THE PHYSICAL BASIS OF LIFE 15 



But non-living matter is always closely associated with living 

 matter in the bodies of animals and plants. Indeed, the two are 

 so intimately related that it is frequently difficult to distinguish 

 sharply between them. Obviously, in the human body, for in- 

 stance, the visible parts of hair and nails, a large part of bone, and 

 the liquid part of blood are non-living material. But the non-living 

 is not confined to gross structures, for the dead among the living 

 is still revealed until the penetrating power of the microscope 

 fails us. 



A. The Protoplasm Concept 



Although there is a continuous stream of matter and energy 

 flowing through the living individual, nevertheless the physical 

 and chemical study of living matter from whatever source we take 

 it — Mold or Elm, Amoeba or Man — reveals a striking similarity 

 in its fundamental factors, and this is the basis of the protoplasm 

 concept held by modern biologists. 



As the finer structure of animals and plants came within the 

 range of vision through improvements in microscope lenses, it was 

 gradually recognized that the ultimate living part appeared to be 

 a granular, viscid fluid. This started a long series of studies on the 

 materials of the bodies of unicellular organisms similar to Amoeba 

 and of the cellular elements of higher animals and plants, which 

 finally led, about the middle of the last century, to the complete 

 demonstration of the full morphological and physiological signifi- 

 cance of protoplasm. There is, in truth, an essentially similar, 

 fundamental, living material of both animals and plants — a com- 

 mon physical basis of life. This reduction of all life phenomena to 

 a common denominator laid the foundations for — indeed, actu- 

 ally established — the life-science, biology. (Figs. 6, 9.) 



Although we speak of a common 'physical basis of life,' it is of 

 paramount importance to bear in mind that the protoplasm of no 

 two animals or plants or, indeed, of different parts of the same 

 animal or plant is exactly the same. Identity of protoplasm would 

 mean identity of structure and function — identity of life itself. 

 The concept protoplasm merely emphasizes that, after allowances 

 are made for all the variations, we still have the similarities far 

 outnumbering the dissimilarities in the ' agent of vital manifesta- 

 tions.' 



The physical chemists tell us that protoplasm consists of matter 



