60 cm. long and 45 cm. deep.  On the bottom of this, at one end, a series of interrupted circuits were arranged as shown in the figure.  The wires were 1.2 cm. apart, and an animal sitting anywhere on the series necessarily touched two or more, so that when the stimulus key, X, was closed the circuit was completed by the animal’s body; hence, a stimulus resulted.  The stimulus key, X, was a simple device by which the chronoscope circuit, c, c, was broken at the instant the stimulus circuit, s, c, was made.

Cells of ‘The 1900 Dry Battery’ furnished the current used as a stimulus.  Three different strengths of stimulus whose relative values were 1, 2 and 4, were employed in the series 1, 2 and 3.  Careful measurement by means of one of Weston’s direct-reading voltmeters gave the following values:  1 cell, 0.2 to 0.5 volt, 0.00001 to 0.00003 ampere.  This was used as the stimulus for series 1. 2 cells, 0.5 to 1.0 volt, 0.00003 to 0.00006 ampere.  This was used for series 2. 4 cells, 1.2 to 1.8 volt, 0.00007 to 0.0001 ampere.  This was used for series 3.

[Illustration:  Fig. 9.  Ground Plan of Reaction Box for Electrical Stimuli (Group 2). IC, interrupted circuits; CC, chronoscope circuit; X, key for making stimulus circuit and breaking chronoscope circuit; B, stimulus battery; S, string from reaction key to animal.  Scale 1/2.]

The reactions now under consideration were taken in sets of 24 in order to furnish evidence on the problem of fatigue.  The stimulus was given at intervals of one minute, and the subject was moistened at intervals of ten minutes.  To obtain 24 satisfactory reactions it was usually necessary to give from thirty to forty stimulations.  Five animals, numbers 1, 2, 4, 5, and 6, served as subjects.  They were green frogs whose size and sex were as follows: 

Length.   Weight.      Sex. 
Number 1   7.5 cm.  35 grams.   Male. 
Number 2   7.3  "   37   "     Male. 
Number 4   8.2  "   50.4 "     Female? 
Number 5   7.1  "   25   "     Female. 
Number 6   7.8  "   42   "     Male.

For most of these frogs a one-cell stimulus was near the threshold, and consequently the reaction time is extremely variable.  In Table X. an analysis of the reactions according to the number of repetitions of the stimulus requisite for a motor reaction has been made.  Numbers 1 and 5 it will be noticed reacted most frequently to the first stimulus, and for them 48 satisfactory records were obtained; but in case of the others there were fewer responses to the first stimulus, and in the tabulation of series 1 (Table XI.) averages are given for less than the regular sets of 24 reactions each.

TABLE X.

  ANALYSIS OF REACTIONS TO ONE-CELL STIMULUS.