20 OF VITAL MOTION. 



the dilated centres, for these contents may be supposed 

 to be impoverished by having subserved to the nutri- 

 tive wants of the part, and to have become on this 

 account far less fitted to the performance of those 

 molecular changes which originate heat : and hence 

 the stage of contraction may be in part due to a 

 direct diminution of the local manifestation of organic 

 heat. 



Other agencies, without doubt, have some share in 

 the determination of these phenomena, as we shall see 

 in the sequel ; but in the operation of heat, we find 

 as it seems the first step in the explanation of the 

 primary absorption of the latex into the contracted 

 vessels, and of the subsequent oscillation of this fluid 

 to and from certain focal centres, while at the same 

 time we are able to account, by the same means, for 

 the change of position in the centres themselves. 



II. OF THE MOVEMENTS IN SIMPLE CELLS, AND 

 THE PHENOMENA OF " ROTATION." 



1. Of extra-organic force as the agent in these 

 movemnts. 



The functions of the laticiferous vessel and the 

 common cell are called into action at the same time, 

 and the season which determines or suspends the 

 vascular changes determines and suspends also the 

 growth and internal movements of the cell. 



