any grouping, however, it appears to be about 500[sigma] and 800[sigma].