CHAPTER IV. 

 METHODS OF OBSERVING BACTERIA. 



WHOEVER would study bacteria must be equipped with 

 a good microscope. The instruments generally provided 

 for the use of medical students in college laboratories, as 

 well as those seldom-employed u show microscopes " seen 

 in physicians' offices, are ill adapted for the purpose. 

 The essential features of a bacteriological instrument 

 are lenses giving a clear magnification extending as 

 high as one thousand diameters, and a good condenser 

 for intensifying the lights thrown upon the objects. It 

 naturally follows that the best work requires the best 

 lenses. The cheapest good microscope which is at pres- 

 ent offered to the public is the BB. Continental stand, 

 made by Bausch and L,omb. This stand is provided with 

 everything necessary, is fitted with very creditable objec- 

 tives, including an excellent T y oil-immersion lens, and 

 seems capable of doing very good work. I do not 

 recommend this as the best instrument obtainable, but 

 as one that is both good and cheap. For those who desire 

 the very best the rather costly outfits made by Carl Zeiss 

 of Jena are unexcelled. 



For those who may begin the use of the Abbe con- 

 denser and oil-immersion lenses without the advantage 

 of personal instruction a few hints will not be out of 

 place : 



Always employ good slides without bubbles, and thin 

 cover-glasses ; No. i are best. 



Place a drop of oil of cedar upon the cover-glass of 

 the specimen to be examined ; rack the body of the instru- 

 ment down until the oil-immersion lens touches the oil ; 



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