THE FUNCTIONS OP LIFE. 41 



gratification, and reject those which are useless or hurtful, 

 but may always move from place to place, and enlarge the 

 sphere of its perceptions and of its power. The same mass 

 of nervous substance which, under the name of brain, we 

 have recognised as the organ of sensation, is also, as will af- 

 terwards be shown, the organ of volition; and the medium, 

 by which the commands of the will are transmitted from 

 the brain to the mechanical apparatus employed for motion, 

 is again certain filaments of nerves; but these nervous fila- 

 ments are distinct from those which are subservient to sen- 

 sation. 



Next in importance, then, to the organs of sensation and 

 perception, are those of Voluntary Motion. They com- 

 prise two kinds of objects; first, the establishment of a cer- 

 tain mechanism having the cohesion, the strength, and the 

 mobility requisite for the different actions which the animal 

 is to perform; and, secondly, the provision of a power, or 

 agent, which shall be capable of supplying the mechanical 

 force for setting this machinery in motion. With these ob- 

 jects must be combined various subsidiary arrangements re- 

 lating to the connexions, the support, the protection, and 

 other mechanical conditions of the organs of the body. It will 

 be convenient to comprehend these under one general head, 

 considering them as composing the Mechanical Functions 

 of the animal economy. They will engage a considerable 

 share of our attention in this work, as afibrding the clearest 

 and most palpable proofs of contrivance and design. 



From the peculiar conditions of the living body, not only 

 with regard to the mechanical properties of its various parts, 

 and the powers by which their movements are effected, but 

 also with regard to the chemical laws which regulate the 

 combinations of elements composing the substance of the 

 body, there is required, as will be more fully explained in 

 the sequel, a continual renovation of that substance. For 

 this purpose new materials are perpetually wanted, and must 

 be as regularly supplied. Hence arises a new class of func- 

 tions, comprising a great extent of operations, opening a wide 

 Vol. I. 6 



