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the source of irritation is withdrawn. Thus I have seen redness 

 which had existed for about three days in the human skin in con- 

 sequence of tight stitches connecting the lips of a wound, give place 

 at once to pallor on their removal. Had the arterial dilatation in 

 this case been the result of nervous exhaustion continued during so 

 long a period, such speedy recovery could hardly, one would think, 

 have taken place. 



These and other considerations, to which the already excessive 

 length of this letter forbids me to allude, induce me to think it 

 safest in the present state of science to regard as a fundamental 

 truth not yet explained, that one and the same afferent nerve may, 

 according as it is operating mildly or energetically, either exalt or 

 depress the functions of the nervous centre on which it acts. It is, I 

 believe, upon this that all inhibitory influence depends, and I suspect 

 that the principle will be found to admit of a very general applica- 

 tion in physiology. 



I am, &c., 



JOSEPH LISTER. 



