Page:Popular Science Monthly Volume 74.djvu/569

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And, first, it would seem that the cerebral hemispheres, including their integuments, are largely or completely devoid of the capacity of self-feeling. It has been known for some time that the substance of the brain is insensitive to pain; but it has hitherto been held that the dura is a highly sensitive tissue. This belief was strengthened by the knowledge that this membrane receives its innervation from the trigeminal nerve, and by the experience that in trephining the lower animals, when the dura is reached, struggling, and rise in blood-pressure are common. But here was a fully conscious subject, able intelligently to describe his sensations, who felt no pain while the membranes over that part of the brain which is allotted to sensory impressions were incised and manipulated. This experience, therefore, throws back upon us the problem: What is it that causes intracranial pain, especially in the form of those intense headaches which follow upon disturbances of the cerebral blood-supply, or in cases of cerebral lesion like that now under discussion? May we not find that the causes of the pains which we locate in the cerebral hemispheres invariably lie outside of those hemispheres? Certainly, it is not strange that the localization in such cases should be even more indefinite than in the case of an aching tooth or some form of abdominal distress. Indeed, cerebral pains and other forms of discomfort, with their accompanying mental disturbances, may be so severe as to result in insanity, and yet the location of the irritating causes, whether nearby or remote from the brain, remain undiscovered.

Second, there is both additional light and increased confusion contributed by these cases of cerebral surgery without anesthetics to the problem of the functions of the post-central and so-called sensory convolutions. In both these cases stimulation of the motor strip called out motor responses; stimulation of the post-central area failed to call out motor responses. More important still by far is the fact that, in the second case, stimulation of the post-central convolutions was followed by distinct sensory impressions—not mere signs of such impressions, but conscious sensations, testified to in language by their subject; and these sensory impressions were located in the extremities and not at all in the cortex itself. This is definite and fairly conclusive evidence to the functional value of the post-central convolutions. But now, on the other hand, we have the fact that, although the incision was made in the middle of the field supposed to be especially if not exclusively sensory, no subjective sensations whatever were called forth in this way; and the yet more startling fact—T quote the words of Dr. H. M. Thomas, clinical professor of neurology in Johns Hopkins University—that.

With a tumor situated in large part in the post-central convolutions and involving a considerable portion of its superior part, there was practically no objective sensory loss. I think it may fairly be said that before the first