126 BACTEEIOLOGY. 



To stain the fixed preparation it is taken 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 with blotting-paper, 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 

 blottiug-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 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 

 from the slide by allowing water to flow around its 

 edges. It is then taken up with the forceps, carefully 

 deprived of the water adhering to it by means of blot- 

 ting-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. 



Impeession Cover-slip Peepaeations. — The im- 

 pression preparations differ in value from the ordinary 

 cover-slip preparations ouly in one respect : they present 

 an impression of the organisms as they were arranged in 



