2 MANUAL OF ZOOLOG-T. 



ised bodies seriatim, and to compare them together system- 

 atically under the following heads : 



a. Chemical composition. Inorganic bodies are composed 

 of many elements, which may be either simple or combined ; 

 but the combinations are limited to a small number of ele- 

 ments (forming binary and ternary compounds), and these 

 are united in low combining proportions. Thus carbonate of 

 lime, or common limestone, is an excellent example of an in- 

 organic body,* being a ternary compound composed of one 

 atom of the metal calcium, three of oxygen, and one of carbon. 



Organised bodies, on the other hand, are composed of few 

 chemical elements, and these are almost always combined. 

 Furthermore, the combinations are always complex (ternary 

 and quaternary compounds), and the elements enter into union 

 in high combining proportions. Finally, the combinations are 

 invariably characterised by the presence of water, and are prone 

 to spontaneous decomposition. Thus, the great organic com- 

 pound, albumen, is composed of 144 atoms of carbon, 110 

 of hydrogen, 18 of nitrogen, '2 atoms of sulphur, and 42 of 

 oxygen. Iron, however, exists in the blood, very probably in 

 its elemental condition, and copper has been detected in the 

 liver of certain mammalia, and largely in the red colouring- 

 matter of the feathers of certain birds. 



6. Arrangement of Parts. Unorganised bodies are composed 

 of an aggregation of homogeneous parts (when unmixed) which 

 bear no definite and fixed relations to one another. 



Organised bodies are composed of heterogeneous parts, the 

 relations of which amongst themselves are more or less definite. 



c. Form. Unorganised bodies are either of no definite shape 

 when they are said to be ' amorphous ' or they are crystal- 

 line, in which case they are almost invariably bounded by 

 plane surfaces and straight lines. Organised bodies are always 

 more or less definite in shape, presenting convex and concave 

 surfaces, and being bounded by curved lines. 



d. Mode of Increase. When unorganised bodies increase in 

 size, as crystals do, the increase is produced simply by what is 

 called 'accretion,' that is to. say, by the addition of fresh 

 particles from the outside. . 



Organised bodies increase by what is often called the ' in- 

 tussusception ' of matter ; in other words, by the reception of 

 matter into their interior and its assimilation there. To this 

 process alone can the term ' growth ' be properly applied. 



e. Cyclical Change. Inorganic bodies exhibit no actions that 



* In another sense limestone may be said to be organic, namely, when 

 it has been produced by the operations of living beings ; but this does not 

 affect the above definition. 



