464 MOTION. 



more slowly, extends beyond the part irritated, and with alter- 

 nating relaxation, continues for some time after the withdrawal 

 of the irritation. Ed. Weber particularly illustrated the dif- 

 ference in the modes of contraction of the two kinds of mus- 

 cular fibres by the effects of the electro-magnetic stimulus. 

 The rapidly succeeding shocks given by this means to the 

 nerves of muscles excite in all the transversely-striated muscles 

 a fixed state of tetanic contraction, which lasts as long as the 

 stimulus is continued, and on its withdrawal instantly ceases : 

 but in the muscles with smooth fibres they excite, if any move- 

 ment, only one that ensues slowly, is comparatively slight, 

 alternates with rest, and continues for a time after the stim- 

 ulus is withdrawn. 



In their mode of responding to these stimuli, all the volun- 

 tary muscles, or those with transverse striae, are alike; but 

 among those with plain or unstriped fibres there are many dif- 

 ferences a fact which tends to confirm the opinion that their 

 peculiarity depends as well on their connection with nerves 

 and ganglia as on their own properties. According to Weber, 

 the ureters and gall-bladder are the parts least excited by 

 stimuli ; they do not act at all till the stimulus has been long 

 applied, aud then contract feebly, and to a small extent. The 

 contractions of the caecum and stomach are quicker and wider- 

 spread ; still quicker those of the iris, and of the urinary 

 bladder, if it be not too full. The actions of the small and 

 large intestines, of the vas deferens, and pregnant uterus, are 

 yet more vivid, more regular, and more sustained ; and they 

 require no more stimulus than that of the air to excite them. 

 The heart is the quickest and most vigorous of all the muscles 

 of organic life in contracting upon irritation, and appears in 

 this as in nearly all other respects, to be the connecting mem- 

 ber of the two classes of muscles. 



All the muscles retain their property of contracting under 

 the influence of stimuli applied to them or to their nerves for 

 some time after death, the period being longer in cold-blooded 

 than in warm-blooded Vertebrata, and shorter in birds than 

 in Mammalia. It would seem as if the more active the respi- 

 ratory process in the living animal, the shorter is the time of 

 duration of the irritability in the muscles after death ; and 

 this is confirmed by the comparison of different species in the 

 same order of Vertebrata. But the period during which this 

 irritability lasts, is not the same in all persons, nor in all the 

 muscles of the same persons. In a man it ceases, according 

 to Nysten, in the following order : First in the left ventricle, 

 then in the intestines and stomach, the urinary bladder, right 

 ventricle, oesophagus, iris ; then in the voluntary muscles of the 



