198 PROBLEMS OF GENETICS 



to confirm Brown-S6quard, others finding evidence which in 

 various degrees supported his conclusions. Recently a new and 

 especially valuable paper has been published by Mr. T. Graham 

 Brown 10 which goes far towards settling this outstanding question. 

 He states that "the Brown-S6quard phenomenon is nothing more 

 or less than a specific instance of the scratch-reflex," and it is 

 due to a raised excitability of the mechanism of this reflex. This 

 raised excitability is the character acquired as a consequence, 

 for instance, of the removal of part of one great sciatic nerve. 

 The nature of this raised excitability and its causation are dis- 

 cussed and elucidated, but this part of the work is not essential 

 to the present consideration. Mr. Graham Brown in his summary 

 of conclusions remarks that it is very difficult to see how this con- 

 dition of raised excitability can be transmitted to the offspring, 

 and this comment which might be made in reference to any of 

 the alleged cases certainly applies with special cogency to the 

 present example. 



He then calls special attention to three observations: 



1. That guinea pigs which had a " trophic " change in the 

 foot, as a result of division of the great sciatic nerve, have re- 

 peatedly been seen to nibble the feet of other guinea pigs which 

 had this change in the foot from the same causes. 



2. That accidental injury to the toes may be followed by the 

 Brown-S6quard phenomenon in an otherwise normal animal. 



3. That in several instances the young of guinea pigs which 

 exhibited the phenomenon have been noticed to have one or more 

 toes eaten off by the mother. 



Brown-Sequard noticed that almost all his animals in which 

 the great sciatic was divided acquired the " epilepsy " and 

 nibbled those parts of their feet in which sensation had been lost. 

 Of the offspring of such animals he found that a very small pro- 

 portion exhibited a malformation of the feet, and of these some 

 showed the " epilepsy." The proportion which showed the 

 " epilepsy " was one to two per cent, of the offspring. 



Morgan 11 is quoted by Graham Brown as having suggested 



10 T. Graham Brown, Proc. Roy. Soc., 1912, vol. 84, B, p. 555. This paper gives 

 full reference to the previous literature of the subject. 



11 Morgan, T. H., Evolution and Adaptation, New York, 1903. 



