DISCOVERY 



339 



and perception — all are quite independent of our know- 

 ledge of any accompanying nervous activities. Even 

 if we did know the functions and the conditions of 

 activity of every particle of nervous substance within 

 the bodj', the need for psychological investigations 

 would still remain. Physiology can never describe a 

 mental process, but only the neural process with which 

 it is somehow correlated. 



The independence of psychology is even still more 

 evident in its applications. Psychology has now 

 reached the stage of being an Applied Science. In 

 medicine, it has established a new point of view in the 

 treatment of certain mental and nervous disorders, the 

 " psychogenic " ' character of which has now in many 

 cases been clearly shown, and the cure of which must 

 therefore be conducted primarily from a psycho-thera- 

 peutic standpoint. In education, the importance of 

 considering individual interests and mental differences, 

 of investigating the effects of formal training and the 

 relation of general to sj>ecific abilities, and of adapting 

 the curriculum to the psychology of the child instead 

 of to that of the adult, has become more and more clearly 

 recognised. In industry, applied psychology is deter- 

 mining the most economical methods of work, alike as 

 regards the best movements to be learnt, the best dis- 

 tribution of p)criods of work and rest, and the foundation 

 of mental tests which will select those best fitted for 

 different kinds of work. Unfortunately, some of the 

 most ardent advocates of the applications of psychology 

 to education, industry, and medicine have themselves 

 received inadequate training in pure psychologj'. The 

 consequent initial result has been to establish narrow 

 "schools " of psycho-therapeutics, education, etc., and 

 an uncritical hero-worship of these worthy pioneers. 

 But the more judicially minded psychologist may easily 

 forgive the blind enthusiasm and antagonism which 

 such revolutionary changes have had to meet. 



In jurisprudence, psychology is fast making its in- 

 fluence felt. The hitherto unjust criteria of criminal 

 responsibility are being modified in the light of increas- 

 ing psychological knowledge. The value of legal evi- 

 dence is being considered in the light of recent psycho- 

 logical experiments on the degree of accuracy, detail, 

 and subjective assurance with which an experience is 

 revived, on the influence of time, suggestion, etc. In 

 art, psychology is founding an experimental science of 

 esthetics. In biology, psychology has done excellent 

 work on the study of the behaviour of animals, and in 

 ethnology on the study of different races. In religion, 

 in economics, in history, in linguistics, it is Ukewise fast 

 proving its value. But how are all these instances 

 of the applications of psychology of interest for physi- 

 ology ? 



I have left untouched one class of research in which it 

 ' Having psychical causation. 



might be supposed that psychological knowledge has 

 been dependent on physiological experiment. I refer 

 to the effects of experimental, accidental, or morbid 

 lesions - of the central and peripheral human nervous 

 system upon mental activity. In particular I refer 

 to the striking researches of Henry Head and his col- 

 laborators. Rivers, Gordon Holmes, and Riddoch. But 

 these researches are to my mind primarily psychological, 

 not physiological. They have involved the careful 

 application of psychological tests and psycho-physical 

 methods to individuals whose nervous system is no 

 longer intact. They demand psychological rather than 

 phj'siological training for their final interpretation. In- 

 deed, they have taught the psychologist to be chary of 

 the evidence adduced in the field of physiological 

 psj'chology. Thus Head's most recent work on aphasia 

 (now on the eve of publication) has given the final death 

 blow to those diagrammatic schemes of speech centres, 

 with their visual, auditory, and kinjcsthetic ' memory 

 centres, which physicians so long believed they had 

 scientifically demonstrated and psychologists credu- 

 lously accepted, under the stultifying influence of 

 bygone notions of the storing up of images in special 

 centres, the mistaken confusion of imagery with 

 meaning and of thought with language, and the 

 erroneous conceptions of separate watertight mental 

 faculties. 



Head's earlier work has revealed the complex nature 

 of apparently simple processes, and confirmed the 

 psychologist in liis growing disbelief in the sufficiency 

 of ordinary introspection, and in his realisation of the 

 importance of the lower unconscious regions for the 

 effective acti\aty of the higher. It has also afforded 

 valuable examples of the acceptance, inhibition, or 

 fusion of compatible or incompatible sensory processes 

 and of the control exercised by higher over lower mental 

 systems. 



Nevertheless, the exact significance of many of the 

 results of these investigations for psychology is quite 

 uncertain. Because a man walks with a certain char- 

 acteristic gait when certain nervous paths are affected 

 by disease, it would be fallacious to assume that this 

 gait illustrates a primitive form of progression. So, 

 too, because in certain lesions abnormal mental states 

 make their appearance, one must not necessarily infer 

 that these have had an independent existence in man's 

 normal intact ancestry. Again, it would be unsafe to 

 assume, because the existence of two forms of cu- 

 taneous * sensibility is indicated by observations chiefly 

 made during the regeneration of divided sensory nerves, 

 that these two systems have separately originated at 

 different periods during men's past evolution. It may 



• Lesion, a disturbance of normal structure. 

 ' Relative to the sensations of movement. 



* Relating to the skin. 



