CHAPTER III 

 THE PHYSICAL BASIS OF LIFE 



Over the structure of the chemical molecule rises the structure of 

 the living substance as a broader and higher kind of organization. 



— Hertwig. 



The realization that all animals and plants possess a funda- 

 mentally similar organization — the structural and physiological 

 units, or cells — leads quite naturally to an intensive study of the 

 material of which the cells are composed — the physical basis of 

 life itself. Accordingly we must now consider more specifically 

 the characteristics of this actual life-stuff — protoplasm. 



The old saying that the materials forming the human body 

 change completely every seven years is a tacit recognition that 

 lifeless material, in the form of food, is gradually transformed into 

 living matter under the active influence of the body. Indeed, just 

 as a geyser retains its individuality from moment to moment 

 though it is at no two instants composed of the same molecules of 

 water identically placed, so the living individual is a focus into 

 which materials enter, play a part for a time, and then emerge to 

 become dissipated in the environment. But here the analogy stops. 

 For in the living organism the materials which enter as food, en- 

 dowed with potential energy, are arranged and rearranged until 

 specific molecular combinations result, which in turn are trans- 

 formed into integral parts of the organization of life itself. How- 

 ever, to live is to work, and to work means expenditure — the 

 transformation of the potential into kinetic energy — with the 

 result that materials in relatively simple form and largely or en- 

 tirely devoid of energy are returned to the realm of the non-living. 

 And note, the living organism must continuously utilize energy 

 in order merely to maintain itself. Cessation is death. 



Thus we reach a fact of prime importance : so far as we know, 

 living matter — protoplasm — is merely ordinary matter that has 

 assumed, for the time being, unique physico-chemical relationships 

 that display the remarkable series of phenomena which we recog- 

 nize as LIFE. 



14 



