592 MOTION. 



irritated, the subsequent contraction ensues more slowly, 

 extends beyond the part irritated, and with alternating 

 relaxation, continues for some time after the withdrawal 

 of the irritation. Ed. Weber particularly illustrated the 

 difference in the modes of contraction of the two kinds of 

 muscular 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 trans- 

 versely-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 movement, only one that 

 ensues slowly, is comparatively slight, alternates with rest, 

 and continues for a time after the stimulus is withdrawn. 



In their mode of responding to these stimuli, all the 

 voluntary muscles, or those with transverse striae, are 

 alike; but among those with plain or unstriped fibres 

 there are many differences, 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, and then 

 contract feebly, and to a small extent. The contractions 

 of the csecum 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 member of the two classes of muscles. 



All the muscles retain their property of contracting un- 

 der the influence of stimuli applied to them or to their 



