686 



O. D. AXDF.l;S()X 



Text-figure 123 shows the effect upon the positive response. 

 Xote the sharp decline of the C-K value after the partial 

 thyroidectomy, the gradual enhancement with time and its 

 disappearance again after complete thyroidectomy. As the 

 positive responses declined in efficiency and magnitude there 

 was a decline in alertness, as is shown by the notable increase 

 in the average latent period of the C-R. The latent period 

 increased from 5 seconds to 13 seconds. 



PLtii. fflYf 



Text-figure 123. The effect of partial and of complete thyroidectomy on the 

 conditioned salivary reflex of dog 864. Note here the complete collapse of the 

 reflex value following the operation and its subsequent return to normal within 

 3 months. As was the case in dog 869, so in this case the gradual return may 

 be associated with thyroid regeneration. Note the complete disappearance of 

 the reflex after the thyroid was totally removed. 



During the entire training period, this dog gave an ex- 

 ceedingly poor showing in the differentiation tests. In view 

 of this it is remarkable that when the tests were resumed 

 during the post-operative period, there should be evidence 

 of marked improvement. As the positive C-R began to revive 

 after the first operation, and before it had recovered its full 

 strength, we tried not only the usual negative differential 

 stimuli Met. 28 and Met. 42, but entirely new ones in relation 



