PART I. 



CHAPTER I. 



EXAMINATION OF BACTERIA WITH THE MICRO- 

 SCOPE, INCLUDING 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. It is a matter of convenience to have three 

 lenses attached to the body of the instrument by means of a triple 

 nose-piece, which permits any objective to be turned into the 

 optical axis at will. But a low power dry lens and an oil-im- 

 mersion objective are all that are essential for studying the 

 bacteria. 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 accomphsh the coarse adjustment, and 

 a more delicate 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 in- 

 serted. The iris diaphragm enables one to alter the size of the 

 opening as desired. Beneath the stage is a movable mirror, of 

 which one side is plane and the other concave. 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 

 variously designated by different makers, for instance, some 

 use letters, A, B, C, etc., others use numbers, i, 2, 3, etc., others 

 again give the focal distance, as f inch, \ inch, J inch, etc. 



