POWERS OF ASSIMILATION. 17 



the removal of these useless or noxious materials, by trans- 

 ferring them to the general mass of circulating blood, so as 

 either to be again usefully employed, or altogether discard- 

 ed by excretion from the system. This object is accom- 

 plished by a peculiar set of vessels; and the function they 

 perform is termed Absorption. 



Lastly, the conversion of the fluid nutriment into the 

 solids of the body, and its immediate application to the 

 purposes of the development of the organs, of their preser- 

 vation in the state of health and activity, and of the repair 

 of such injuries as they may chance to sustain, as far as the 

 powers of the system are adequate to such reparation, are 

 the objects of a seventh set of functions, more especially 

 comprised under the title of Nutrition, which closes this 

 long series of chemical changes, and this intricate but har- 

 monious system of operations. 



Although the order in which the constituent elements of 

 organized products are arranged, and the mode in which 

 they are combined, are entirely unknown to us, we can ne- 

 vertheless perceive that in following them successively from, 

 the simplest vegetables to the higher orders of the animal 

 kingdom, they acquire continually increasing degrees of 

 complexity, corresponding, in some measure, to the greater 

 refinement and complication of the structures by which they 

 have been elaborated, and of the bodies to which they are 

 ultimately assimilated. Thus, plants derive their nourish- 

 ment from the crude and simple materials which they ab- 

 sorb from the earth, the waters, and the air that surround 

 them; materials which consist almost wholly of water, with 

 a small proportion of carbonic acid, and a few saline ingre- 

 dients, of which that water is the vehicle. But these, after 

 having been converted by the powers of vegetable assimila- 

 tion, into the substance of the plant, acquire the character- 

 istic properties of organized products, though they are still 

 the simplest of that class. In this state, and when the fabric 

 they had composed is destroyed, and they are scattered 

 over the soil, they are fitted to become more highly nutri- 



VOL. II. 3 



