THE STUDY OF ZOOLOGY 5 



strate functional features, a detailed knowledge of its anatomy 

 and physiology may be obtained; yet a far from satisfactory 

 conception of the animal as an organism is gained unless labora- 

 tory observations are supplemented by studying the animal 

 in its natural state in the field and thus noting its relationships to 

 other organisms and to its environment generally. Ecological 

 field studies often supply the key to morphological and functional 

 adaptations because adaptations are adjustments to environ- 

 mental conditions. Since different animals occupy different 

 stations or levels in the living world, a complex interlocking 

 environmental relationship has been built up, a knowledge of 

 which is necessary in order to gain a full understanding of any 

 given organism. But even after exhausting these avenues of 

 approach, the problem of the organism still presents difficulties 

 which can be removed — and not completely at that — only by 

 applying all the refinements of technique of the sciences of 

 physics and chemistry. The problem of the living thing is 

 beset with difficulties many and diverse because of the presence 

 in it of so many variable factors. 



The Protoplasm Doctrine. — From the point of view of the 

 biologist protoplasm is the living substance of which the bodies of 

 animals and plants are composed. The protoplasm doctrine 

 of life assumes that life is a development of protoplasm or that 

 life results from a certain physical and chemical combination of 

 matter such as occurs in protoplasm; that protoplasm is life. 

 This doctrine has not been proved — it is merely a working 

 hypothesis that has been more serviceable than any other 

 hypothesis in extending our knowledge of the nature of the 

 processes that go on in the living body. As a working 

 hypothesis it will be adhered to so long as its application yields 

 results. 



Physical Properties of Protoplasm. — All of the material of the 

 animal body is not living matter. Certain parts of the body such 

 as the hard covering of an insect or parts of the bone of the 

 vertebrate skeleton are products of the activity of the proto- 

 plasm; i.e., they are formed through the agency of living tissue 

 and serve definite functions but are not, strictly speaking, alive. 

 Such substances can scarcely be regarded as typical protoplasm. 

 Rather than call such substances dead material they may be 

 regarded as inert substances subject to the control of active 



