CHAPTER II 



MICROSCOPICAL TECHNIQUE 



The student of bacteriology should be familiar with the 

 use of the compound microscope. If experience with this 

 instrument has been gained in other fields of biology, the 

 peculiar methods of bacteriology are easily acquired. If, how- 

 ever, the student has had no previous training, he should 

 familiarize himself with the construction and purposes of the 

 different parts of the microscope by a perusal of the book- 

 lets issued by various optical companies on the use and care 

 of the microscope, and by a study of the first three chapters 

 in Winslow's Elements of Applied Microscopy. 



The microscope and its accessories. The microscope for 

 bacteriological purposes should be provided with both a coarse 

 and a fine adjustment, with three objectives, 16 mm.(| inch), 

 4 mm. (\ inch), and 2 mm. (^ inch), equivalent focus, two 

 oculars, 25 mm. (1 inch) and 50 mm. (2 inch), a triple nose 

 piece, so that the objectives can be easily changed, and an Abbe 

 substage condenser, with iris diaphragms both above and be- 

 low the lens of the condenser. The Abbe condenser and the 

 yV-inch oil-immersion lens are indispensable to the ordinary 

 equipment of a compound microscope for bacteriological work. 



In the examination of bacteria high powers of magnifica- 

 tion must be used (500-800 diameters). In order to secure 

 these magnifications very small lenses must be employed, 

 thus restricting the amount of light passing through them. 

 The modifications of the ordinary compound microscope, to 



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