362 THE FIRST ORGANISMS 



at a given stage in their life cycles, chemical transformations 

 are carried out within them in a definite, co-ordinated 

 sequence. The constancy of the formation of the substances 

 is simply a manifestation of the constancy of the sequences 

 of the reactions. Here there is no * self-reproduction ' of 

 molecules in the literal sense of the term, no multiplication 

 of them ; here new molecules of exactly the same kind are 

 repeatedly produced. The sequence of reactions on which 

 this phenomenon is based does not depend on any single 

 individual factor but is a manifestation of the whole organisa- 

 tion of the protoplasm in its relationship to its environment. 

 As we saw in Chapter VI, the biosynthesis of proteins 

 constitutes no exception in this respect. Attempts to treat it 

 as an autocatalytic process, in which one molecule of a given 

 substance arises as a result of the catalytic activity of another 

 of exactly the same sort which was already present, have 

 recently proved a complete fiasco. The experiments of A. 

 Gierer and G. Schramm^^ are particularly convincing in this 

 connection. They showed that a single nucleic acid of tobacco 

 mosaic virus completely freed from protein, when introduced 

 into the plant, will evoke the formation in it of a specific 

 protein which was not previously present in the plant. In 

 this case there could be no question of any autocatalysis in 

 the strictly chemical sense of the term. There was only 

 definite co-ordinated interaction of all the processes of the 

 cells of the tobacco leaf, which were somewhat altered in 

 character by the introduction of a new factor, the viral nucleic 

 acid. The nucleic acid as an individual substance, a com- 

 pound considered in isolation, could certainly not synthesise 

 a protein by itself. It is only effective against the general 

 background of the whole metabolism of the tobacco plant, 

 as is confirmed by all the evidence at present available. The 

 harmonious participation of a long series of catalytic systems 

 is required for the biosynthesis of proteins, some providing 

 the energy needed for the synthesis, some determining the 

 strictly regular and constant relationship between the rates 

 of the different reactions and, finally, some systems which 

 control the spatial organisation of the protein molecule in 

 the process of its synthesis. Among these systems which deter- 

 mine the specific structure of the protein, nucleic acid plays 



