1911.] 



the Transmission of Acquired Characters. 



567 



spinal dog the scratching movements are usually confined to the hind limb of 

 the side stimulated. Gergens(29) and, later, Magnus (50) have, however, 

 shewn that the scratch may appear in the contralateral hind limb if the 

 ipsilateral limb is restrained. The present author has observed the same 

 phenomenon in a guinea-pig which only exhibited the " incomplete " Brown - 

 Sequard phenomenon. 



But in the " narcosis scratch " — a phenomenon, moreover, which appears in 

 normal guinea-pigs — the scratching movements also alternate from side to 

 side of the body. 



It is therefore possible, and indeed probable, that the scratch-reflex is in 

 a state of great potential excitability — upon that side of the body on which 

 the great sciatic nerve has been cut — in a guinea-pig which exhibits the 

 " complete " Brown-Sequard phenomenon. The first resultant of the 

 effective stimulus will be to evoke the scratch-reflex in the hind limb of that 

 side. At a certain point, however, the condition passes over into a state 

 which parallels that condition seen in the " narcosis scratch." 



From a consideration of these phenomena I think that there can be no 

 reasonable doubt that the phenomena described by Brown-Sequard are 

 special instances of states — the true scratch-reflex and the "narcosis 

 scratch " — of which the conditioning mechanisms are inherent in all normal 

 guinea-pigs. 



If this be true, the Brown-Sequard phenomenon must not be regarded as 

 a specific condition specifically created by the consequences of certain lesions 

 of the nervous system, and thus as arising de novo in the animals so treated. 

 It must rather be looked upon as being in itself an expression of the activity 

 of a mechanism present in all guinea-pigs and only especially elicitable in 

 consequence of the derangements produced by these lesions. 



If the mechanism is present in all guinea-pigs it is equally present in the 

 young of parents in which the Brown-Sequard phenomenon is present. But 

 if this phenomenon is present in these young what is inherited as an 

 acquirement is not the mechanism but the especial excitability of it. 



IV. Conclusions Concerning the Cause of the Brown-Sequard Phenomenon. 



The question now arises — in what manner does the section of the great 

 sciatic nerve produce the raised excitability of this mechanism ? 



Abel and Graham Brown have partially discussed this question (51). The 

 special question examined by them was the causation of macroscopic and 

 microscopic changes in the " epileptogenous zone " of skin from which the 

 movements of the phenomenon are elicited by mechanical stimulation. 

 This question concerns us here. 



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