CHAPTER III 

 METHODS OF STUDYING BACTERIA 



While bacteria can be seen with high-power magnify- 

 ing glasses, it is impossible to study their form without 

 a compound microscope. Such an instrument is shown 

 in Fig. 7. 



It consists of a heavy foot or base bearing an upright 

 post, to which the stage and the tube are attached. 

 The object to be examined is placed on the stage, and 

 light is thrown up from the mirror beneath, through the 

 object, and into the series of lenses in the tube. The 

 tube is moved up and down by means of two screws, one 

 called the coarse adjustment, the other called the fine 

 adjustment. Fitting into the upper end of the tube are 

 various eye-pieces or oculars. These are of varying 

 power and are usually numbered from 1 to 5. Attached 

 to the lower end of the tube is a so-called nose-piece, 

 carrying two or three ' 'objectives," each objective con- 

 sisting of a series of lenses mounted together. The 

 objectives are usually distinguished by numbers (3, 5, 

 and 7) or by fractions (§, J, and J inch). When 

 using the higher powers of the microscope it is important 

 to have strong illumination from the mirror. In order 

 to bring this about a series of lenses, called the con- 

 denser, is placed between the mirror and the stage. 

 But even with this equipment it is difficult to study 

 the finer details of bacterial structure. This can only 



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