744 O. D. ANDERSON 



and negative signals. This stimulus was used, however, in 

 three dogs following the administration of anterior pituitary, 

 parathyroid and thyroid extracts, respectively. Both thyroid 

 and parathyroid extracts were given to two dogs while an- 

 terior pituitary material was given to only one dog. The 

 constancy of the negative C-R increased following the para- 

 thyroid and thyroid substance by averages of 32 per cent and 

 11 per cent, respectively, and it decreased 33 per cent during 

 the administration of the anterior lobe extract to the one 

 animal. 



As the constancy and the magnitude of the positive C-R 

 decrease following the ablations, the constancy of the negative 

 C-R increases. There were occasions in the post-operative 

 periods when the positive Met. 120 served to evoke a weak 

 positive response, and during the same time the negative 

 Met. 28 gave no response at all. According to the usually 

 accepted criterion of differentiation in conditioned reflex 

 experiments, this record would constitute a differentiation. 

 It w r ill be recalled that with one post-operative dog, 864, the 

 negative metronome rate was advanced on successive days 

 to 42, to 60 and to 78 beats per minute. The Met. 120 evoked 

 the reflex response and the other rates did not. The response 

 appeared when the negative rate was advanced to 96. This 

 observation was on a dog after thyroidectomy. Before the 

 operation, this dog, during 8 months of differential tests 

 (Met. 120 against Met. 28), gave no evidence whatever of 

 distinguishing between the two rates. In the same way, after 

 thyroidectomy, thyro-parathyroidectomy, complete hypophys- 

 ectomy, castration, and ovariectomy, there was evidence of 

 discrimination between the positive and negative stimuli, 

 which was better after the operation than before. Little is 

 known, from either clinical or experimental observation, con- 

 cerning the relation of the parathyroids, the pituitary, the 

 testes and the ovaries to the higher nervous activities (mental 

 processes) in the human subject or the lower animals. But a 

 great mass of information has been collected concerning the 

 retardation of the psychical processes in hypothyroid condi- 



