746 O. D. ANDERSON 



equally strong. This indicated the relatively low threshold 

 of stimulation. After the operations, the same positive 

 stimulus was not capable of evoking its former strong positive 

 response but gave only a weak response or none at all. The 

 negative stimulus now evoked no observable reactions. Both 

 types of stimulation fall below the threshold, but the negative 

 further below than the positive. 



The increase in responsiveness in the animals following 

 the administration of the various extracts can similarly be 

 interpreted as due to a rise in the level of excitation. 



We may inquire as to the way in which the disturbance 

 of the gland produces alterations in the level of nervous 

 excitability. The explanation of this probably concerns the 

 chemistry of the nerve cell and its surrounding medium. 

 Disturbance of the internal secretions results, of course, in 

 a general disturbance of the chemical equilibrium of all body 

 fluids. A change in the metabolism of the salts of the metallic 

 elements, for example, may modify nervous function, and 

 such changes are probably closely related to changes in the 

 endocrine secretions. The ablation of a gland of internal 

 secretion may alter the juices surrounding the nerve cell 

 in such a way as to bring about a fall in the level of ex- 

 citability. 



The Probable Role of the Glands in the Production of 

 Behavioral Types in the Dog 



The differences between the behavioral types observed by 

 James may be thought of as definitely bound up with funda- 

 mental differences in nerve function, which in turn are as- 

 sociated in some way with congenital and inheritable 

 differences in the internal secretions. The excitable, the in- 

 hibitive, and the intermediate types possess respectively high, 

 low and intermediate levels of excitation. In the present 

 experiments, the behavior of the intermediate type was caused 

 to vary in the direction of either extreme. The excitability 

 level was raised by thyroid extract and by adrenalin, so that 

 the behavior for a time was suggestive of the excitable type. 



