132 CONTRACTION OF PLAIN MUSCLES. [BOOK i. 



brought to bear on a part of a fresh living still warm intestine (the 

 small intestine is the best to work with) a circular contraction is 

 seen to take place at the spot stimulated ; the intestine seems 

 nipped in ringwise, as if tied round with an invisible cord ; and the 

 part so constricted, previously vascular and red, becomes pale and 

 bloodless. The individual fibres of the circular coat in the region 

 stimulated have each become shorter, and the total effect of the 

 shortening of the multitude of fibres all having the same circular 

 disposition is to constrict or narrow the lumen or tube of the in- 

 testine. The longitudinally disposed fibres of the outer longitudinal 

 coat in a similar manner contract or shorten in a longitudinal 

 direction, but this coat being relatively much thinner than the 

 circular coat, the longitudinal contraction is altogether over- 

 shadowed by the circular contraction. A similar mode of contrac- 

 tion is also seen when the ureter is similarly stimulated. 



The contraction thus induced is preceded by a very long latent 

 period and lasts a very considerable time, in fact several seconds, 

 after which relaxation slowly takes place. We may say then that 

 over the circularly dispersed fibres of the intestine (or ureter) at 

 the spot in question there has passed a contraction-wave remarkable 

 for its long latent period and for the slowness of its development, 

 the wave being propagated from fibre to fibre. From the spot so 

 directly stimulated, the contraction may pass also 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 as 

 we have said also throw r n into contractions of altogether similar 

 character, and a wave of contraction may thus also travel longitudi- 

 nally along the longitudinal coat both upwards and downwards. 

 It is evident however that the wave of contraction of which we ai e 

 now speaking is in one respect different from the wave of contrac- 

 tion treated of in dealing with striated muscle. In the latter case 

 the contraction-wave is a simple wave propagated along the in- 

 dividual fibre and starting from the end-plate or, in the case of 

 direct stimulation, from the part of the fibre first affected by the 

 stimulus; we have no evidence that the contraction of one fibre 

 can communicate contraction to neighbouring fibres or indeed in 

 any way influence neighbouring fibres. In the case of the intestine 

 or ureter, the wave is complex, being the sum of the contraction- 

 waves of several fibres engaged in different phases and is propagate* 1 

 from fibre to fibre, both in the direction of the fibres, as when the 

 whole circumference of the intestine is engaged in the contraction, 

 or when the wave travels longitudinally along the longitudinal coat, 

 and also in a direction at right angles to the axes of the fibres, as 

 when the contraction-wave travels lengthways along the circular 

 coat of tho intestine, or when it passes across a breadth of the 

 longitudinal coat ; that is to say, the changes leading to contraction 

 are communicated not only in a direct manner across the cement 



