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A MANUAL OF BACTERIOLOGY 



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- 

 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. 

 Afterwards the excess of the reagent or stain may be 



A 



B 



FIG. 21. Method of irrigation. 



washed away by running in water under the cover- glass 

 in a like manner. Care must be taken that no fluid gets 

 on to the upper surface of the cover-glass, which must 

 always be kept dry. The advantage of this method is 

 that it may be applied while the specimen is being examined 

 under the microscope, and the action of the reagent on a 

 particular cell or granule can, with a little care, be watched. 

 If the cells be large and it is desirable to avoid pressure 

 of the cover-glass, a fine hair or bristle may be so placed 

 on the slide that when the cover- glass is lowered one 

 edge rests on it. If the specimen has to be kept for 

 any length of time, the film of fluid will before long 

 evaporate and the preparation become dry. To prevent 

 this a ring of oil or vaseline may be painted round the 

 margin of the cover-glass so as to seal it to the slide. 



A simple method for keeping organisms under examina- 

 tion for a lengthened period of time, and of watching 



