Ill 



THE PREPARATION OF " PURE MIXED 

 CULTURES" OF AMCEBA 



Definition. By the term " pure mixed culture " 

 of amoeba is meant the cultivation together of a 

 single species of amoeba with a pure strain of a 

 bacterium. This must be carefully distinguished 

 from the expression " pure culture," which involves 

 the cultivation of the amoeba without any living 

 bacteria at all. 



Introduction. In the course of our previous 

 experiments we had always been faced with the 

 difficulty that an organism requires food for its 

 existence to be maintained, and that when testing 

 the action of auxetics and kinetics in exciting 

 reproduction through more than one generation 

 the possible influence of substances produced by the 

 breaking down of the food, which are themselves 

 auxetics and kinetics, has had to be borne in mind. 

 By reducing the nature of the food to a uniform 

 condition we hoped to be able to compare the 

 rate of growth in cases where auxetics and kinetics 

 were deliberately added with those in which these 

 substances were absent. The object, then, of the 

 preparation of " pure mixed cultures " was to 

 .eliminate from the environment of the amoebae the 



