PART I. 



CHAPTER I. 



EXAMINATION OF BACTERIA WITH THE MICROSCOPE, IN- 

 CLUDING METHODS OF STAINING. 



The Microscope. The microscope consists of a tubular 

 body which carries the optical parts, and which can be 

 raised or lowered for focusing. The objectives should be 

 three in number, and should be attached to the body by 

 means of a triple nose-piece, which permits any objective 

 to be turned into the optical axis at will. The eye-piece 

 slips into the upper and opposite end of the body or tube. 

 The arrangements for focusing consist of a rack and pinion 

 which accomplish the coarse adjustment, and a more deli- 

 cate fine adjustment. The stage, upon which the objects 

 to be examined are placed, has an opening in the middle. 

 In this opening an iris diaphragm and Abbe condenser are 

 inserted. The iris diaphragm enables one to alter the size 

 of the opening as desired. Beneath the stage is a mov- 

 able mirror, of which one side is plane and the other con- 

 cave. All of these parts are supported on a short, heavy 

 pillar which is fixed in the horseshoe-shaped base. 



The essential parts of the microscope are, of course, the 

 eye-piece (German, Ocular), and the objective. Objectives 

 are given various names by different makers, for instance, 

 A, B, C, etc., or i, 2, 3, etc.; or they are named according 

 to their focal distances, as f inch, J inch, -J inch, etc. In 

 bacteriological work a rather " low power " or J inch 



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