CONSTITUENTS OF ANIMALS, 



CHAPTEK VI. 



CONSTITUENTS OF ANIMALS, PLANTS, AND 

 INANIMATE MATTEE. 



Aristotle's conceptions about the constituents of 

 animals, plants, and inanimate matter were connected with 

 his views about motion. It has been stated already that he 

 believed that there was but one Kosmos or Universe, that 

 this was of spherical form, and that the Earth was at its 

 centre. He held that all motions of bodies could be resolved 

 into three simple motions : (1) rectilinear motion upwards or 

 outwards from the centre ; (2) rectilinear motion downwards 

 or inwards towards the centre, and (3) circular motion. A 

 simple body or element must have, according to Aristotle, a 

 simple motion, and, from a consideration of the motions 

 which earthy substances, water, air, and flame exhibit, he con- 

 cluded that there were four elemejits, earth, ivater, air, and Jire, 

 of which earth and loater correspond to rectilinear motion 

 towards the centre, and air and fire correspond to rectilinear 

 motion from the centre. To circular motion he assigned a 

 fifth element, cether, distinguished by being eternal and 

 indestructible, undergoing no change either in quality or 

 quantity. This element, since it could not move in a recti- 

 linear direction, either upwards or downwards, had neither 

 lightness nor heaviness. He believed that this element 

 existed in the upper regions of the Kosmos or, at any rate, 

 at some distance from us. He does not appear to have 

 considered it to be a part of terrestrial bodies.* On the 

 other hand, earth, water, air, and fire, which enter into the 

 composition of terrestrial bodies, are not eternal, and require 

 to be renewed by generation.! 



Aristotle was not the first to consider that earth, water, 

 air, and fire were the elements from which all terrestrial 

 substances are made. Empedocles, in somewhat figurative 

 language, was the first to do this, as Aristotle himself clearly 



* De Coelo, i. cc. 2 and 3, iii. cc. 3 and 5. f li^id. ii. c. 3. 



