EVOLUTION 21 



predict whether such compounds will ever be synthesized 

 in our laboratories, but the analogy which has been made 

 use of throughout this discussion may be of use here. 

 It may even be permissible to go further and to suggest 

 that the analogy which it has been attempted to establish 

 between an organism and a chemical molecule, in the 

 initicd stages of ' vitality ' passes from an analogy into 

 a physical reality. The nearest approach to responsivity 

 which modem chemistry can offer is among those com- 

 poimds which have been referred to as tautomeric, 

 using this term in a general sense so as to cover all cases 

 of mobile configuration. This is the kind of instability 

 among stable compounds which most nearly complies 

 with the biological conditions. But such cases are at 

 present limited both in number and in phase. In spite 

 of the great complexity of many synthetical compounds 

 the number of definite forms capable of being assumed 

 in cases of tautomerism is generally limited to two, or, it 

 may be said that the possibilities of assuming atomic 

 configurations in response to chemical and physiced 

 stimuli are in these cases limited to two. 



Now there is physical and, especially, optical evidence 

 in support of the view that certain molecules in which 

 the atoms are capable of assuming two or more different 

 configurations may, under different external conditions, 

 exist in varying proportions in two or more forms simul- 

 taneously. In such cases two or more atomic configurations 

 may be said to be adapted to a particular environment. 



molecular mobility'of atomic configuration and not in the purely physical 

 sense in which Spencer uses the term when discussing the chemical 

 composition of organic and organized matter in Chapter I of the 

 Principles of Biology. Growth in the initial stages of the development 

 of living from lifeless organic matter would from this point of view 

 be more analogous to inorganic growth, just in the same way that the 

 primordial ' organized ' carbon compounds were more closely related 

 to dead carbon compounds. If it is claimed that the special and 

 distinguishing character of Uving matter is its power of ' directing ' 

 without creating energy, may not the action of catalysts or ' contact ' 

 substances, which direct the course of chemical change without under- 

 going any change themselves be put forward as an analogue ? 



