GENETIC TYPE AND THE ENDOCRINES 583 



difference in degree of reaction to the first shock is indicated 

 in column 3 of the table, one plus ( + ) sign indicating a more 

 extensive reaction to the shock with wider postural perform- 

 ance than a minus sign. 



Nature and course of the reaction. The course of the per- 

 formance also differed in the two groups. As a rule, the 

 dogs of group A developed a tolerance for the painful irrita- 

 tion and became less and less disturbed by it as the experi- 

 ments continued. Thus the value of the shock had to be 

 increased after the first few experimental periods. The animals 

 of group B never developed a tolerance to the shock and 

 continued to give vigorous general reactions until they learned 

 to avoid the shock. 



The sustained avoiding reaction of the foreleg to the con- 

 ditioning signal usually followed the appearance of a condi- 

 tioned flexion movement in which the leg was raised and 

 lowered alternately as the signal and shock continued. Since 

 the animal received a shock each time the leg was lowered, 

 the signal was automatically reinforced. All animals which 

 formed the conditioned flexion movement did so at about 

 the same stage of the training. The continued avoiding move- 

 ment, however, was not developed at the same time in all 

 animals, as is shown in columns 4 and 5 of table 7. In most 

 of the dogs of group B, the true avoiding reaction appeared 

 at about the time the conditioned flexion developed. The ex- 

 citatory value of the signal was so intense for these dogs, 

 and the association between the shock and the clicker so 

 well established, that the alternating reaction did not appear 

 as an integral of the pattern. 



The dogs of group A continued to give the alternating 

 reaction for a long period of time and never developed a 

 true sustained avoiding reaction. Furthermore, after the 

 experiments continued for a time, most of these dogs lost 

 the alternating response and only the actual shock would 

 elicit the flexion of the leg; the signal was entirely disre- 

 garded. This is shown in text-figure 101 (fig. 2). The reac- 

 tion to the shock was at this time a precise leg movement. 



