58 OF VITAL MOTION. 



exposed during surgical operations; and he further 

 instances, as of similar significance, the existence of 

 certain hysteric convulsions in which all the muscles 

 are hard and expanded, so that those which (from 

 the position of the part) ought to be relaxed, are as 

 firm and unyielding as those which ought to be 

 contracted. 



In relation to the involuntary muscles the existence 

 of a twofold mode of action is very apparent, and it 

 is found that there is a power of expansion in these 

 structures altogether independent of extraneous force. 

 In some degree the contents of the viscera in whose 

 walls these muscles are seated may oppose and 

 partly counteract the state of contraction, (and in the 

 absence of all antagonist fibres in the muscles them- 

 selves, this is the only extraneous power which could 

 be productive of this result,) but any counteraction of 

 this character is more than doubtful. Be this as it 

 may, however, Bichat's arguments show that there is 

 something more than this in the relaxation of these 

 muscles. 



In the first place, this conclusion is necessary from the 

 fact, that the walls of the alimentary canal alternately 

 contract and dilate, when the contents are artificially 

 removed, or when the passage is emptied. In the 

 second place, a similar conclusion is necessary from 

 the fact, that alternate and rhythmical changes of an 

 analogous character may be observed in the heart and 



