COVER-SLIP PREPARATIONS. 155 



that there is less distortion and, as a rule, less precipitation 

 (or, perhaps better, no charring) of extraneous matter. 



The majority of bacteria with which the beginner will 

 have to deal stain readily with watery solutions of any 

 of the basic aniline dyes, such, for instance, as fuchsin, 

 methylene-blue, or gentian-violet. 



To stain the fixed cover-slip preparation, it is taken 

 , by one of its edges between forceps, and a few drops of 

 a watery solution of either of the dyes named are placed 

 upon the film and allowed to remain twenty to thirty 

 seconds. The slip is then carefully rinsed in water, and 

 without drying is placed bacteria down upon a slide ; the 

 excess of water is taken up by covering it with blotting- 

 paper and gently pressing upon it, after which the 

 preparation is ready for examination. 



Another plan sometimes used is to bring the slip upon 

 the slide, bacteria down, without rinsing off the staining- 

 fluid ; the excess of fluid is removed with blotting-paper 

 and the preparation is ready for examination with the 

 microscope. This method is satisfactory and time-saving, 

 but must always be practised with care. The staining- 

 fluid should always be filtered before using, to rid it of 

 insoluble particles which might be taken for bacteria. 



If upon examination the preparation prove of particu- 

 lar interest, so that it is desirable to preserve it, then it 

 may be mounted permanently. The drop of immersion 

 oil is to be removed from the surface of the slip with 

 blotting-paper, and the slip loosened, or rather floated, 

 from the slide by allowing water to flow around its 

 edges. It is then taken up with forceps, carefully de- 

 prived of the water adhering to it by means of blotting- 



