BIOLOGY 



CHAPTER I 



THE SCOPE OF BIOLOGY 

 THE NEW BIOLOGY AND THE OLD 



BIOLOGY is often described as the most recent of the sciences, 

 despite the fact that it was one of the first to be studied. Four 

 centuries before Christ, animals were dissected and described 

 by Aristotle, and from that time on, the study of living things 

 has never ceased. In the last half century, however, the study 

 of vital phenomena has assumed a new aspect. Formerly 

 animals and plants were studied only as objects to be classified 

 and named; now they are studied as objects to be explained. 



Progress of Scientific Thought. This new method of bi- 

 ological study is only another expression of man's changed 

 attitude toward all natural phenomena. In early times, people 

 imagined that all the phenomena of nature which they could 

 not understand were produced by gods. One god caused the 

 winds; another the motions of the sun and stars. Gradually 

 these conceptions have been changed by the attitude of modern 

 science. First, the motions of the heavenly bodies were ex- 

 plained under the general law of gravitation. Then, the mys- 

 terious phenomena of fire and of electricity were comprehended 

 under the laws of chemistry and physics. Later, the various 

 changes on the earth's surface, such as the formation of moun- 

 tains, of valleys, of rivers, and of plains, were explained as the 

 result of the ordinary forces of nature. 



In all this there has been a progress in one direction, namely, 

 toward the explanation of natural phenomena by natural 

 forces. The most recent of the natural phenomena to be 

 studied with this end in view, are those associated with living 



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