CULTIVATION OF PARASITIC AMOEBAE. 69 



away from the streak of bacterial growth; the plate 

 is then turned right side up, the cover removed, and 

 with carbolated vaseline the V-shape mark is traced 

 on the surface of the medium. In this manner the 

 single amoeba is isolated and can be transferred, after 

 multiplication, to a new plate. It is well to cover the 

 surface of the medium outside the arms of the V with 

 a little additional vaseline. 



The Cover-glass Method of Cultivation. This 

 very ingenious method of cultivating amoebse was de- 

 vised by Walker and is thus described by him: 



" It is based on the principle of Koch's original 

 plate culture for bacteria, is indeed a miniature Koch's 

 plate culture made on a cover-glass and inverted over 

 a concave slide. For this reason I have called such 

 culture a * hanging plate culture.' This culture is 

 prepared as follows: A thin seven-eighths-inch cover 

 glass is flamed and placed under a flamed watch glass. 

 With a sterile loop a large loopful of the liquefied 

 agar medium is transferred to the sterile cover, and 

 spread in a uniform, thin and circumscribed layer. 

 This film of agar will solidify almost instantly and 

 it is at once inoculated with the amoeba culture. The 

 cover-glass culture is then inverted over the concave 

 centre of a hollow slide, which has been previously 

 flamed, ringed with vaseline, and kept in an inverted 

 position near at hand. This transfer of the cover- 



