NATURE OF LIFE x\ND LIVING MATERIAL 17 



realization of this hope appears possible in the immediate future. 

 Chemical analyses of many of the compounds found in protoplasm 

 have been made but they do not reveal why protoplasm is alive. 

 Nor are these analyses always wholly trustworthy as regards the 

 chemical structure of the substance in question when it is in the 

 living protoplasm, for sometimes the extraction of the substance for 

 chemical study alters it chemically. Our ideas concerning the chem- 

 ical processes of life are in part drawn from known facts and re- 

 liable analyses, and in part from inference from similarly reacting 

 non-living systems, for example, the behavior of gelatin as a chemi- 

 cal agent. 



Energy. If we consider for a moment the nature of the char- 

 acters that distinguish living bodies from non-living objects, we ar- 

 rive at the conclusion that all of them are indications of change, 

 of activity in the protoplasm of which the bodies are composed. 

 One of the first principles of mechanism is that wherever change 

 takes place, work is done. Power to do work is a property of proto- 

 plasm and power to do work is the usual definition of energy. 

 Energy is ordinarily measured by the amount of work it may per- 

 form. Energy, then, is involved in all the changes that are con- 

 stantly going on in the living organism. Energy occurs in a variety 

 of forms. It is convenient to think of it in terms of electrical energy, 

 chemical energy, radiant energy, heat, or mechanical energy, al- 

 though other forms are possible. Energy in action is spoken of as 

 KINETIC energy; the energy a body possesses by reason of its condi- 

 tion or position is known as potential energy. Kinetic energy may 

 become potential energy and potential energy may become kinetic. 

 When a weight is lifted, kinetic energy is expended in the effort, 

 but the weight now possesses an exactly equivalent amount of 

 potential energy by reason of its position. If energy is required in 

 forming a molecule of a compound, then that same amount of 

 energy resides in that molecule in potential form and becomes 

 kinetic, or, active when the molecule is broken down. If energy 



