CHAPTER II 



CELLS AND THE CELL THEORY 



ORGANISMS 



ONE characteristic feature of living matter is that it is not 

 indefinitely distributed around the world, but is always asso- 

 ciated in distinct units or individuals. In other words, there 

 is no life apart from individuals. These units always contain 

 different parts, each with a distinct function. This is very 

 evident among well-known animals and plants. The human 

 body possesses a heart, a stomach, a brain; and a tree has 

 roots, leaves, flowers, etc. These different parts are called 

 organs ; and because it possesses organs, a living being is called 

 an organism. While it is true that practically all living things 

 do have organs, some of the lowest are so small that no organs 

 have yet been found in them, as for example, bacteria; see 

 Fig. 7. It is probable, however, that these do have organs 

 if we were only able to see them; at all events, the term organ- 

 ism is extended to all living things whether they possess evi- 

 dent organs or not. 



From the word organisms is coined the adjective organic, that 

 is, pertaining to organisms. Organic substances have been pro- 

 duced by living beings, while inorganic substances have no con- 

 nection with living things. Bone, muscle, wood, sugar, coal, etc., 

 are organic; while stones, water, and air are inorganic. Nearly 

 all organic substances contain carbon and are capable of being 

 burned, while inorganic substances usually contain no carbon. 



THE CELL AS THE UNIT OF ORGANIC STRUCTURE 



The slightest familiarity with the larger well-known animals 

 and plants shows not only that they are made up of different 

 organs, each with its definite duty to perform, but also that these 

 organs are composed of different parts, each having its specific 



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