2 GENERAL BIOLOGY 



unknown factors there may be, the greater becomes 

 our difficulty in reducing them to fundamental 

 principles. This is why biology is so strikingly an 

 "inexact" science in comparison with physics or 

 inorganic chemistry. Yet, it is not necessary even 

 for the physicist or the chemist to know what is the 

 ultimate nature of matter or force or electricity or 

 atoms in order to study such things and formulate 

 general laws based on such observation ; nor is it 

 necessary for the biologist to concern himself with 

 the meaning or nature of life in order to find out 

 what principles govern in the world of living things. 



The study and comparison of the structures of 

 plants and animals, of their methods of growth and 

 reproduction, their relation to each other and the 

 world about them, has revealed the fact that there 

 is an underlying unity in nature that makes it pos- 

 sible for us to sum up our observations in general 

 principles, incompletely understood, of course, but 

 more or less applicable to all living things. The 

 consideration of these general principles forms the 

 basis for a General Biology in the sense in which it 

 will be taken in the present work. 



Although we shall not attempt to elucidate life 

 in any philosophical sense, it is of interest, notwith- 

 standing, to discover at the start just how much 

 science can tell us of the nature of life, or of living 

 things as a whole. 



Living and Non-living. If a biologist should 

 ask the average layman whether he could tell the 



