740 O. D. ANDERSON 



sistent with this observation is the fact that the percentage 

 of efficiency of the negative in the early castrate, also, is 

 much higher than the average figure for normal animals. 

 This fact is another way of illustrating the lowered level of 

 excitability. The diminished C-E was accompanied in two 

 dogs by a lowered degree of activity in general responsiveness. 



DISCUSSION 

 COMPARISON AND CORRELATION OF THE RESULTS 



The results of the various phases of this investigation lead 

 to the general conclusion that the endocrine glands play an 

 important role in the nervous responsiveness of dogs. Ad- 

 ministration of gland extracts to normal dogs raised the 

 threshold of excitation so that the fundamental nervous 

 responses were to some extent easier to arouse, while on 

 the other hand, the removal of a gland resulted in a lowering 

 of excitation and the reactions were more difficult to arouse. 

 The administration of extracts of the thyroid, the para- 

 thyroids, the anterior pituitary and the adrenal medulla all 

 resulted in an increased excitability towards controlled ex- 

 ternal stimulation given under exact laboratory conditions. 

 Extirpation of the thyroid, the thyroid and parathyroids, 

 the pars anterior of the pituitary, the suprarenals and the 

 gonads results in a marked lowering of the nervous respon- 

 siveness under the same conditions. 



That the post-operative diminution in responsiveness was 

 due in some way to a deficiency of the hormone elaborated 

 by the gland in question was directly indicated in the case 

 of the thyroid, parathyroids, the anterior pituitary and the 

 suprarenals by the fact that the weakened C-R was definitely 

 strengthened through the introduction of an extract contain- 

 ing the active principle of the gland thyroid substance, 

 parathormone, anterior pituitary extract and extract of the 

 adrenal cortex. The fact that the reaction was not fully 

 restored to the previous or normal level was probably due 

 in part to the imperfection of the available gland extracts, 



