COVER-SLIP PREPARATIONS. 171 



immersed in a mixture of equal parts of absolute alco- 

 hol and ether for about 15 minutes. At the end of 

 this time it may be removed and stained. The advan- 

 tage of this method is that there is less distortion and, 

 as a rule, less precipitation (or, perhaps better, no char- 

 ring) of extraneous matter. When fixed, staining is 

 usually a simple 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 ex- 

 amination. 



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 exam- 

 ination with the microscope. This method is satis- 

 factory and time-saving, but must always be prac- 

 tised 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 exami- 

 nation the preparation proves of particular interest, 

 so that it is desirable to preserve it, then it may be 

 mounted permanently. The drop of immersion oil 



