PART II 

 LIFE PROCESSES OF THE ORGANISM 



CHAPTER IV 

 LIVING THINGS AND NON-LIVING THINGS 



23. Living bodies formed. A comparison of living and non- 

 living objects brings to our attention the fact that, whereas the 

 non-living objects of nature are, as a rule, indefinitely shaped 

 masses of matter, the plants and animals with which we are 

 acquainted generally have rather definite shapes, or forms. It 

 is true that crystals of various substances have definite, char- 

 acteristic forms, and it is true also that no two trees or no 

 two animals have exactly the same form. Nevertheless we 

 have no difficulty in distinguishing different kinds of plants 

 or animals by their forms, whereas, besides crystals, we do not 

 find many non-living (natural) objects that show distinct forms. 



24. Living bodies organized. Living bodies are like machines 

 in being made up of several fairly distinct parts. Each of these 

 parts acts not usually by itself, but with the cooperation of 

 others and toward some result that concerns the body as a 

 whole. Each part of a living body that carries on some distinct 

 share of the total work is called an organ. The arms and legs 

 and wings of animals are organs of locomotion. The eyes and 

 feelers and ears are organs of sensation. The stomach and liver 

 are organs of digestion. The body of a plant or an animal is 

 often spoken of as an organisin — something made up of organs. 



Functions. The special work performed by an organ is called its 

 function ; and the study of functions constitutes a large part of 

 biology, called physiology. Thus, we may say that the function of 



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