1818.] the Nature of the Vital Ppwers. 115 



These objections to the opinion of this great physiologist 

 appear to be removed by the 23d experiment related in the above- 

 mentioned Inquiry, from which it appears that the nervous 

 influence acts only as a stimulus on the muscular fibre, and 

 exhausts its power as other stimuli do ; and by a great variety of 

 experiments related in that Inquiry, which seem to prove that 

 the muscular power is not destroyed, in the cases just alluded 

 to, in consequence of the loss of power in the nervous system, 

 but in consequence of the cause of injury acting on the muscular 

 fibre through that system ; for it appears from them, that the 

 nervous power may be as effectually destroyed by other means, 

 without at all impairing the power of the muscular fibre. If it 

 be allowed that the experiments here referred to remove the fore- 

 going objections to the opinion of Haller, this opinion must be 

 allowed to be a legitimate inference from experiment ; no other 

 objections to it, 1 believe, having been regarded as of weight. 

 The power of the muscular fibre then is a property depending on 

 the mechanism of that fibre, and in no degree directly dependent 

 on the nervous system. 



That the nervous is independent of the muscular power has not 

 been questioned ; but the sensorial and nervous powers have 

 never been correctly distinguished. As far as I know, M. le 

 Gallois is the only author who has attempted, by experiments, 

 to establish a distinction between them. 1 have, in the above- 

 mentioned Inquiry, stated my reasons for not adopting the line 

 of distinction pointed out by this writer, and endeavoured, by 

 many experiments, to ascertain where this line lies. From these 

 experiments it appears, that the functions of the nervous influence 

 are those of stimulating the muscles both of voluntary and invo- 

 luntary motion, conveying impressions to and from the senso- 

 rium, affecting the formation of the secreted fluids, and causing 

 ■an evolution of caloric from the blood ; and that we have reason 

 to believe it capable of all these functions after the sensorial 

 power is withdrawn, that is, after the animal is no longer capable 

 of perception or any act of volition, and is consequently, in the 

 common sense of the term, dead. 



Nobody has supposed that the sensorial power has any direct 

 dependance on the muscular and nervous power. 



I f the foregoing observations be correct, each of these powers 

 lias an existence not directly depending on the others. My 

 object in the remaining part of this letter, is to inquire how far 

 we are acquainted with the causes which produce the phenomena 

 of these different powers. 



When we say that we are acquainted with the cause of any 

 particular set of phenomena, we only mean that we know them to 

 .irise from the same cause which produces other more familiar 

 phenomena. Thus we are acquainted with the cause which 

 retains the planets in their dibits, because Sir Isaac Newton 

 I roved it to be the same' which produces the other phenomena of 



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