

SMOOTH MUSCLES. 



the electro-motor force, elasticity, and respiratory exchanges 

 (combustion). But what distinguishes the smooth muscle from 

 the striated muscle is that in the former the passage from 

 the first to the second form is made with extreme slowness. 

 After the excitation which irritates the fibre, and gives rise 

 to its change of form, a considerable time always elapses 

 before the change occurs. As this latent excitation lasts a 

 long time, so the contraction which follows is produced very 

 slowly, continues for some time at its height, and then grad- 

 ually relaxes. 



Thus, the only consequence of the difference in structure 

 of the smooth muscles is that they yield less readily to the 

 influence of irritants, and contract more slowly than the 

 other muscles. They also pass into the state of cadaveric 

 rigidity in the same manner as the striated muscles. A state 

 of transition between the striated muscles and the smooth 

 muscles, properly so called, is also sometimes observed. This 

 is the case, up to a certain point, with the muscular tissue of 

 the heart. (See p. 86.) 



On resuming a series of investigations as to the compara- 

 tive physiology of the smooth and the striated muscles, M. 

 Legros and M. Onimus arrived at the following conclusions : 

 in the case of the striated muscles both the contraction and 

 the return to a state of repose are rapid, while in that of the 

 smooth muscles both are slow. These movements are always 

 involuntary. The contraction (physiological tetanus) of the 

 former is caused by a series of shocks, while that of the lat- 

 ter conies on gradually, without oscillation. The peristaltic 

 form (see intestine) is that in which these contractions most 

 frequently appear. The motility (excitability) lasts longest 

 in the smooth muscles after death. In the striated muscles 

 electrical excitation of the motor nerves of the muscle pro- 

 duces more effect than that of the muscle itself; with the 

 smooth element the reverse is the case. Finally, if the two 

 poles of an induced current be made to act upon the smooth 

 muscles, by placing these poles at a certain distance from 

 each other, we find, in the intestinal tube, for instance, that 

 instead of the whole muscle contracting, those parts only 

 contract which come in contact with the poles ; in the inter- 

 mediate parts there is no contraction, but rather relaxation. 

 The effect produced by continuous currents is still more 

 remarkable: in those organs which have peristaltic move- 

 ments (see intestine ; vaso-motors) there are variations cor- 

 responding with the direction of the current; when this 



