56 OF VITAL MOTION. 



Under any circumstances the general phenomena 

 of motion in plants conform to the law which rules in 

 the sensitive plant, and as to the rest, it may be 

 doubted whether there are any exceptional cases that 

 are truly so. 



2. Of intra- organic force as the agent in these 

 movements. 



Of these agents we have little knowledge, but there 

 is reason to believe from the history of other move- 

 ments of the plant, with which we have already been 

 occupied, that they are of comparatively trifling 

 importance. At present, indeed, we must be content 

 to understand that the agency of extra-organic force 

 is sufficient to account, in some measure at least, for 

 the phenomena under consideration, and we must 

 leave the darker and more mysterious operations of 

 vitality until we can study the clearer manifestations 

 which occur in animal bodies. 



Section II. 



OF VITAL MOVEMENTS SUCH AS ARE SEEN IN THE 

 COATS OF THE ALIMENTARY CANAL, AND IN VOLUN- 

 TARY MUSCLES. 



Preliminary Considerations. 

 In relation to these phenomena there are two initial 

 considerations which demand our attention. The 

 first is, that all modes and forms of the contractile 



