io8 THE POPULAR SCIENCE MONTHLY. 



occupied with the same object at the same moment, and that therefore 

 we have complete bilateral representation of both sides of the body in 

 each hemisphere. As a further consequence, each sensory perceptive 

 area will register the idea that engaged it ; in other words, both cen- 

 ters will remember the same thing. Thus it happens that each sensory 

 area can perform the duty of the other, and therefore it is a matter of 

 comparative indifference whether one is destroyed or not, and as a mat- 

 ter of fact when this happens we find that the person or animal recog- 

 nizes objects as they actually are, and in fact has no doubt as to their 

 nature. Here you see anatomically the reason of this peculiarity is 

 found to be that the optic or seeing nerves cross one another incom- 

 pletely in going to each hemisphere, and thus each sensory center rep- 

 resents half of each eyeball. 



I must pass rapidly to the description of the rest of the surface of 

 the brain — the hinder and front ends. At the outset I must admit 

 that all our knowledge concerning them is very hypothetical in the 

 absence of positive experimental results. 



This much we can say, that they are probably the seats of intel- 

 lectual thought, for many reasons which I have not time to detail. 

 Further, we know that these intellectual areas are dependent for their 

 activity entirely on the sensory perceptive centers, for the dictum that 

 there is no consciousness in the absence of sensory stimulation is very 

 well established, as I shall now show you, however astounding it may 

 appear. In the first place, you will remember that when we wish to 

 encourage that natural loss of consciousness which we call sleep, we 

 do all we can to deprive our sense-organs and areas of stimulation. 

 Thus we keep ourselves at a constant temperature, ■vse shut off the 

 light, and abolish all noises if we can. But a most valuable observa- 

 tion was made a few years ago by Dr. Strurapell, of Leipsic, who had 

 under his care a youth, the subject of a disease of the brain, etc., 

 which, while destroying the function of one eye and ear, besides the 

 sensibility to touch over the whole body, still left him when awake 

 quite conscious and able to understand, etc., using his remaining eye 

 and ear for social intercourse. Now, when these were carefully closed 

 he became unconscious immediately, in fact slept, and slept until he 

 was aroused again, or awoke naturally, as we say, after some hours. 

 Hence the higher functions of the brain exercised when that organ is 

 energizing the reasoning of the mind are absolutely dependent upon 

 the reception of energy from the sense perceptive areas. 



But my only point with reference to this part of the brain is to 

 attempt to determine how far they are connected with the motor cen- 

 ters in the performance of a voluntary act. With the mechanism of 

 choice and deliberate action I have nothing to do ; but there can be 

 no doubt that the part of the brain concerned in that process of the 

 mind is directly connected with the motor region, as indicated on this 

 diagram, to which I would now return. From what I have here writ- 



