Introduction 



inY, REALM OF LIVING THINGS BEING A PART OF NATURE 



is contiguous to the non-living world. Living things have 

 material composition, are made up finally of units, mole- 

 cules, atoms, and electrons, as surely as any non-living 

 matter. Like all forms in nature they have chemical struc- 

 ture and physical properties, are physico-chemical systems. 

 As such they obey the laws of physics and chemistry. 

 Would one deny this fact, one would thereby deny the 

 possibility of any scientific investigation of living things. 

 No matter what beliefs we entertain, the noblest and purest, 

 concerning life as something apart from physical and chemi- 

 cal phenomena, we can not with the mental equipment 

 which we now possess reach any estimate of living things as 

 apart from the remainder of the physico-chemical world. 



But although any living thing, being matter, is a physico- 

 chemical system, it differs from matter which constitutes 

 the non-living. This difference exists and would continue 

 to exist were some chemist at this moment to succeed to 

 synthesize out of non-living matter a living thing. The 

 analysis of living things reveals that they are composed of 

 no peculiar chemical elements — instead, they are made up 

 of those most commonly occurring. The difference can not 

 then be attributed to the elements. To be sure, certain 

 complex compounds, as proteins, carbohydrates and lipins 

 (fats and fat-like substances) — themselves compounded 

 mainly of the commonly occurring elements, carbon, hydro- 

 gen and oxygen, and never of rare elements — are peculiar 



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