General Principles of Physiology. 109 



also find, applies to the blood-vessels. The motions of the 

 alimentary canal also, we have seen, are uninfluenced by the 

 removal of the brain and spinal marrow ; yet we see them in- 

 fluenced by affections of the mind, and cannot doubt that this 

 admits of the same explanation with the influence of these 

 affections on the heart, namely, the direct influence of the 

 nerves on their muscular fibres. 



The foregoing facts afford an easy solution of the difficulties 

 stated in the report of the Committee of the Royal Academy of 

 Sciences. The heart continues to act for some time after it is 

 removed from the body, and performs its functions in the foetal 

 state, when no brain, and, as the committee ought to have added, 

 no spinal marrow has existed, because it has no direct dependence 

 on any part of the nervous system. The heart is supplied with 

 nerves, and subject to the influence of the passions, because, al- 

 though independent of this system, it is capable of being influ- 

 enced through it. 



Precisely the same laws obtain, with respect to the muscles 

 of voluntary motion. It appears, from the experiment just 

 referred to, that their power is equally independent of the 

 nervous system, and constant experience proves that they 

 are under its immediate influence. 



In other respects, however, the laws which the muscles of 

 voluntary, and those of involuntary, motion obey are different. 

 It appears, from what has been said, that the two sets of muscles 

 differ in the nervous influence being the sole stimulus of the 

 former, while the latter, in all their usual functions, are each 

 excited by its peculiar stimulus, that influence only occa- 

 sionally affecting them. We shall also find them differing in the 

 manner in which the nervous influence is supplied to them. But 

 to say more here would too much anticipate that part of the sub- 

 ject which we are next to consider. 



Much has been said of the cause of the one set of muscles 

 being subjected to the will, while the other is independent of 

 it; but if the mind be freed from preconceptions, we can surely 

 be at no loss to account for this difference, when we know that 

 the muscles of involuntary motion arc all exposed to the con- 



