FUNCTIONS OF MUSCULAR TISSUE. 319 



Heart only excepted), they produce a simultaneous contraction in the whole 

 muscle ; the effect of the stimulus being at once exerted upon every part of it. 

 The contraction speedily alternates with relaxation, unless the operation of the 

 stimulus be continued as when an electric current is propagated without inter- 

 mission along the nerve-trunks in which case the contraction lasts as long as 

 the stimulus is continuously applied, but ceases as soon as it is withdrawn. Eut 

 it has been shown by Volkmann, 1 that, if the electric stimulus be applied to the 

 central organs from which the motor nerves arise, the muscular contraction con- 

 tinues for some time after its withdrawal. Further, he found that when the 

 continuous electric current was passed through incident or excitor nerves, it 

 produced alternating movements of contraction and relaxation, 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. Abundant evidence that they are thus 

 excitable, however, although the excitability speedily ceases after death, will be 

 given hereafter (CHAP. xiv. SECT. 6). The results of Volkmann' s recent elec- 

 trical experiments upon the Heart and the Intestinal 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 contractions 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 Sympathetic system. When the Heart is removed from the body, 

 and is left entire, 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. 2 These experiments, hpwever, by no means 

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

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

 variety of evidence. 



318. The general fact, that Muscular contraction alternates with relaxation 

 at no long intervals, is most evident in the rhythmical movements of the Heart, 3 

 and in the peristaltic action of the Intestinal Canal ; since, in these 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 ( 303), 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 



1 "Muller's Archiv.," 1844, No. 5, p. 407. 



2 Op. cit. ; and Mr. Paget's "Report" for 1845, in "Brit, and For. Med. Rev.," July, 

 1846. 



3 Some curious rhythmical movements have been observed by M. Brown-Sequard, in the 

 diaphragm, intercostals, and some of the muscles of locomotion, both after death, and after 

 section of their nerves during life. These movements could not be in any way dependent 

 upon reflex action, because they took place when the muscles were completely cut oif from 

 the nervous centres ; sometimes to the number of from 5 to 20 in a minute, and for as long 

 as a quarter of an hour after death ; and occasionally recurring, in a living animal, for 

 many months afterwards, especially when the respiration was impeded, and the circulation 

 hurried. The fact is of much importance, as showing that the rhythmical movements of 

 the heart are by no means so exceptional (among the muscles composed of striated fibre) 

 as they are usually accounted ; and also that there is a tendency to rhythmical movement 

 in the muscles themselves, altogether independent of the excitement to action which they 

 receive through the nervous system. ("Gazette Medicale," Dec. 22, 1849.) 



