5*20 HANDBOOK OF PHYSIOLOGY. 



qnent contraction ensues more slowly, extends beyond the part irritated, 

 and, with alternating relaxation, continues for some time after the 

 withdrawal of the irritation. The difference in the modes of contrac- 

 tion of the two kinds of muscular fibres may be particularly illustrated 

 by the effects of the repeated stimuli with the magnetic interrupter. 



Fig. 888. Muscle-curves from the gastrocnemius of a frog, illustrating effects of alterations in 



temperature. 



The rapidly succeeding shocks given by this means to the nerves of mus- 

 cles excite in all the transversely striated muscles, except in the case of 

 the heart, a fixed state of tetanic contraction as previously described, 

 which lasts as long as the stimulus is continued, and on its withdrawal 

 instantly ceases; but in the muscles with nnstriped fibres they excite a 

 slow vermicular movement, which is comparatively slight and alternates 

 with rest. It continues for a time after the stimulus is withdrawn. 



In their mode of responding to these stimuli, all the skeletal muscles, or 

 those with transverse striae, are alike ; but among those with 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. The ureters and gall-bladder are the parts least 

 excited by stimuli ; they do not act at all till the stimulus lias been long applied, 

 and then contract feebly, and to a small extent. The contractions of the cascum 

 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, on account, doubtless, of its striated muscle, 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 con- 

 necting member 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 Vertebrate,, and shorter in 

 Birds than in Mammalia. It would seem as if the more active the respiratory 

 process in the living animal, the shorter is the time of duration of the irrita- 

 bility 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 person. 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 mus- 

 cles of the trunk, lower and upper extremities ; lastly, in tba right and left 

 auricle of the heart. 



