128 BACTERIOLOGY. 



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 dry- 

 ing 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 examination. 



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 stainiaig fluid should always be carefully 

 filtered before using, to rid it of insoluble particles 

 which might mislead the examiner into mistaking them 

 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 flow around its edges. It is then taken up 

 with the forceps, carefully deprived of the water adher- 

 ing 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 com- 



