54 WHAT IS LIFE 



The photosynthesis of carbohydrates in the Hving 

 plant obviously involves the problem of radiation — 

 one of the most difficult branches of physics. What 

 wave-lengths of light are the effective ones? What 

 does * 'absorption" of the rays mean? How, in what 

 way, does the atom or molecule react to radiation? 

 That sunlight exerts pressure has long been known 

 (Poynting^), but recent research — the Compton ef- 

 fect — would tend to show, recalling Newton's ideas, 

 that radiation is a discrete "corpuscular" quantity. 

 Consideration of all this and of the constitution of 

 the atoms (atomic physics,) then, necessarily enters 

 the problem of the formation of starches and sugars. 



About eighty -five per cent of the dry material of 

 the human body and a large percentage of the solids 

 of all living matter consists of proteins (proteids). 

 Proteins are classified as protamines, albumins, glob- 

 ulins, histones, glutelins, etc. They contain carbon 

 (about fifty to fifty -five per cent), hydrogen, nitrogen 

 (fifteen to over seventeen per cent), and oxygen. 

 Nearly all also contain a trace of sulphur, and a few 

 contain phosphorus, iron, etc. As a group, proteins 

 are well-characterized, and individual proteins are 

 very specific. However, they are highly complex 

 substances of unknown constitution, derived di- 

 rectly or indirectly from living matter. 



* The Pressure of Light. 



