METHODS OF EXAMINATION. 27 



shutting off part of the light a Blender. When the bacteria 

 have been found, and their relation to the structure is then 

 wished to be studied, the " Abbe" is generally shut out by the 

 Iris blender, and the structure comes more plainly into view. 



FIG. 8. 



Iris Blender. 



For all stained Bacteria the oil immersion lens and Abbe con- 

 denser, without the use of Blender. For unstained specimens, 

 oil immersion and the narrowed blender. 



When examining with low power objective, use a strong 

 ocular. When using high power objective use weak ocular. A 

 nose-piece will be found very useful, since it is sometimes neces- 

 sary to change the objective on the same field, and that insures 

 a great steadiness of the object. 



Great cleanliness is needed in all bacteriological methods ; but 

 nowhere more so than in the microscopical examination. 



The cover-glass should be very carefully washed in alcohol, 

 and dried with a soft linen rag. To remove the stains on the 

 cover-glasses that have been used, they should be soaked in 

 hydrochloric acid. 



Examination of Unstained Bacteria. As the coloring of bac- 



