364 THE FIRST ORGANISMS 



results obtained from them are still very modest. Therefore, 

 if we wish to formulate any sort of idea concerning the actual 

 forms which developed during the course of evolution from 

 the original systems to the first organisms, we must make as 

 much use as possible of the data of comparative biochemistry 

 (this is done more fully in the next chapter) and the results 

 obtained from a study of the metabolism, or separate aspects 

 of the metabolism, of isolated protoplasmic structures and 

 collections of enzymic systems. In this way we may be able 

 to reveal various features common to all living organisms 

 and may try to form a mental picture of how these features 

 could have arisen during the process of directed evolution 

 of our original systems or in the earliest stages of the develop- 

 ment of life. 



As we have remarked again and again, the fundamental 

 organisation of living matter is its organisation in tim.e. The 

 phenomena which take place in it in a definite, regular order 

 together constitute its metabolism. 



The individual reactions which occur in protoplasm are 

 rather simple and uniform. They are the reactions, familiar 

 to chemists, of oxidation, reduction, hydrolysis, phosphoro- 

 lysis, aldol condensation, the breaking of carbon-carbon 

 bonds, etc. Any of these may be brought about outside the 

 organism and there is nothing specifically vital about them. 

 What would seem to be specific to living bodies is the definite 

 organisation in time of these reactions in them, to form a 

 single complete system, an abundantly branching network 

 of reactions. In living bodies these reactions do not take 

 place chaotically but bear a strictly determined relationship 

 to one another. The colossal diversity of organic compounds 

 which is to be found in the world of living things does not 

 depend on diversity and complication of the separate indi- 

 vidual reactions but on the diversity of their combinations, 

 the variations in the order in which they occur in the 

 different cells of the organism at particular stages of develop- 

 ment. This sequence of chemical reactions forms the basis 

 of both the synthesis and the breakdown of the substances 

 of protoplasm. It forms the basis of such vital phenomena as 

 the synthesis of proteins, fermentation, respiration, photo- 

 synthesis, etc. In the respiratory and photosynthetic processes 



