44 



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 



