photosynthesis, in which the solar energy enters into the living 

 world to drive it. In this reaction the radiation is captured by dyes, 

 mostly chlorophyll, in which it produces an electronic excitation. 

 This E* is then stabilized in the form of (£). Subsequently (£) 

 is shifted from one bond or molecule to another until, eventually, 

 it is stored away in the form of the (£) of carbohydrates or fats. 

 The process of photosynthesis could thus be symbolized by: 



hv-^E*-^ (£0 -> (£2) -> (£3) ^ (£n) 



The reverse process occurs in photoluminescence when, for in- 

 stance, the firefly emits light: 



(£„) -^ (£3) -> (£2) -> (£1) -^E* -^hv 



Looking at this row of reactions one cannot fail to notice its 

 identity with that of photosynthesis. Only the order is reversed. If 

 we look upon the production of light by the firefly only as upon an 

 example of production of work, w, then we arrive at the conclu- 

 sion that the energetics of the living world consist of only two 

 processes: photosynthesis and its reversal. 



In muscle £1, which is directly fed into the contractile mecha- 

 nism, is the (£) of ATP, and the recent work of Arnon and his 

 associates indicates that ATP plays a very intimate role in the first 

 steps of photosynthesis, while Strehler and Arnold, and Arnold 

 and Davidson have shown photosynthesis to be reversible. 



In the above reactions (£«) -> (£1) is what is called "inter- 

 mediary metabolism." The problem to be dealt with in this book 

 is whether (£1) -» £* -^ w does not represent the reaction which 

 drives the living machine and, belonging in the realm of quantum 

 mechanics, can be expressed only in terms of the latter. 



Such a question cannot be answered by any single experiment. 

 Only the accumulation of data on various lines can make such a 

 theory acceptable. If correct, this theory should lead us to a better 

 understanding of various biological structures and phenomena, 

 should open new views and suggest new experiments. 



