674 O. D. ANDERSON 



C-R during the silent inter-oestrous period by the continuous 

 administration of thyroid extract, since the magnitude of 

 the motor C-R increased when this substance was fed to a 

 normal male dog (868). 



As a preliminary experiment the animal was fed thyroid 

 extract 1 gm. daily for 7 days during the inter-oestrous 

 period. The C-R was definitely not stimulated by the treat- 

 ment. The percentage of correct responses decreased and 

 the signs of nervousness were greatly intensified. Nervous 

 movements while on the platform became so violent on the 

 seventh day after the extract was begun that the equipment 

 attached to the dog was torn off and the leather straps and 

 rubber tubes were chewed apart. The experiment was then 

 abandoned for 2 weeks, then resumed. When tested after a 

 lapse of 3 months, the dog was calmer. She was then given 

 4 months' rest from the experiments. When work was re- 

 sumed, the dog was about as quiet as in the early training 

 period. However, after 2 weeks of testing the signs of the 

 nervous disturbance reappeared. 



Thyroid extract was tried again during the inter-oestrous 

 period with the same test in mind. The daily amount of the 

 substance was increased and the period of treatment was 

 lengthened. She was fed 2 gm. daily for 21 days. 



The C-R was, as before, unaffected, and again the general 

 nervousness was increased. Her escape reactions became 

 extremely violent, this time on the sixth day after the treat- 

 ment was begun. The C-R trials were discontinued for 1 

 week, but when resumed her reactions were still violent. The 

 dog was somewhat calmer 1 month after the extract was with- 

 drawn. 



Table 10 shows a marked decrease in the percentage of 

 correct responses to Met. 120 from the early training period 

 (68 per cent) to the period after the signs of the neurosis 

 appeared (30 per cent). A further marked diminution oc- 

 curred during the first thyroid experiment (30 per cent to 

 17 per cent) and the value was still below the initial level for 

 3 months after the thyroid extract was withheld (12 per cent). 



