Laboratory Outline for General Bacteriology 



All apparent measurements have to be corrected by multiplying 

 by a microscope constant. This varies for the different microscopes. 



12. Clean the oil immersion objective with lens paper imme- 

 diately after using. 



13. With the Bausch & Lomb microscope using the 10X eye- 

 piece and the 1/6 objective the magnification is 430 and the working 

 distance is .3 mm. With the 1/12 objective the magnification is 950 

 and the working distance is .15 mm. 



MEASUREMENT OF BACTERIA 



For measuring bacteria use the highest power objective the 

 1/12 oil immersion. When an object is magnified 1000 times light 

 is diminished at the same rate and the Abbe condenser is necessary 

 in order to increase the light sufficiently to see the object. 



Raise the condenser as high as possible. It is regulated by 

 a screw at the left side under the stage. 



Place a drop of cedar oil on the preparation to be examined. 

 The oil has the same refractive index as the glass and prevents 

 dispersion of the rays of light. 



Lower the objective into the oil while looking at it from the 

 side. 



Adjust the mirror to give the desired amount of light. Usually 

 the full amount is best unless the light is exceptionally bright. Use 

 the plane mirror for daylight and the concave for artificial light. 



With the eye at the microscope focus up slowly with the fine 

 adjustment until the object shows clearly. 



In the eyepiece is a ruled scale by which bacteria are measured. 

 The eyepiece is ruled to 1/10 millimeter. The space between num- 

 bers on the scale is one millimeter. A micron is 1/1000 of a milli- 

 meter or 1/1,000,000 of a meter, which magnified by the microscope 

 covers about .7 of the space between two lines on the eyepiece 

 micrometer. The magnification of different microscopes varies 

 slightly so all have been tested with a stage micrometer and the 

 factor or microscope constant determined. This microscope con- 

 stant is marked on the stage of the microscope. All apparent 

 measurements have to be multiplied by this factor to get the actual 

 measurements. 



The following four stained preparations are furnished : 

 No. 19 B. mesentericus 

 32 Micrococcus agilis 

 114 Bact. aerogenes 

 84 Sarcina flava 



Note the shape and arrangement of the bacteria and measure 

 their size. Bacteria of the same kind vary somewhat in size so 



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