OF VITAL MOTION. 15 



which this physical agent may be concerned in these 

 changes ; and to this end, let us divest ourselves of 

 those ideas of mysterious and unknown powers with 

 which the explanation is presumed to be connected, 

 and at the same time banish the notion that the 

 causes of vital movement ??22/5^, of necessity, be different 

 from those which determine motion in inanimate 

 bodies, while we consider, on ordinary principles, 

 the necessary effects of heat under these circum- 

 stances. 



Motion is one of the effects of heat in ordinary 

 matter, repulsion of the particles marking the com- 

 munication, and attraction the withdrawal, of the 

 influence. If the body acted upon be arranged in a 

 tubular form, an alteration in the capacity of the 

 cavity must result, the calibre being diminished or 

 extended, as the case may be. Such, also, may be 

 presumed to be the effect of heat in a vessel composed 

 of the simpler organic fabrics, for we have already 

 seen that the particles of these tissues are affected 

 like those of inorganic bodies. 



Let it be supposed, then, that a latex vessel is acted 

 upon by heat, and what, we may ask, will be the con- 

 sequences. The vessel, as we have already seen, is 

 composed of matter possessed of a remarkable sus- 

 ceptibility to movement under slight alterations of 

 heat, much greater in degree than that which belongs 

 to water, or blood, or the allied fluids, and therefore 



