CO VER-SLIP PREPAEA TIONS. 137 



To stain the fixed cover-slip preparation it is taken 

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

 drops of a watery solution of fuchsin, gentian- violet, or 

 methylene-blue are placed upon the film and are allowed 

 to remain there 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, and the preparation is ready for exam- 

 ination. 



Another plan that is 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 examina- 

 tion with the microscope. This method is satisfactory 

 and time-saving, but must always be practised with care. 

 The staining fluid should always be carefully filtered be- 

 fore using, to rid it of insoluble particles which might be 

 taken for bacteria. If upon examination the preparation 

 proves to be of particular interest, so that it is desirable 

 to preserve it, then it is to 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 float 

 around its edges. It is then taken up with the forceps, 

 carefully deprived of the water adhering to it by means 

 of blotting-paper and then allowed to dry. When dry 

 it is mounted in xylol-Canada-balsam by placing a small 

 drop of the balsam upon the surface of the film, and 

 then inverting the slip upon a clean glass slide. It is 

 sometimes desirable to have the balsam harden quickly, 

 and a method that is commonly employed to induce this 

 is as follows : The slide, held by one of its ends between 



