ISOLATION OF BACTERIA IN PURE CULTURE 



543 



to their increased refractive power. As previously described, 

 a suitable scjuare of the agar is now excised and placed upon 

 the previously sterilized microscope sUde, which is most con- 

 \iently sterilized by flaming (cf. fig. 2). 



The microscope slide plus agar, which, for convenience sake, 

 I shall term "slide" in the following discussion, is placed on the 

 stage of the microscope, and an area is chosen where the organ- 

 isms are placed at a convenient mutual distance, commencing 



Fig. 1 



the examination where thej'' are Ijing close, and thence, by means 

 of the mechanical stage, proceeding to where they are lying 

 more scattered.' 



Having now come upon an area where there is one organism, 

 only, within the field of vision, and this single bacterium having 



1 The objective exployed by me was a Zeiss Apochromat; any suflSciently 

 powerful objective will however do. The magnification, at which I usually 

 worked, was 750 diameters. Illumination isa very important factor. The source 

 of light must be uniform. I used a powerful metal filament lamp with frosted 

 bulb, the light of which was considerably reduced by means of the diaphragm of 

 the illuminating apparatus of the microscope. 



