Measurements Em-ployed. 25 



ient position for the subject, who remained seated in his chair in the same 

 position as for the patellar reflex. The first and second fingers of the 

 right hand, immersed in a normal salt solution to the depth of 2 cm., 

 were used as receptors. The key in the primary circuit of the inducto- 

 rium was of the general type used by Martin, but operated by a small 

 motor at the regular rate of two breaks per second. Dodge had pre- 

 viously used a hand or foot control for breaking the primary circuit, 

 since the subject was in the room with the apparatus and the sound of 

 the regular Martin key gave secondary criteria when used in such 

 proximity. When the shocks are near threshold value, and particularly 

 if they are separated from each other by more than a second, the sub- 

 ject is apt to confuse them with the sensation from pulse beat, slight 

 finger movement, and changes of pressure. Furthermore, the attention 

 may be very unfavorable for observing the sensation at the actual time 

 of the shock. The regular, more rapid shocks produced by the me- 

 chanically operated key were substituted that they might supply more 

 favorable conditions and hence more consistent threshold values than 

 were produced by the previous method. Special photographic meas- 

 urements made with the aid of the string galvanometer across the sec- 

 ondary coil showed that two makes and breaks per second in the pri- 

 mary did not cause any decrement in the strength of the shock deliv- 

 ered by the secondary of the inductorium. In fact, there was no appre- 

 ciable decrement when the rate of make and break in the primary of 

 this coil was changed to 10 per second. The motor which operated the 

 key in the primary circuit was used always at the same speed, excepting 

 for changes brought about by the slight fluctuations in line voltage. 

 The make-shocks were not short-circuited from the fingers. They were 

 subthreshold, however, as the method employed (see Dodge and Bene- 

 dict's report, p. 135) was always to increase the stimulus strength of the 

 break-shock until the threshold was reached. The threshold value was 

 determined by averaging the first three ingoing threshold positions of 

 the coil. Three such average threshold values were determined, one 

 when the resistance in the circuit was simply that of the tissue and the 

 secondary coil, and the others with added resistances in the secondary 

 circuit of 20,000 and 40,000 ohms, respectively. From these three 

 values for Z, two j8 values were found according to the regular formula 

 of Martin. 1 The average of the two (3 values is the significant measure 

 for the period. Pulse record No. 3 followed the threshold measure- 

 ments. The subject had been sitting quietly for approximately 15 

 minutes previous to this pulse record. This condition favored relax- 

 ation. 



(4) Reaction time in reading isolated words. — The subject changed to 

 an ordinary chair and sat upright in front of an exposure apparatus 



1 Martin, Bigelow, and Wilbur, Am. Journ. Physiol., 1914, 33, p. 416; Dodge and Benedict's 

 report, p. 143. 



