664 O. D. ANDERSON 



motor C-R in the dog, reported an improvement in the per- 

 centage of correct responses to the positive and negative 

 conditioned stimuli during periods of thyroid feeding, and 

 also an increase in the magnitude of conditioned as well as 

 unconditioned responses. 



The influence of thyroid deficiency upon conditioned re- 

 flexes has also been investigated. Valkov ('23), in Pavlov's 

 laboratory, found that a thyroidectomized dog could form 

 conditioned alimentary and conditioned motor (defensive) 

 reflexes in as short a time as the normal control. The con- 

 ditioned alimentary reflex in the operated animal was, how- 

 ever, quite unstable. The conditioned motor reflex, on the 

 other hand, was stable. 



Liddell ('27), in studies on the conditioned defensive motor 

 reflex in the sheep and goat, was similarly unsuccessful in 

 demonstrating a retarding effect of thyroidectomy on learn- 

 ing. The reflex was established and maintained as well in 

 the thyroidless animals as in the normal controls. And dif- 

 ferentiations were also as easily elaborated by the former 

 as by the latter. 



In the present study concerning the thyroid and para- 

 thyroid effects, nine dogs were used. Thyroid extract was 

 administered to three and parathyroid extract to three in 

 the normal state. Four were thyroidectomized and two were 

 thyro-parathyroidectomized. The operated animals were 

 treated from time to time with thyroid extract and with 

 parathormone. 



THE EFFECT OF THYROID EXTRACT ADMINISTRATION IN THE 



NORMAL DOG 



Dog 814 $ , bassethound X Saluki F 2 . The salivary C-R was 

 used. The stimuli were Met. 120 8 (positive) and Met. 28 

 (negative). The dog was trained during a period of 14 months 

 before the critical experiments were begun. 



8 We shall henceforth refer to the metronome beating at a rate of 120 times 

 per minute (reinforced by the food or shock) as Met. 120, the metronome beating 

 42 and 28 times per minute (not reinforced) as Met. 42 and Met. 28, respectively. 



