CHAPTEK VI 



THE PHYSICO-CHEMICAL BASIS OF IMMUNITY AND OF EVOLUTION 



If we endeavour now to gather together the conclusions which 

 may reasonably be reached from a consideration of the data 

 afforded in the previous chapters, they appear to be the following : 



(i.) Instead of there being no such thing as direct adaptation 

 or equilibration of the individual to his surroundings in the 

 Spencerian sense, this surely exists and can be demonstrated. 



(ii.) In the lowest forms of life, among the bacteria, it can 

 be demonstrated that not only is this adaptation individual, 

 but that acquired properties of certain orders are inherited 

 through numerous generations, even when the cause which set 

 up the original modification has ceased to act. 



(iii.) It can further be demonstrated that the inheritance 

 is not due to the survival and perpetuation of those individuals 

 only which present the favourable variation. All the members 

 of a given strain of bacteria subjected to a given modification 

 of environment can be made to vary in the same direction, and 

 acquire and transmit the same new property. 



(iv.) Immunization of the higher animals is direct adapta- 

 tion. There could, in fact, be no clearer demonstration of the 

 process of direct adaptation than has been afforded by the 

 abundant researches upon the production of immunity. 



(v.) It is clearly proved that there are drugs and toxines 

 which, acting on the tissues of the body, act also on the germ 

 cells, causing modification of the latter, of such a nature that 

 the offspring resulting from these germ cells are modified. 



(vi.) The clearest evidences of this action are in connexion 

 with drugs and toxines which lead to conditions of defect, but 

 acquired special susceptibility and anaphylactic reaction are 



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