232 ORIGIN OF STRUCTURES AND FUNCTIONS 



Doffin, 1953"). Others regarded protoplasm as no more than 

 a specific medium, a mixture of lifeless compounds contain- 

 ing the hypothetical living particles, the protein molecules, 

 in the chemical structure of which there lie concealed all the 

 causes and mysteries of life. We may refer here to the 

 ' biogens ' of M. Verworn,^^ the ' moleculobionts ' of Alex- 

 ander and Bridges^'' and other similar hypothetical particles, 

 the chemical reality of which has never been proved by 

 anyone, though references to them are still to be met with in 

 scientific literature. 



Thus contemporary chemists and biologists use the word 

 ' protein ' in a long series of different senses. At one end 

 of the series we have the purely chemical definition of 

 proteins as highly polymerised organic compounds with very 

 complicated molecules made up of different sorts of amino 

 acids. This definition would, however, seem to be very one- 

 sided. It ignores the biologically important properties pos- 

 sessed by all the various proteins which have actually been 

 isolated from organisms, properties which are related to the 

 individual peculiarities of their structure. Such a definition 

 would include all polymers of amino acids, even such possible 

 combinations of amino acids as would not subserve the 

 biological functions proper to naturally occurring proteins. 

 Polymers of amino acids of this sort would naturally be 

 unable to form part of the structure of living matter. This 

 purely chemical definition, therefore, includes among proteins 

 even substances which have no direct biological significance. 

 On the other hand, the definition which we find at the other 

 end of our series, that of the living protein molecule, is 

 completely lacking in any clear-cut chemical meaning. The 

 partisans of this concept attribute to the protein molecule 

 (in most cases they refer to molecules of nucleoproteins) all 

 the properties of life, i.e. the ability to metabolise, reproduce 

 themselves, etc. However, they give absolutely no real 

 explanation of how all these properties could depend on any 

 particular arrangement of the atoms in the hypothetical 

 ' living molecule '. 



As a result of this confusion, many contemporary authors 

 studying the origin of life make quite arbitrary and illogical 

 jumps between the concepts of protein implied by the purely 



