2 LIGHT AND LIFE 



purpose we can essentially disregard the atomic constitution of mat- 

 ter and confine ourselves to the account of the mechanical and elec- 

 trical properties of the materials used and to the application of the 

 simple laws governing the interaction between the parts of the ma- 

 chine. From biological research, however, it is evident that funda- 

 mental characteristics of living organisms, and in particular genetic 

 reproduction, depend primarily on processes on the atomic scale, 

 where we are faced with new problems. 



On the ground of classical physics, the very question of maintaining 

 a high degree of order of such immensely complicated systems pre- 

 sents serious difficulties. In fact, the incessant encounters between the 

 atoms with a more or less liqvud phase like the cytoplasm would 

 lead to rapidly increasing disorder. Doubts have even been expressed 

 about the compatibility of the existence and stability of living or- 

 ganisms with the laws of thermodynamics, but thorough investiga- 

 tion of the exchanges of energy and entropy accompanying the 

 metabolism and movements of the organisms has never disclosed 

 any departure from these laws. 



A whole new backgroimd has, however, been created by the de- 

 velopment of quantum physics, which, at the same time as it has 

 revealed an essential limitation of the deterministic description of 

 classical mechanics, has offered a proper basis for the account of the 

 stability of atomic and molecular structures. As is well known, no 

 picture on classical lines can be given of the electronic constitution 

 of atoms or of the behavior of the electrons responsible for the bind- 

 ings between atoms in chemical combinations. Owing to the large 

 masses of the atomic nuclei compared with that of the electron, it 

 is possible, however, effectively to retain a pictorial representation 

 of the relative positions of the atoms in accordance with the structure 

 formulae of chemistry, which have proved so adequate even lor the 

 highly complicated molecules with which we are concerned in organic 

 metabolism. 



In spite of the multifarious enzymatic processes involved in this 

 metabolism, the problem of the stability of the organisms presents a 

 fundamental simplicity, since, in the range of temperatures within 

 which life can be iq)held, the thermal fluctuations in the states of 

 vibration and rotation of the molecules are in general far from 

 sufficient to break the chemical bonds. Such fluctuations rather effect 

 the rapid disappearance of correlations between all secondary charac- 

 ters of the states of the reacting systems and permit us to account 

 for the primary features of their constitution merely by a specification 



