GENETIC TYPE AND THE ENDOCRINES 591 



different types of performance, with many intermediates 

 between the extremes. 



The dogs classified as group A are unable to make a true 

 continued avoiding adjustment. Some of them form the ' ' alter- 

 nating" or " pumping" reaction, that is, the dog raises and 

 lowers the leg while the signal sounds. This definitely indi- 

 cates the low excitatory value of the signal, since high ex- 

 citation would lead to definite (and sustained) contraction. 

 The inability of these dogs to make the avoiding adjustment 

 again emphasizes their lethargic nature and the tendency 

 to conserve energy. As in the salivary situation, they do 

 not react unless it is necessary. The behavior of these dogs 

 thus follows the same general pattern in the muscular per- 

 formance and in the less controlled glandular behavior. When 

 the signal is applied there is no perceptible increase in 

 breathing or heart rate. Neither the signal nor the shock 

 disturbs them. If the shock is increased beyond the liminal 

 point, they give a short bark as it is applied, but there is 

 no after-discharge of excitation and no further disturbance. 



The dogs classified as B are the excitable animals. They 

 formed the conditioned response readily, and it could be 

 elicited frequently without reinforcement. This is expressed 

 in terms of a high excitatory value for the signal. Even 

 after the avoiding response is made, the signal does not 

 lose its excitatory value. This is based not only on a delicate 

 balance or association between the auditory centers and the 

 neuro-muscular system of the leg, but also on a difference in 

 ratio between nervous excitation and inhibition in the nervous 

 system. An increase in the breathing rate is apparent when 

 the signal is applied. Some of the dogs whine or bark during 

 the signal, even though the painful irritation is avoided. 

 All these reactions indicate a greater degree of irradiation 

 of excitation throughout the correlated and associated reflex 

 systems than that found in the dogs of group A. If these 

 excitable dogs could not avoid the shock, they made violent 

 efforts to escape from the laboratory and soon developed 

 a nervous disturbance. This disturbance is evident bv the 



