ESSENTIALS OF BACTERIOLOGY 



sists of a system of lenses which can be dipped into a drop of 

 cedar-oil placed upon the cover-glass, and which is then ready 

 for use. 



Abbe's Condenser. The second necessary adjunct is a 

 combination of lenses placed underneath the stage, for 

 bringing wide rays of light directly under the object. It 



serves to intensify the colored pic- 

 tures by absorbing or hiding the 

 unstained structure. 



This is very useful in searching 

 a specimen for bacteria, since it 

 clears the field of everything that 

 is not stained. It is called Abbe's 

 condenser (Fig. 9). Together with it is usually found an in- 

 strument for shutting off part of the light a blender or dia- 

 phragm (Fig. 10). When the bacteria have been found, and 

 their relation to the structure is to be studied, the "Abbe" is 

 generally shut out by the iris blender, and the structure 

 comes more plainly into view. A white light (daylight or a 



Fig. 9. Abbe's condenser. 



Fig. 10. Iris blender. 



Welsbach burner) is best for bacterial study: use the plane 

 mirror with the condenser. 



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 



