CHAPTER II 



THE ANIMAL ORGANISM AND ITS ENVIRONMENTAL RELATIONS 



I. Nature of Living Substance 



The bodies of living plants and animals are made up of living matter 

 known as protoplasm (35, chap. ii). Protoplasm is a chemical substance 

 or a mixture of chemical substances. It is very difficult to distinguish 

 living and non-living matter by definition. However, we experience 

 little difficulty in separating living from non-living things. This is 

 because living things usually possess certain definite forms and ability to 

 reproduce and move (especially animals). They also possess irritability. 

 This is the property by virtue of which the force applied to living sub- 

 stance is not in proportion to the force resulting (35, p. 124). One 

 strikes a horse with a whip ; the energy which the horse exerts in running 

 is not proportional to the force of the blow, but is far greater. 



In considering the environmental relations of animals, we shall 

 separate our discussion into that concerned with form and that con- 

 cerned with movement (motor activity) and other functional manifesta- 

 tions. The term function is understood to cover all action on the part 

 of the various parts of the organisms, motor activity included (35a, 

 chaps, vii, viii, and ix). 



II. The Relation of Form or Structure to Function 



The term animal calls forth a mental picture of activity and 

 movement. The animals with which we are most familiar are those of 

 large size, such as fishes, birds, and mammals. They and the groups 

 to which they belong represent only a very small part of the animal 

 kingdom, but we may consider one of these familiar animals as an 

 example of animals in general. The black bass will serve our purpose. 



Such a fish is a complicated, highly organized animal (36, p. 183), 

 possessing many organs, such as fins, gills, teeth, a stomach, an intestine, 

 a liver, a heart, and a brain and spinal cord harnessed to the rest of the 

 body by a series of small nerves which control all the organs. The fins, 

 which are the external organs of locomotion, are sufficient in number to 

 control the body and force it forward. The muscles which move the 

 fins must receive nourishment in order to do their work. The nourish- 

 ment is carried in blood-vessels, and the fluid which bears the nourish- 



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