Page:Popular Science Monthly Volume 11.djvu/351

Rh hair grows gradually. The fits become simple convulsions, then mere twitchings, and lastly the animal can no longer be distinguished from another healthy one but by the fact that it has only one toe at one of its hind-legs, when the operation has been performed on the sciatic nerve; and nothing whatever remains when the origin of the disease was a prick in the spinal cord.

All these different facts, of which I have just spoken, are the characteristics of an epileptic seizure in our own species. That zone of skin about the neck and face is the analogue of those areas of the body of the epileptic from which sensations of all possible natures and kinds arise a short time before the attacks, and which are called by the general name of "aura."

To make the analogy greater, let me say that, just as in man, when such an "aura" is discovered to start from such a part of the body that it can be acted upon directly, so as to be removed, the disease is cured, so also, if that zone, of which I have spoken, in the Guinea-pig be cauterized, the fits do not occur—the animal is cured.

I have given these details with some minuteness, because they show still more strongly the effects of hereditary transmission of the disease. All the young of Guinea-pigs thus made the subject of experiment do not become epileptic; Dr. Brown-Séquard has observed several. I have had occasion to observe only a very few, and I have been able to learn that the young are born healthy, apparently. Sometimes—almost always, in fact—they are born with only one toe in the hind-leg; that is the case when the parent had lost its toes in the manner that I have already stated. Perhaps two months or more after their birth—they become adult very rapidly—the same phenomena develop in those young as in their parents; to use the words of Dr. Brown-Séquard himself, "we see the gradual increase of the affection, the diminution of the sensibility in the zone, just as with the parent, the coming of a period of complete attacks of epilepsy, and then the loss of hair, and the gradual diminution of the nervous complaint." Now, it is to be observed—and this is the important feature in this transmission of disease—that in the parent operated upon the cure, when it is spontaneous (that is, when it does occur without any treatment, which is the case when the sciatic nerve and not the spinal cord has been divided), only supervenes because the alteration in the nerve is cured: if it has been sectioned, the two ends meet again and are reunited after a few weeks; if it has been torn away, the parts still remaining attached to the outer heal together; we can therefore understand how, the cause of the disease, i. e., the alteration of a nerve, being removed, the disease, i. e., epilepsy, also disappears. But in the young which have inherited the taint no such explanation obtains. Their nerves have not been operated upon, not torn nor cut. How are we to explain their cure, and this fact, which is, as I have said, the peculiar feature of this