THE THEORY OF IMMUNITY 141 



such a homely illustration may appear it probably repre- 

 sents actual biochemical facts ; for it shows how two 

 molecules living in hostile symbiosis must affect each 

 other and produce reaction bodies which are highly complex, 

 and represent in turn the energies of each molecule. Such 

 a view affords a reasonable ground of explanation for the 

 reversible reactions of catalysts themselves. Without such 

 reactions it is not easy to follow the possible ways of growth. 



It will not seem absurd to some if it is said that these 

 likenesses are to be found at the bottom of all growth, 

 whether of atoms or nations, and that they are part of a 

 universal law which may be expressed thus : All life and 

 growth is fundamentally the forced result of a symbiosis 

 of differing bodies in which hostile energies become the 

 common, mutual, and reciprocal internal stimuli of the 

 conjoint individual. This includes all living things from 

 the two molecules (or more), each with a catalyst, which 

 probably make up the simplest form of life. 



To summarize the views expressed it may be said that— 

 (i) To understand immunity it must include all processes 

 of nutrition. (2) All unsplit ingested bodies are " poison- 

 ous " or rejected as neutral and useless. (3) Enzymes 

 are the catalysts which build up for storage or break 

 down for use. (4) Immune bodies in infections are pro- 

 voked catalysts dealing more or less well with the sub- 

 strate bacterium, or toxin. (5) Poisons, metallic or 

 alkaloid, etc., when tolerance is established, have pro- 

 voked a catalyst to deal with them. (6) " Complement ' 

 is not a fixed quantity, but the special or general com- 

 bining body used by the catalyst and the substrate. 

 (7) Many of the difficulties experienced by bacteriologists 

 in reaching satisfactory conclusions on immunity are due 

 to their neglect of colloidal chemistry. 



