584 W. T. JAMES 



If the signal was continued, there might be a tendency to 

 hold the leg in the avoiding position for a brief time, but as 

 a rule alternate flexions and extensions of the leg were given. 



In contrast to this, note the brisk response of an animal 

 of group B in text-figure 101 (fig. 3). Although in this case 

 the leg was held high enough to avoid the shock, the record 

 shows movements of the leg while it is held in the avoiding 

 position. These are due to the shifting of the body as the 

 signal continued, which is superimposed on the avoiding 

 movement. It may be assumed, on the basis of physiological 

 experiments on muscular excitation, that excitation of a 

 greater frequency is required to produce the sustained and 

 continued avoidance than is required to produce the alter- 

 nating or incomplete tetanus reaction. On this basis it must 

 be concluded that the animals of group B are more excited 

 during the conditioning signal than are those of group A. 

 The greater irradiation of excitation is indicated by the 

 sudden increase in breathing and the postural changes which 

 accompany the avoiding reaction. 



Bead ion time. In addition to the differences in the de- 

 velopment and form of the reactions, there are differences in 

 the delay of the conditioned leg movement of the two groups 

 of dogs. Throughout the experiments the conditioning signal 

 preceded the shock for 5 seconds. In the animals of group 

 B, which formed the true avoiding behavior, the reaction 

 occurred shortly after the signal was introduced. The con- 

 ditioned reaction time was measured in seconds and fractions 

 of seconds by a Cornell chronoscope which is so arranged 

 that the timer starts when the signal is cut on and auto- 

 matically stops when the animal raises the leg. These read- 

 ings were made when the reaction had become well established, 

 and are not to be confused with reaction time in the usual 

 sense. In this case, it is the average latent period of the 

 conditioned avoiding movement to the signal which preceded 

 the shock. This time is shorter in the dogs of group B. 

 The readings are shown in column 6 of table 7. For example, 

 the Saluki had the shortest time, of .4(i seconds; that is. the 



