THE NERVOUS SYSTEM. 471 



bling the spirituous part of white of egg, and resid- 

 ing in the nerves. This hypothesis, of a very subtle 

 humour or spirit existing in the nerves, was indeed 

 very early taken up 15 . This nervous spirit had been 

 compared to air by Erasistratus, Asclepiades, Galen, 

 and others. The chemical tendencies of the seven- 

 teenth century led to its being described as acid, 

 sulphureous, or nitrous. At the end of that cen- 

 tury, the hypothesis of an ether attracted much 

 notice as a means of accounting for many pheno- 

 mena; and this ether was identified with the ner- 

 vous fluid. Newton himself inclines to this view, in 

 the remarkable Queries which are annexed to his 

 Opticks. After ascribing many physical effects to 

 his ether, he adds (Query 23), " Is not vision per- 

 formed chiefly by the vibrations of this medium, 

 excited in the bottom of the eye by the rays of 

 light, and propagated through the solid, pellucid, 

 and uniform capillamenta of the nerves into the 

 place of sensation?" And (Query 24), "Is not 

 animal motion performed by the vibrations of this 

 medium, excited in the brain by the power of the 

 will, and propagated from thence through the capil- 

 lamenta of the nerves into the muscles for contract- 

 ing and dilating them ?" And an opinion approach- 

 ing this has been adopted by some of the greatest 

 of modern physiologists; as Haller, who says 16 , that, 

 though it is more easy to find what this nervous 



15 Haller, Physiol. iv. 365. 



16 Physiol. iv. 381, lib. x. sect.viii. 15. 



