722 THE BRAIN. 



(We are here, of course, viewing the action of the brain from the only 

 standpoint admissible in these pages, the purely physiological one ; but such 

 a mode of treatment does not prejudge other points of view.) Some writers 

 use expressions which seem to imply the conception that the nervous 

 changes forming the basis of the psychical and other processes of the brain 

 are chiefly the direct outcome of the chemical metabolism of the gray 

 matter and especially of the nerve-cells. They speak of " the discharge of 

 energy " from these cells in the same way that we can speak of the dis- 

 charge of energy from a cardiac fibre. But, to say nothing of the low rate 

 of nervous metabolism as measured in terms of chemical energy, we have 

 no experimental or other evidence of nervous substance in any part of the 

 body being, like the cardiac substance, the seat of an important metabolism 

 carried on irrespective of influences other than purely nutritive ones. In 

 the case of nerve- eel Is interpolated along nerves composed of fibres of the 

 same kind, as in the sporadic ganglia, all the instances where the nerve-cells 

 were supposed to initiate active processes have, on examination, broken 

 down ; as we have seen, the ganglia of the heart do not supply the moving 

 cause of the heart-beat. It is only in the central nervous system, where 

 nerve-cells, as part of gray matter, are found at the meeting of nerve-fibres 

 of different kinds, that we have any evidence of " discharge of energy " from 

 the cells. 



As we pointed out ( 510) in speaking of the spinal cord, the discharge 

 of efferent impulses from the central nervous system, though it undoubt- 

 edly must have a certain chemical basis, namely, the metabolism of the 

 nervous substance, is, in the first place, dependent on the advent of afferent 

 impulses. But this, if true of the spinal cord, is still more true of the 

 brain, which receives or may receive not only all the impulses which reach 

 it through the cord, but especially potent* and varied impulses directly 

 through the cranial nerves. All life long, the never-ceasing changes of the 

 external world continually break as waves on the peripheral endings of the 

 afferent nerves; all life long, nervous impulses, now more now fewer, are con- 

 tinually sweeping inward toward the centre ; and the nervous metabolism, 

 which is the basis of nervous action, must be at least as largely dependent 

 on these influences from without, as on the mere chemical supply furnished 

 by the blood. 



We have developed this point because of the influence it must have on 

 our conceptions of the physiological processes taking place in the cortex. 

 If we accept the view just laid down, we must regard the superemiuent 

 activity of the cortex and the characters of the processes taking place in it 

 as due not so much to the intrinsic chemical nature of the nervous substance 

 which is built up into the cortical gray matter as to the fact that impulses 

 are continually streaming into it from all parts of the body, that almost all 

 influences brought to bear on the body make themselves felt by it. To put 

 the matter in a bald way we may ask the question, What would happen in 

 the cortex if, its ordinary nutritive supply remaining as before, it were cut 

 adrift from afferent impulses of all kinds? We can hardly doubt but that 

 volitional and other physical processes would soon come to a standstill and 

 consciousness vanish. This is, indeed, roughly indicated by the remarkable 

 case of a patient whose almost only communication with the external world 

 was by means of one eye, he being blind of the other eye, deaf of both ears, 

 and suffering from general anaesthesia. Whenever the sound eye was closed, 

 he went to sleep. It is further indirectly illustrated by the following ex- 

 perimental result. We have seen ( 567) that a vertical incision carried 

 through the depth of the gray matter around an area does not prevent 

 stimulation of the surface of the area producing the usual movements. 



