1911.] 



the Transmission of Acquired Characters. 



575 



scratch-reflex. The " incomplete " reaction resembles the true scratch- 

 reflex. The " complete " reaction resembles to a certain extent the 

 " narcosis scratch " described by the author. 



2. The true scratch-reflex may be evoked in normal guinea-pigs, and so 

 may be the scratching phenomena of the narcosis scratch. 



3. The Brown-Sequard phenomenon is due to a raised excitability of the 

 scratch-reflex. 



4. What especially is acquired as a consequence, for instance, of the 

 removal of part of one great sciatic nerve, is a state of raised excitability of 

 the mechanism which subserves the scratch-reflex. 



5. The question of the alleged transmission of this phenomenon to the 

 young of animals in which it is present therefore resolves itself into the 

 question of the transmission of an acquired state of raised reflex excitability 

 of the scratch-reflex. 



6. Experiments here described prove that the state of raised excitability 

 of the scratch-reflex in the parent is not clue to the continued irritation 

 caused by the formation of a cicatrix round the stump of the divided nerve. 

 For division of the nerve again above the stump does not abolish the 

 phenomenon. 



7. Experiments also shew that the condition has no fixed relationship to 

 the presence or to the absence of degenerative changes which sometimes 

 occur in the foot after severance of the nerve. 



8. Observations also shew that the phenomenon may occur in animals in 

 which there is no " trophic " change in that area of the skin of the face and 

 neck (" epileptogenous zone " of Brown-Sequard) from which the reaction is 

 evocable by the application of mechanical pressure. The phenomenon may 

 also occur when such a change is present there. This change is therefore 

 probably not the intrinsic cause of the condition. 



9. The suggestion is put forward that the raised excitability of the 

 scratch-reflex, which conditions the phenomenon, is due to the removal of an 

 inhibitory influence normally exerted by the great sciatic nerve and its 

 branches. 



10. It may be supposed that, in the " neural balance " of the scratch-reflex, 

 one of the inhibitory factors is conditioned by the activity of the afferent 

 fibres contained in the great sciatic nerve, and that, when this factor is 

 removed by division of the nerve, the excitatory factors are less completely 

 balanced, and the neural balance is tilted in the direction of excitability. 



11. The raised excitability of a certain number only of the individual 

 reflex arcs, which together compose the scratch-reflex, may lead to a state of 

 incoordination in all the other arcs, so that, when a normal stimulus tends 



