CHAPTER II 



PROTOPLASM: ITS MORPHOLOGY AND PHYSIOLOGY 



13. Life. — Life may be thought of in two somewhat distinct 

 ways. It may be considered, first, merely as an expression 

 for all the various activities of the organism, — the sum of 

 all the phenomena of its existence; or, second, as a force or 

 form of energy from which the special modes of activity, as 

 feeding, growth, motion, and thinking, arise. The latter is 

 the more common use of the term, and yet the former is the 

 only use of it which can be completely justified. Much of the 

 activity of living things may be explained by reference to 

 the ordinary physical and chemical laws. What we mean by 

 this is that all the so-called vital activities depend on such 

 physical facts as cohesion and adhesion, on the laws of fluids 

 and of solution of solids in fluids; and on such chemical facts 

 as the building up and tearing down of chemical compounds 

 composed of just the same elements that we find about us 

 everywhere in the world. There are a great many biologists 

 who think that there is nothing more in life than these physical 

 and chemical processes and effects, and that we should be able 

 to explain life and its activities if we knew all about the physics 

 and chemistry of living matter. It is sure, however, that there 

 are many vital phenomena which are not now to be explained 

 by what we now know of chemistry. Possibly this will always 

 be so. 



14. Living and Non-living Objects. — Any one of us could, 

 almost at a glance, tell whether an object is, or has been, alive; 

 and yet it is not easy to describe just what it is that convinces 

 us. There are two classes of differences between living things 

 and things that have never been associated with life : differences 

 (i) in make-up or organization, and (2) in powers. 



