SEC. 7. OTHER FORMS OF CONTRACTILE TISSUE. 



Unstriated Muscular Tissue. Our knowledge of the phenomena 

 of these structures is very imperfect since (in vertebrates) they do 

 not exist in isolated masses like the striated muscles, but occur as 

 constituents of complex organs, such as the intestine, ureter, 

 uterus, &c. They undergo rigor mortis : and what little informa- 

 tion we do possess concerning their chemical and physical features 

 leads us to believe that the processes which take place in them are 

 fundamentally identical with those occurring in striated muscle, 

 the two differing in degree rather than in kind. When stimulated, 

 they contract. If a stimulus, mechanical or electrical, be applied 

 to the intestine or ureter of a mammal, a circular contraction is 

 seen to take place at the spot stimulated. The contraction, which 

 is preceded by a very long latent period, lasts a very considerable 

 time, in fact several seconds, after which relaxation slowly takes 

 place. That is to say, over the circularly dispersed fibres of the 

 intestine (or ureter) at the spot in question there has passed a con- 

 traction-wave remarkable for its long latent period and for the slow- 

 ness of its development. From the spot so directly stimulated, the 

 contraction may pass as a wave (with a length of 1 cm. and a 

 velocity of from 20 to 30 millimetres a second in the ureter), along 

 the circular coat both upwards and downwards. The longitudinal 

 fibres at the spot stimulated are also thrown into contractions of 

 altogether similar character, and a wave of contraction may also 

 travel longitudinally along the longitudinal coat both upwards and 

 down wards. It is evident however that the wave of contraction of 

 which we are now speaking is in one respect different from the 

 wave of contraction treated of in dealing with striated muscle. In 

 the latter case the contraction-wave is a simple wave propagated 



