512 Journal of Coinparative Neurology and Psvchology. 



Few will venture to deny probability to the assumtion that 

 modifiability of reaction varies in degree, not in kind ; yet. if 

 abilit}' to profit by experience is to be a satisfactory criterion 

 of the ps}'chic there must be either reference to a difference in 

 kind of modifiabilit}-, or the choice, by those who attempt to 

 use the criterion, of an arbitrarily selected degree or rapidit}' 

 of change in reaction as indicative o{ tlie transition from the 

 non-psychic to the psychic. 



At this point there are at least two possibilities : either we 

 may choose a certain standard of modifiableness as indicative of 

 the psychic reaction, or we may seek for other characteristics 

 in addition to modifiability as means of distinguishing the 

 psychic from the non-psychic in organic reaction. That the 

 latter alternative is the more desirable of the two all who have 

 attempted to use the criterion of abilit}- to profit b)- experience 

 will grant more or less freely, according to their various preju- 

 ijices. 



Although the ph}-siologist deals primarih- with the non- 

 psychic, he is no more able to ignore the psychic than is the 

 chemist to avoid the use of physical concepts and terms. Similarly 

 the psychologist is dependent upon the ph)'siologist, and in turn 

 upon the ciiemist and physicist, as is the physiologist himself. 

 Granting validity and scientific value to the separation of reac- 

 tions into the psychic and non-psychic, the existence of physi- 

 ology and psN'chology as coordinate sciences needs no justifi- 

 cation. Both are natural sciences ; both deal with organic re- 

 actions. From certain points of view the psychic reaction is 

 more difficult of description than the non-psychic, but the same 

 methods of investigation apply to the two classes of reaction. 

 Ph)'siologists and psychologists must cooperate in discovering, 

 and must agree upon the distinguishing characteristics of the 

 psychic and the non-psychic reaction. By mutual agreement 

 they must fix the limits of their sciences. 



The most keenly felt need at present in the science of or- 

 ganic reaction is for careful, detailed, patient, and extensive 

 study of the forms and modifications of reaction. Whether 

 physiologists or psychologists, we must know our materials 



