BIOLOGY IN RELATION TO OTHER NATURAL SCIENCES. 453 



Franklin,* that each of the elements of the visual apparatus is made up 

 of a central structure for the sensation of light and darkness, with 

 collateral ai)pendages for the sensations of color — it being of course 

 understood that this is a mere diagrammatic representation, which 

 serves no purjjoses beyond that of facilitating the conception of the 

 relation between the several '^specific energies." 



EXPERIMENTAL PSYCHOLOGY. 



Resisting the temptation to pursue this subject further, I will now 

 ask you to follow me into a region which, although closely connected 

 with the subjects we have been considering, is beset with greater diffi- 

 culties — the subject in which, under the name of physiological or 

 experimental psychoU)gy, i)hysiologists and psychologists have of late 

 years taken a common interest — a borderland not between fact and 

 fancy, but between two methods of investigation ^f questions which 

 are closely related, which here, though they do not overlap, at least 

 interdigitate. It is manifest that, quite irrespectively of any foregone 

 conclusion as to the dependence of mind on processes of which the 

 biologist is accustomed to take cognizance, mind must be regarded as 

 one of the "specific energies"' of the organism, and should on that 

 ground be included in the subject-matter of physiology. As however 

 our science, like other sciences, is limited not merely by its subject but 

 also by its method, it actually takes in only so much of psychology as 

 is experimental. Thus sensation (although it is psychological), and the 

 investigation of its relation to the special structures by which the mind 

 keeps itself informed of what goes on in the outside world, have always 

 been considered to be in the physiological sphere. And it is by ana- 

 tomical researches relating to the minute structure and to the develop- 

 ment of the brain, by observatimi of the facts of disease, and, above all, 

 by physiological experiment, tluit those changes in the ganglion cells 

 of the brain and spinal cord which are the immediate antecedents of 

 every kind of bodily action have been traced. Between the two (that 

 is, between sensation and the beginning of action), there is an inter- 

 vening region which the physiologist has hitherto willingly resigned to 

 psychology, feeling his incompetence to use the only instrument by 

 which it can be explored — that of introspection. This consideration 

 enables us to understand the course which the new study (1 will not 

 claim for it the title of a new science, regarding it as merely a part of 

 the great science of life) has hitherto followed, and why physiologists 

 have been unwilling to enter on it. Tlie study of the less complicated 

 internal relations of the organism has afrbrded so many difficult prob- 

 lems that the most difficult of ail have been deferred; so that although 

 the psycho-physical method was initiated by E. H. Weber in the mid- 



* Christine Ladd Franklin, " Eine neue Theorie der Liohtempfiudungeu," Zeitschr 

 fiir Psycholofjie, 1893, vol. iv, p. 211; see also the Proceedings of the last Psycholog- 

 ical Congress in London, 1892. 



