CULTIVATION OF PARASITIC AMCEB^E. 67 



Bacillus coli or some other bacterium with which 

 amoebae grow well, and the feces is then smeared in 

 concentric circles upon the surface of the medium or in 

 streaks across it. The plates are then kept at room 

 temperature and examined upon successive days for 

 at least a week. The amoebae can be easily seen upon 

 the plates, as they wander from the material in the 

 spread out into the surrounding medium and the 

 course that they take can often be followed by the 

 development of colonies of the bacteria, which they 

 carry with them. 



Both Musgrave and Walker state that the de- 

 velopment of the parasitic species occurs more 

 readily at room temperature than in the incubator 

 at 37 C. As such species are normally subjected 

 to the temperature of the body, it is difficult to under- 

 stand why they should grow best under artificial con- 

 ditions at a lower temperature. This is certainly not 

 true of any other protozoon and suggests that all 

 their cultivated amoebae were really free-living forms. 

 In every instance where cultural forms of the protozoa 

 have been obtained, in which growth occurs at a lower 

 temperature than that of the host, such parasites 

 have depended for transmission upon some insect hav- 

 ing a low body temperature. There is no evidence 

 that the parasitic amoebae undergo ^ny development 

 in, or are transmitted by, an insect, and I consider that 



