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A MANUAL OF BACTERIOLOGY 



isms. This may be done by placing a droplet of sterile 

 water, broth, or salt solution on the slide, inoculating 

 with a trace of the material or growth, and covering with 

 a cover-glass. The action of stains and reagents on the 

 organisms may be observed by the irrigation method. A 

 drop of the stain or reagent (c, Fig. 23), is placed on the 

 slide, A, just in contact with one margin of the cover- 

 glass, B, and is drawn through the preparation by means 

 of a small piece of filter-paper, D, placed on the other 

 side, a torn margin touching the film of fluid at one edge 

 of the cover-glass. 



The filter-paper absorbs the fluid from under the cover- 



B 



FIG. 23. Method of irrigation. 



glass, leaving the cells and other particles behind, and at 

 the same time the reagent on the opposite side flows under 

 the cover-glass to take the place of the absorbed fluid. 

 The excess of the reagent or stain may afterwards be 

 washed away by running in water under the cover-glass 

 in a like manner. The upper surface of the cover-glass 

 must be kept dry and free from fluid. This method may 

 be applied while the specimen is being examined under 

 the microscope, and the action of the reagent on a par- 

 ticular cell or granule can, with a little care, be observed. 

 If it be desired to avoid pressure of the cover-glass, a 

 fine hair or bristle may be arranged on the slide so that 

 one edge of the cover-glass rests on it. In order to prevent 

 evaporation, if the preparation has to be observed for 



