071 Muscular Motion and Animal Spirits 247 



the effervescence arising from the meeting of contrary 

 salts takes place only slowly, and usually lasts for some 

 time, and that this does not agree with the instan- 

 taneous contraction of the muscles, as we have indi- 

 cated above. 



So that for effecting the contraction of the muscles 

 there is required an excitement of the elastic particles, 

 of a kind that can be accomplished instantaneously 

 and without any sort of coagulation. And indeed I 

 do not know if there be in the nature of things any 

 other such fermentation but the singular case of the 

 effervescence of nitro-aerial and saline-sulphureous 

 particles, which mutually, as their nature is, excite 

 themselves to a most rapid motion. We must there- 

 fore conclude that it is from that that muscular con- 

 traction proceeds. And if the one set of motive 

 particles, as I have tried to show above, are of a saline- 

 sulphureous nature, it is most necessary that the other 

 set of motive particles should be of the nitro-aerial 

 kind, inasmuch as these alone are by their nature fitted 

 for exciting the saline-sulphureous particles. 



I think it has been established from what has been 

 elsewhere said, that nitro-aerial and sulphureous 

 particles effervesce when mixed with one another, but 

 to these evidences the following experiment may be 

 added. If, namely, the most highly rectified spirit of 

 wine be mixed with spirit of nitre deprived of its 

 moisture, a conspicuous heat will presently be pro- 

 duced, at all events if the mixture be slightly warmed ; 

 and the explanation of this seems to be that the 

 nitro-aerial particles (which we have elsewhere shown 

 to abound in the spirit of nitre) and the very volatile 

 saline-sulphureous particles of which the spirit of wine 

 consists excite one another to motion, as is their 

 nature, for it must not be supposed that the spirit of 



