ESSAYS ON BACTERIOLOGY. 125 



liave brought the bacteiia within the reach of our 

 vision. A brief description of this part of bacterio- 

 logical work will therefore not be amiss, especially 

 since it has become of everyday utility. 



In preparing for the microscopic examination 

 of bacteria the following steps are taken with 

 all fluid or semi-fluid specimens. A minute por- 

 tion of an artificial culture or of the microbe- 

 ■containing material is spread in a very thin layer 

 upon a slide or cover glass. This is allowed to 

 dry in the air, or is dried by gentle heating. 

 When dry, it is passed, prepared-side upward, three or 

 four times through the clean flame of a spirit lamp or 

 Bunsen burner. This coagulates uniformly the al- 

 bumen and cements the specimen to the glass, and it 

 is now ready for the important process of staining. 

 If the bacteria are to be inspected in their natural con- 

 dition, unstained, they are placed in a drop of distilled 

 water and immediately examined. Thus seen, the 

 germs are almost or quite colorless. It is therefore 

 customary to give to them an artificial coloring in 

 order to render them more visible and their outlines, 

 and to some extent their structure, more distinct. 

 For this purpose solutions of the basic anilin dyes are 

 generally used. Among these are two which have 

 "been settled upon as answering all ordinary demands. 

 These are a red and a blue dye, named respectively 

 fuchsin and methyl blue. Solutions of these colors 

 are made in water or alcohol, or in both, and to these 



