THE TISSUES 71 



1. Their connection with nerves is by no means so definite 

 and precise, for, instead of each nerve-fibre ending in a muscle- 

 fibre, the nerves to non-striped muscle form an irregular 

 network upon them, and the muscle-fibre appears to be capable 

 of action, possibly before these nerves have developed in the 

 embryo and when the influence of these nerves has been cut 

 off in the adult. In the intestine the mode of action of the 

 muscles is largely dominated by the plexus of nerves (see 

 p. 385). 



2. The great features of the action of visceral muscle are 

 1st, its tendency to sustained tonic contraction ; and 2nd, 



its spontaneous regular rhythmic contraction and relaxation. 



1st. The continuous slight tonic contraction is seen in all the 

 visceral muscles ; and, while it may be increased or diminished 

 by the intervention of nerves, it appears to be chiefly an 

 expression of the continuous metabolism of the muscle proto- 

 plasm. 



2nd. The rhythmic contractions and relaxations are not 

 equally manifest in all situations, nor are they so continuous ; 

 but they are well marked in the muscles around such hollow 

 viscera as the intestines, bladder, and uterus. Like the tonic 

 contractions, they are to a certain extent independent of nerve 

 action, but are influenced by it. 



These contractions recur at regular intervals of varying 

 duration. Each contraction lasts for a considerable period 

 sometimes over a minute and the relaxation is correspond- 

 ingly long. Everything which increases the rate of chemical 

 change increases the rapidity of the rhythm. Thus warming 

 the muscle and the action of a galvanic current have this 

 action. 



3. When the muscle is at rest, a contraction may be pro- 

 duced by any of the modes of stimulation which will cause 

 the skeletal muscles to contract; and it may thus be demon- 

 strated that the latent period is very long. 



4. Unlike skeletal muscles, the extent of contraction is 

 not increased by increasing the strength of the stimulus. 

 The smallest available stimulus causes the maximum con- 

 traction; but if the same stimulus is repeated at regular 

 intervals the resulting contractions become greater and 

 greater during the application of the first four or five stimuli, 



