MEN SUFFERING FROM BRAIN DISEASE.

59

animals whose motor areas have been removed somehow learn to perform the movements which they were unable to perform, the fact can not overthrow the conclusion that definite parts of the cortex are the centres particularly concerned in definite movements.

ease.

Observations of Men Suffering from Local Brain DisObservations of men suffering from local brain disease have helped to put this conclusion beyond the reach of doubt. These observations have made it possible to map out with a great deal of definiteness the areas of the brain concerned with particular movements. Not only have the centres for the legs and face been mapped out, but within the areas of these centres smaller ones have been mapped out, areas which are concerned with definite movements of the parts of the body concerned. Thus, the areas concerned with the motion of the eyelids, with the muscles of the angle of the mouth, all have their definite positions in the area for the face. "So definite," says Professor Martin, "are the positions of these areas that in cases of localized paralysis, diagnosed as due to lesions of the cerebral cortex, surgeons now have no hesitation in opening the skull in order if possible to remove the cause of trouble, as a small tumor: they know precisely in what spot they will find it."1

Said Dr. W. W. Keen: "When I say that the existence of a tumor about the size of the end of the forefinger can be diagnosticated, and before touching the head it should. be said (and I was present when the statement was made) that it was a small tumor, that it did not lie on the surface of the brain but a little underneath it, and that it lay

1 Martin's Physiology, p. 624.

partly under the centre for the face and partly under that for the arm in the left side of the brain, and that the man was operated on and the tumor was found exactly where it was believed to be, with perfect recovery of the patient,

it is something which ten years ago would have been declared the art of a magician rather than the cold precision of science." Evidence such as this may be regarded as conclusive, however difficult we may find it to explain to ourselves all the related facts.

Aphasia. Observations of persons suffering from aphasia confirm this same conclusion. As mentioned in a preceding lesson, in every case in which a post-mortem examination of the brain of a person suffering from motor aphasia has been permitted, an injury has been found in a certain definite part of the brain. The curious facts in connection with aphasia, for example, that a person has control of his voice but can not talk, or that he can write intelligently but can not talk, or that he can write but can not say what he wishes to say, or that he can write but can not read what he has written, are easily explained by the theory of localization of cerebral functions.

If we suppose the cortical centre for the control of the voice and for talking are different, it is easy to see that the injury of the one is not necessarily the injury of the other, and that, therefore, there is no necessary connection between the loss of the power to talk and the ability to control the voice. In like manner it is easy to see that the centre for writing may not be impaired, even if the association fibres that connect the writing centre with the cells concerned in the production of certain ideas are injured. Also, a person whose centre for talking is injured

HERING ON FUNCTIONS OF THE CEREBRUM. BI

will be unable to talk, but that will not prevent him from being able to write, if the writing centre is unimpaired. Nor will the fact that a person can write enable him to read what he has written if the association fibres connecting the centres concerned in seeing with the centres corresponding to the idea of what is read are injured.

Hering on the Functions of the Cerebrum.- Professor E. Hering states his conclusions as to the functions of the cerebrum in the following language: "The different parts of the hemispheres are like a great tool-box with a countless variety of tools. Each single element of the cerebrum is a particular tool. Consciousness may be likened to an artisan whose tools gradually become so numerous, so varied and so specialized that he has for every minutest detail of his work a tool which is especially adapted to perform just this precise kind of work very easily and accurately. If he loses one of his tools he still possesses a thousand other tools to do the same work, though under disadvantages both with reference to adaptability and the time involved. Should he happen to lose the use of these thousand also, he might retain hundreds with which to do the work still, but under greatly increased difficulty. He must needs have lost a very large number of his tools if certain actions become absolutely impossible."

Problem of Physiological Psychology. The assertion that each single element of the cerebrum is a particular tool specially adapted to perform a certain work in consciousness goes a long way beyond the evidence. The sensations of sight, sound, smell, touch and taste have been localized with varying degrees of probability.

But

if the famous postulate of Meynert becomes satisfactorily proved, as seems possible, the most distinctive features of the consciousness of human beings will remain unexplained. Professor James states that postulate in the following language: "The highest centres contain nothing but arrangements for representing impressions and movements, and other arrangements for coupling the activity of these arrangements together." Suppose this proved. Suppose we knew the cortical centre for each sensation and each movement, and each idea of a sensation and each idea of a movement; suppose also we knew the association fibres by means of which one sensation (cortical centre) is connected with another sensation (cortical centre), shall we have then an explanation of all the tools which consciousness uses? We shall, provided the entire mental life consists of sensations and ideas, and associations of sensations and ideas. But if this is not all of the mental life, if it leaves out of account the distinctive feature of mental life, the consciousness of relations, as I maintain that it does, then thinking (which consists in the consciousness of relations) is a part of the mental life which in the nature of the case can not be explained by the cerebrum. Upon this conception of the matter, the work possible to Physiological Psychology will have been done when Meynert's postulate shall have been satisfactorily proved in all its details. But consciousness, as the relating activity of the mind, as binding sensations into a whole of consciously related parts (concepts), and concepts. into a whole of consciously related parts (judgments), and judgments into a whole of consciously related parts (acts of reasoning), all these distinctive and unique features of the human mind must seek their explanation in a

FIG. 8.- Diagram of outer surface of left cerebral hemisphere to illustrate the localization of functions. The motor area is shaded in vertical and transverse lines: Sy, fissure of Sylvius; an, angular gyrus or convolution; Ro, fissure of Rolando; Fr, frontal lobe; Pa, parietal lobe; Te, temporal lobe. Only a very few of the more important fissures are indicated. Compare with Fig. 9. (Martin.)

FIG. 9.-Diagram of inner surface of left cerebral hemisphere to illustrate cerebrai localization. Sy, fissure of Sylvius; Ro, fissure of Rolando; Fr, frontal lobe; Oc, occipital lobe; Te, temporal lobe Cc, corpus callosum; III, third ventricle. Compare with Fig. 8. (Martin.)