140 WARFARE IN THE HUMAN BODY 



to deal with the assaults it undergoes ; in some cases 

 changing and making use of what it ingests, in others 

 altering bodies which cannot be used, but may be made 

 harmless. 



The points of the likeness between a catalyst and 

 an engine or tool are many. It is something made, a 

 reaction to needs. It works and remains the same. It 

 only wears out gradually. It makes a long process short, 

 a difficult one easy. It can build up and break down. 

 Such qualities can be seen in a sociological example if 

 we take two living communities, or societies combining 

 for a common purpose, for then combinations will result 

 which have the most remarkable likeness to such catalysts, 

 and exhibit biological phenomena which throw a light 

 on the reason that enzyme bodies have reversible re- 

 actions. We may, for instance, suppose that a botanical 

 and a zoological society find it necessary for purposes of 

 existence to take a common house. It is obvious that 

 we have here a symbiotic but not necessarily a symphilic 

 community, and it is equally obvious that both original 

 purposes must be served, or the whole structure fails. To 

 carry on work some of the individuals must represent the 

 others, and this common secretarial office remains as a 

 formed reaction body or engine for getting the work done. 

 When one society is most active at any given time its 

 action may be regarded as synthetic so far as it is con- 

 cerned, and the process implies a temporary displacement 

 or breaking down of the others. When this is over the 

 reverse action takes place. But all the time the formed 

 reaction or joint secretarial body remains. An enzyme 

 can thus be compared with the common alternative 

 executive of at least a double body which has different 

 internal but common external ends. However extravagant 



