296 Royal Society. 



otherwise paralysed ? and if a muscle contracts for want of blood, 

 how is it that it relaxes in syncope, asphyxia, and death ? These 

 objections are grave, but not ^insurmountable, as the following hints 

 at explanation will serve to show. 



It must be understood, then, that that state of polar action which 

 is present in a muscle during rest and absent during contraction, is 

 re-established immediately after contraction; it must also be under- 

 stood that this state of polar action in the muscle is suspended 

 during ordinary muscular contraction by certain changes which take 

 place in the nervous centre, and that it has died out when contrac- 

 tion happens after death, as in rigor mortis ; and the rest is suffi- 

 ciently simple. 



It is quite in accordance with the theory, then, that a muscle 

 should contract when nervous influence is withdrawn, and that it 

 should relax after the nerve is divided or otherwise paralysed. At 

 the moment when the continuity of the nerve is broken the muscle 

 contracts, because the influence of the nervous centre is cut off; 

 but this contraction cannot continue, because that state of polar 

 action which antagonizes contraction is immediately re-established 

 in the muscle, and in the portion of nerve connected with it. This 

 relaxation, moreover, must continue, if the paralysed muscle be left 

 to itself, so long as the muscle continues to be the seat of this polar 

 action. And, on the other hand, this contraction must return when 

 this action is suspended, or diminished, or extinguished, as indeed 

 it does ; thus the muscle contracts when the polar action is sud- 

 denly suspended by galvanism or by the touch of a needle ; thus it 

 contracts after the paralysis has continued for some time, and when 

 the failure in the nutrition of the muscle has entailed a correspond- 

 ing failure in its polar action ; and thus it contracts in rigor mortis, 

 when all polar action is finally extinguished. 



It is also in accordance with theory that tremor, convulsion, and 

 spasm should be caused by want of blood, and that they should 

 cease when the circulation fails, as it fails in syncope, asphyxia, or 

 death. During tremor, convulsion, or spasm, the muscles are insuffi- 

 ciently supplied with nervous influence, because the deficient supply 

 of blood to the nervous centres involves a corresponding deficiency in 

 the degree of innervation ; but once let the circulation fail below a 

 certain point, and the whole case is altered. During tremor, con- 

 vulsion, and spasm, the supply of blood to the nervous centres is in- 

 sufficient to keep up the normal degree of innervation, but it is suffi- 

 cient to prevent the nerves from being paralysed, and hence the con- 

 tractions in the muscles, for the nerves being conductors, the failure 

 in the action of the nervous centres is propagated along them to the 

 muscles, and of this failure the contractions are the consequence. 

 But if the circulation fails below a certain point, the nerves are 

 paralysed for want of blood, and being paralysed, the failure of in- 

 nervation in the nervous centres, even though this be now complete, 

 does not entail a corresponding failure in the polar action of the 

 muscle, because the nerves are no longer conductors ; and not 

 doing this, the polar action of the muscle, which is much more 



