4 ZOOLOGY. 



force ; their duration is not limited ; they are not necessarily 

 destructible : but I repeat all that lives is sure to perish ; 

 and thus, were it not for the faculty of reproduction, not 

 bestowed on minerals, life under every form would soon dis- 

 appear from the earth. 



7. As regards form and size, or volume, we find that 

 living bodies are destined to acquire a certain size and form, 

 gradually and by development, which they did not possess at 

 birth. The form has no geometrical simplicity ; with mine- 

 rals it is quite otherwise. The smallest fragment of marble 

 is as much marble as the largest mass which can be'imagined ; 

 but a plant or animal can only live by attaining a certain 

 dimension, beyond which it cannot grow. Neither can they 

 be divided into fragments, like minerals, and yet exist as indi- 

 viduals ; a term which is chiefly applied only to organized 

 beings. When mutilated beyond a certain point, they cease 

 to exist. 



8. The intimate structure of living bodies furnishes other 

 characters. They are always composed of fluids and solids, 

 the former being enclosed in cells formed by plates, lamina?, 

 or filaments. It is this structure to which the name of 

 organization has been given. Nothing of the kind is to be 

 seen in the mineral kingdom. A spongy and areolar texture, 

 into which liquids may readily penetrate, is, then, a necessary 

 condition for the existence of life, whether animal or vege- 

 table ; and hence the name of organized beings, as opposed 

 to minerals, which receive the name of inorganic bodies. 



9. Lastly, the distinction between the two great divisions 

 of natural bodies, the organic and inorganic, extends even to 

 their elementary or chemical composition. 



A mineral body may be formed of molecules strictly of one 

 kind, as sulphur or iron ; or may resultjrom the union of two 

 or more chemical elements, the number" of which exceeds fifty. 



With living beings it is different : their chemical composi- 

 tion is always most complex, and in order to render this clear, 

 the constituent elements of such beings have been arranged 

 under three heads or classes. 1. Those which, like water 

 and various salts, present nothing peculiar, and belong to 

 the inorganic bodies. 2. Organic matters, such as sugar, 

 and urea, which are formed under the influence of life. 

 3. The plastic and viable products, as albumen, fibrin, cellulose, 

 which possess chemical characters of high importance. Into the 

 composition of these there always enter three sometimes four 



