IN THE THEORY OF NATURAL SELECTION. 313 



cardine disease of the silkworm. At all events we can understand 

 in this way how it happened that the offspring- of artificially 

 epileptic guinea-pigs were affected with various forms of nervous 

 disease, a fact which would be quite unintelligible if we assume 

 the occurrence of a true hereditary transmission of a morpho- 

 logical character, such as a pathological change in the structure of 

 some nervous centre. 



The manner in which artificial epilepsy becomes manifest after 

 the operation, is also in favour of the explanation offered above. 

 In the first place epilepsy does not result from any one single 

 injury to the nervous system, but it may follow from a variety 

 of different injuries. Brown-Sequard produced it by removing* 

 a portion of the grey matter of the brain, and by dividing 

 the spinal cord, although the disease also resulted from a trans- 

 verse section through half of the latter organ, or from the section of 

 its anterior or posterior columns alone, or from simply puncturing 

 its substance. The most striking effects appeared to follow when 

 the spinal cord w r as injured in the region between the eighth 

 dorsal and the second lumbar vertebrae, although the results were 

 sometimes also produced by the injury of other parts. Epilepsy 

 also followed the division of the sciatic nerve, the internal popliteal, 

 and the posterior roots of all nerves which pass to the legs. The 

 disease never appears at once, but only after the lapse of some 

 days or weeks, and, according to Brown-Sequard, it is impossible 

 to conclude that the disease will not follow the operation until 

 after six or eight weeks have passed without an epileptic attack. 

 Obersteiner did not witness in any case the first symptoms of the 

 disease for several days after the division of the sciatic nerve. 

 After the operation, sensibility decreases over a certain area on 

 the head and neck, on the same side as the injury. If the animal 

 be pinched in this region (which is called the epileptic area, ' zone 

 epileptogene ') it curves itself round towards the injured side, and 

 violent scratching movements are made with the hind leg of 

 the same side. After the lapse of several days or even weeks, 

 these scratching movements which result from pinching in the 

 above-mentioned area, form the beginning of a complete epileptic 

 attack. Hence the changes immediately produced by the division 

 of a nerve are obviously not the direct cause of epilepsy, but they 

 only form the beginning of a pathological process which is con- 



