TECHNICAL APPENDIX. 167 



above, or, if we do not wish to soil the plate by open- 

 ing it, place it upon the cover and examine the colony 

 from below. This does not give such characteristic 

 appearances in all cases. 



B. High magnifying power. Oil immersion (seven 

 hundred to twelve hundred times) is used in the ob- 

 servation of individual bacteria. Upon the prepara- 

 tion is placed a drop of oil of cedar, the tube of the 

 microscope pushed down by means of the coarse ad- 

 justment until the lens just touches the surface of the 

 oil, and then adjust it accurately on the preparation 

 with the micrometer screw. 



(a) Unstained Preparations. Narrow diaphragm. 

 They are examined in two ways : 



1. A drop of a fluid pure culture or a drop of water 

 mixed with a trace of pure culture is placed between 

 the slide and cover-glass ; or 



2. In the hanging drop. A platinum loopful of 

 fluid pure culture, or a loopful of bouillon mixed with 

 a trace of pure culture, is placed 



on a cover-glass, and this laid 



(reversed) upon a slide which 



has been hollowed out so that the drop lies in the 



cavity. The cover-glass is then fixed to the slide 



by applying a trace of water to the four corners of 



the cover-glass or by applying vaseline, if prolonged 



observation is required. 



(b) Stained Preparations. Open diaphragm. 

 Abbe's illuminating apparatus. To observe double- 

 stained section preparations we require wide dia- 

 phragm for the bacteria and narrow diaphragm for 

 the tissues. 



C. Cleansing of the preparations and the micro- 



