THE MOTOR CENTERS AND THE WILL. 107 



tice would enable the other hemisphere to do the work ; but all clini- 

 cal facts say that, once destroyed, the loss is never recovered. 



If we examine this motor region of the cortex with the microscope, 

 we of course find these large corpuscles, which we have learned are 

 those which alone give energy to the muscles. But you must not 

 imagine that the motor region consists solely of these corpuscles. On 

 the contrary, as you see in this diagram, we have several layers of cor- 

 puscles. I shall return to this arrangement of the corpuscles directly. 



Looking back at the surface of the brain, you notice that I have 

 only accounted for but a small portion of the cortex. Dr. Ferrier was 

 the first to show that the portion of cortex which perceived (and I use 

 the word in its strictest sense) the sensation of light was this part, and 

 it is therefore called the " visual center or area." From recent re- 

 searches it would appear that we must give it the limits drawn on this 

 diagram ; below it we find the center for hearing. Thus we know 

 where two sense perceptive centers are situated. 



Microscopical investigation shows that this sensorial portion of the 

 cortex is very deficient in large corpuscles, and is correspondingly rich 

 in small cells. Here in this diagram you see these two kinds of struct- 

 ure in the cortex cerebri. Note the greater number and complication 

 of the small corpuscles in the sensory part of the cortex, and the com- 

 paratively fewer though much larger corpuscles in the motor region. 



It seems to me that several beliefs are justified by these facts : In 

 the first place, the movements produced by the action of these motor 

 centers are always the same for the same center ; consequently, it has 

 only one thing to do, one idea, as it were. Thus, for instance, bend- 

 ing of the arm : this action can only vary in degree, for the elbow 

 will not permit of other movements. Hence we may look upon it as 

 one idea. Now, observe that where one idea is involved we have but 

 few corpuscles. Next, consider the multitude of ideas that crowd into 

 our mind when we receive a sensation. One idea, then, rapidly calls 

 up another, and so we find anatomically that there are a corresponding 

 much greater number and complication of nerve-corpuscles. To sum 

 up, I believe we are justified in asserting that where in the nervous 

 system a considerable intensity of nerve-energy is required — e. g., for 

 the contraction of muscles — you find a few large corpuscles and fibers 

 provided ; and that where numerous ideas have to be functionalized, 

 there numerous small corpuscles are arranged for the purpose. 



But, now, the special interest attaching to the sensory perceptive 

 areas is that they, unlike the motor areas, tend to be related to both 

 sides of the body. With our habit of constantly focusing the two 

 eyes on one object, it will strike you at once that habitually we can 

 only be attentively conscious of one object at a time, since both eyes 

 are engaged in looking at it, and, as you know, we can not as a mat- 

 ter of fact look at two things at once. 



Hence, I take it, both sensory perceptive centers are always fully 



