GENETIC TYPE AND THE ENDOCEINES 745 



tions. The intellectual sluggishness and apathy of the human 

 cretin is proverbial. It would therefore be entirely unreason- 

 able to interpret the above facts to mean that the dog is capable 

 of better auditory discrimination under the condition of 

 thyroid deficiency than in the normal state. An increase in the 

 number of times the animal fails to respond to the negative 

 stimulus because of a subnormal condition cannot signify an 

 increase in discriminating and differentiating ability. 



According to the theory of Pavlov, these results may be 

 interpreted as showing a strengthening of the inhibitory 

 process to a point where inhibition is almost completely pre- 

 dominant over excitation. In this interpretation both excita- 

 tion and inhibition are viewed as dynamic processes. Ac- 

 cordingly, the diminution in the values of the positive C-R, 

 together with an increase in the number of negative reactions 

 following the operations, would mean that inhibition had 

 arisen from the deficiency in the gland secretions and was 

 thus predominant over excitation. Such a concept concerning 

 inhibition in the interpretation of these results is not only 

 unnecessary, but erroneous. We are concerned with an altera- 

 tion or lowering of the degree of excitation rather than with 

 a shift in the balance between the opposing forces of ex- 

 citation and inhibition viewed dynamically. 



The level of excitation varies inversely with the threshold 

 of stimulation; the higher the level of excitation, the lower 

 the threshold of stimulation and vice versa. The response to 

 a positive conditioned stimulus, and the response to a nega- 

 tive, differ not in kind but in degree. When the animal is 

 rendered ill or otherwise disturbed, the level of excitation 

 is lowered and both responses are less easy to arouse than 

 before. Thus we see that the positive and the negative re- 

 sponses have a constant relation to one another and to the 

 level of excitation. 



These animals, before operation, showed evidence of a rela- 

 tively high level of excitation. The positive conditioning 

 stimulus evoked a strong response in nearly every case, and 

 the negative stimulus in many cases evoked a response almost 



