May 20, 1920] 



NATURE 



l^i 



all the elements to the theoretical scientist on account 

 of the romantic history of its discovery, its occurrence 

 in a remarkable condition of solid solution in many 

 minerals, its formation as a product of the disintegra- 

 tion of the radio-active elements, its liquefaction after 

 a decade of unsuccessful attempts by some of the 

 world's greatest experimenters, the attainment by its 

 use of temperatures below those at which the resist- 



ances of pure metals vanish, its many unique physical 

 properties, and the many important theoretical con- 

 clusions which have been drawn from its behaviour. 



All of these points of interest have been the subjects 

 of very thorough investigation. The important 

 developments of the future will probably be along the 

 line of the applications of helium, many of which 

 have already been suggested. 



New Conceptions of Psychology. 



THE results of Dr. Henry Head's clinical in- 

 vestigations 1 are exceptionally interesting 1 

 from the philosophical point of view, for they are 

 utterly incompatible with the older ideas of the | 

 introspective psychologists. In fact, his work is i 

 ' ' a complete scientific refutation of all psychologi- 

 cal theories which build up knowledge out of ori- 

 ginal sense-material " (Nature, November 6, 1919, 

 p. 267). Dr. Head has demolished the old psycho- 

 logy and created a new conception, in accordance { 

 with which "sensations depend neither for their 

 existence nor for their psychical quality on the | 

 cerebral cortex, which has a purely interpretative i 

 function in regard to them." | 



The function of the cerebral cortex in sensa- i 

 tion is to endow it with spatial relationships, with 1 

 the power of responding in a graduated manner to 

 stimuli of different intensities, and with those 

 qualities by which we recognise the similarity or 

 difference of objects brought into contact with the 

 body. The old psychologists held that there was 1 

 something in the external universe correspond- \ 

 ing to primary sensations, which they regarded as 

 being combined into the elements of perception. 1 

 In accordance with such views the changes at the i 

 periphery were simple and became more complex ; 

 the nearer they approached the highest centres in 

 the brain. By submitting himself to a surgical \ 

 operation in 1905 Dr. Head was able to demon- 

 strate the complexity of the peripheral changes ' 

 and the diffuseness of the impressions received. | 

 Moreover, by his clinical studies- — monuments of ! 

 patient research and marvellous insight — he has 

 shown how these multitudes of diffuse peripheral 

 changes gradually become integrated and ren- 

 dered more specific in quality, space, and time as 1 

 they approach the highest physiological levels in 

 the central nervous system. The recognition of 

 these facts gives an indication of the mode by 

 which evolution has brought into existence such a \ 

 nervous system as that of man. Lower, more | 

 impulsive, and less specific reactions become domi- 

 nated by those that admit of choice. This con- 

 ception turns orthodox psychology upside down. 



Man's conceptions of space, time, and material 

 rest ultimately on the nature of the spatial and [ 

 temporal elements in sensation. These in turn 1 

 are founded on complex physiological activities, | 

 many of which may never disturb consciousness i 

 directly ; although they do not enter into the i 

 province of introspective psychology, they are re- 

 sponsible for much that is usually attributed to 



1 " Sensation and the Cerebral Cortex," Brain, vol. xli., part ii., 1918. 



NO. 2638, VOL. 105] 



the action of the mind. Dr. Head's work on the 

 cerebral cortex represents the culmination of an 

 intensive investigation of the sensory system upon 

 which he has been engaged for more than a 

 quarter of a century. In 1893 he was studying the 

 phenomena of the localisation of the pain asso- 

 ciated with visceral disturbances and incidentally 

 mapping out the distribution of the sensory 

 nerves. Then he began the analysis of the com- 

 ponents of the sensory nerves ; and to test the 

 problems that called for solution he invited Mr. 

 James Sherren to cut one of the main sensory 

 nerves of his (Head's) arm, and with the help 

 of Dr. Rivers he studied the process of the re- 

 storation of function in the severed nerve. By 

 this means he was able to differentiate between 

 the three kinds of sensory nerves distributed to 

 his arm : — 



(a) The deep afferent system supplying the con- 

 nective-tissues, muscles, joints, and tendons, in 

 virtue of which is conferred the power of recog- 

 nising movement and appreciating the position 

 of any part of the limb, as well as of localising 

 pressure and responding to certain aspects of 

 pain ; 



(b) A punctate afferent mechanism in the skin, 

 which Dr. Head has called "protopathic," the 

 primitive nature of which is shown by the early 

 restoration to activity (a little more than six 

 weeks in Dr. Head's arm) of its end-organs after 

 the nerve has been reunited, by the specific nature 

 of the response of each set of end-organs, and 

 by the diffuse " all-or-nothing " nature of the re- 

 sponse, i.e. the absence of any graduation corre- 

 sponding to the intensity of the stimulus ; and 



(c) Superimposed over this older mechanism 

 another cutaneous system of later development 

 and higher functions, which Dr. Head calls " epi- 

 critic. " Epicritic sensibility is not restored for 

 many months after the reappearance of proto- 

 pathic sensibility, the diffuse reaction of which is 

 then checked and controlled ; and the effects of 

 stimulation are modulated according to the in- 

 tensity and locality of the exciting agent. It is 

 concerned with the finer degrees of tactile and 

 thermal discrimination and is opposed to, and 

 controls, the diffuse "all-or-nothing" reaction of 

 protopathic sensibility. 



It has long been known that the sensorv paths 

 in the central nervous system had a twofold 

 terminus, represented by the thalamus and the 

 cerebral cortex. It remained for Dr. Head to in- 

 terpret the meaning of this arrangement. He 



