ON HEREDITY IN NERVOUS DISEASES. 337 



hair grows gradually. The fits become shnple 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 dis- 

 ease 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 eflfects of hereditary transmission of 

 the disease. All the young of Guinea-pigs thus made the subject 

 of experiment do not become epileptic; Dr. Brown -Sequard 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 rapid- 

 ly the same phenomena develop in those young as in their par- 

 ents ; to use the words of Dr. Brown-Sequard himself, "we see the 

 gradual increase of the aiFection, 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 diminu- 

 tion 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 super- 

 venes because the alteration in the nerve is- cured : if it has been sec- 

 tioned, 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 dis- 

 ease, 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 oper- 

 ated 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 

 VOL. XI. 22 



