OF VITAL MOTION. 49 



the he.art be substituted for the syringe, and we may 

 suppose that the blood moves sluggishly when the 

 vessels are contracted, and rapidly when this cause of 

 resistance is overcome, and the calibre expanded, and 

 that the so-called capillary power is directed to the 

 removal of impediments to the action of the heart, 

 and not an inherent heart-like faculty of action. 



II. OF THE CELLULAR MOVEMENTS IN ANIMAL 

 BODIES. 



Great attention has been paid to the anatomical 

 peculiarities of cells, and to their modes of growth, but 

 this has been almost altogether without reference to 

 efficient causes. Indeed, in this case, as in many 

 others in physiology, these important considerations 

 have been neglected on the ground that they referred 

 to some principle whose operations were in no degree 

 cognisable to the reason. 



On comparing, however, the analogous sections in 

 the history of the plant and the animal, we find many 

 reasons to suppose that the cells in each case are acted 

 upon by the same agents, and in the same manner. 

 In the animal, external warmth is necessary to growth, 

 as is evident from the history of nutrition in hyber- 

 nating animals, for in them the process of growth is 

 arrested during winter. Light, also, is necessary, as 

 we may see particularly in the effects of this agent in 

 determining the free development of the blood and the 







