440 OF MUSCULAR CONTRACTION. 



long as the stimulus is continuously applied, but ceases as soon as it is with- 

 drawn. But it has been lately stated by Volkmann,* that, if the electric 

 stimulus be applied to the central organs, from which the motor nerves arise, 

 the muscular contraction continues for some time after its renewal. If this 

 should prove to be a universal fact, it will afford a valuable means of distin- 

 guishing what are the real centres of the motor nerves of particular organs. 

 Further, when the continuous electric current was passed through incident or 

 excitor nerves, it produced alternating movements of contraction and relaxa- 

 tion, in the muscles which were thus called into play by reflex stimulation. 

 The ordinary actions of the non-striated fibre, on the other hand, are not 

 easily excitable by stimuli applied to their nerves ; indeed many Physiologists 

 have denied the possibility of producing them through this channel. Positive 

 evidence to this effeflt, however, has been already given ( 388). The results 

 of Volkmann's recent electrical experiments upon the Heart and the Intesti- 

 nal Canal are of much interest. He found that neither of these organs is 

 thrown into fixed contraction, when the continuous electric current is applied 

 to the Brain and Spinal Cord ; whence he concludes that these organs are not 

 the centres of their motor nerves. On the other hand, alternating contrac- 

 tions and relaxations were produced on applying the continuous current to 

 the spinal cord, the par vagum, and the sympathetic nerves ; whence it may 

 be concluded that these parts contain afferent fibres, which excite motion 

 through centres that can scarcely be any others than the ganglia of the Sym- 

 pathetic system. When the Heart is removed from the body, and is left en- 

 tire, it may be thrown into a state of fixed contraction, which lasts after the 

 cessation of the current; whence it may be concluded, that it contains the 

 centre of its own motor nerves.t These experiments, however, by no means 

 warrant the conclusion, that the ordinary actions of these muscular organs are 

 dependent upon the agency of their nerves ; which is opposed by a variety of 

 evidence. 



577. The general fact, that Muscular Contraction alternates with Relaxa- 

 tion at no longer intervals, is most evident in the rhythmical movements of 

 the Heart, and in the peristaltic action of the Intestinal canal ; since in those 

 parts, the whole or a large proportion of the fibres seem to contract together, 

 and then shortly relax. But it is probably no less true, as formerly stated 

 ( 232), of the individual fibres of those muscles, which are kept in a state 

 of contraction by a stimulus transmitted through their nerves; since none of 

 them appear, under ordinary circumstances at least, to remain in a contracted 

 state for any length of time, a constant interchange of condition taking place 

 among the fibres, some contracting whilst others are relaxing, and vice versa. 

 It is difficult to speak with confidence, however, in regard to the condition of 

 the individual fibres of a muscle, that is thrown into a state of continued 

 spasmodic contraction ; such as that produced by the application of the elec- 

 tric current to the centre of its motor nerves ( 576). A state of this kind is 

 often of considerable duration. Thus the Author has known a case of Hys- 

 teric Trismus, in which the jaws remained closed with the greatest violence 

 during five days. Whether the individual fibres, in such instances, maintain 

 a state of contraction without intermission, or whether the contraction of the 

 entire muscle is kept up by a continual interchange of the fibres actually en- 

 gaged, is a very curious subject for inquiry. 



578. Muscles do not lose their Irritability immediately on the general 

 death of the system, which must be considered as taking place, when the cir- 

 culation ceases without a power of renewal ; in cold-blooded animals it is re- 



* Muller's Arcbiv., 1844, No. 5, p. 407. 



t Op. cit.; and Mr. Paget's Report for 1845, in Brit, and For. Med. Rev., July, 1S4U. 



