274 On the Agency of Nerves. 



nervous system alter the irritability or contractile power of these 

 fibres. I believe we shall not commit any material error in 

 asserting, that for all useful purposes at least in the animal 

 economy, it is in the first of these ways that the volun- 

 tary muscles are affected by changes in the nervous system ; 

 and in the second, that the involuntary muscles are affected by 

 such changes ; and it would appear, from the passages quoted 

 from Haller, that this was his opinion in regard to the uses of 

 the nerves of the two sets of muscles. But the farther prosecu- 

 tion of this curious subject would be foreign to the purpose of 

 this paper. 



3. The main objects of my former paper were, Jirst, to shew 

 that Dr. Philip's conclusion, in regard to the dependence of se- 

 cretion on an influence derived from the nerves, did not necessa- 

 rily follow from his premises; and, secondly, to state various consi- 

 derations, which I had not seen fully stated by others, which seem 

 to me to render that conclusion very improbable. The argu- 

 ment on the first head may be recapitulated in a very few words. 



Dr. Philip distinctly proved, that although the actions of 

 the heart may be totally suspended by crushing, either the spinal 

 marrow, as in Le Gallois's experiments, or the brain, yet these 

 actions are perfectly independent both of the brain and spinal 

 marrow, and may go on, although both are removed from the 

 body. Hence, those lesions of the nervous system are no proof 

 that the actions of the heart depend on, or are derived from, 

 the brain or spinal marrow. Several experimenters have found, 

 that another lesion of the nervous system, cutting the eighth 

 pair of nerves, materially alters the secretion of the stomach. 

 When Dr. Philip inferred from this, that the secretion of the 

 stomach is necessarily dependent on the nervous system, he 

 seemed to me to have fallen into the very same error that he 

 had pointed out in Le Gallois ; because, as we are perfectly 

 ignorant how any lesion of the nervous system affects either 

 muscular action or secretion, it is just as possible, for any thing 

 we know to the contrary, that secretion, although independent 

 of nerves, may be altered or suppressed by cutting nerves, as 



