CULTIVATION OF PARASITIC AMOEBJC. 65 



Agar 20.0 grams. 



Sodium chloride 0.3-0.5 gram. 



Extract of beef 0.3-0.5 gram. 



Distilled water 1000. c.c. 



This is prepared exactly as is ordinary nutrient 

 agar and is made 1 per cent, alkaline, using phenol- 

 phthalein as an indicator. Upon this medium numer- 

 ous species of free-living amoebse develop, provided 

 suitable bacteria are present in symbiosis. Musgrave 

 and Clegg have determined that many amoebae are 

 very selective in regard to the bacteria with which they 

 will develop, and they regard failures to grow amoebse 

 as largely due to the absence of a suitable symbiotic 

 bacterium. 



Because of this selective action of the amoebae it 

 is possible to grow them in pure culture with a single 

 species of bacterium and these cultures are known as 

 :< pure mixed cultures of amoebae." Of the bacteria 

 which have been found most suitable for cultivation 

 with amoebae may be mentioned Bacillus coti, Vibrio 

 cholerce, Bacillus typliosus, Staphylococcus pyogenes 

 aureus and such non-pathogenic organisms as Bacillus 

 fluorescens and Bacillus rubra. 



It is a significant fact that in most of the experi- 

 ments resulting in the production of pathogenic lesions 

 by the use of cultures of amoebae, the bacteria grown in 

 symbiosis with the amoebae have been pathogenic 

 species. For this reason the results must be regarded 



