20 



waving the cover glass, to and fro, over a flame, at a height 

 of 6 or 8 inches. Care must be taken not to transfer too 

 much material to the drop of water, for in such cases the 

 cover-glass on subsequent staining will be found to be one 

 mass of bacteria. 



The cover-glass prepartion which has now been dried 

 in the air or over a flame, must be u fixed" before apply- 

 ing the staining solution. For this purpose, take hold of 

 the cover-glass with a narrow-pointed pair of forceps, 

 and pass it rapidly through the flame, from above down- 

 ward, keeping the specimen side up, away from direct 

 contact with the flame. If the exposure to the flame is 

 too long the bacteria may be so altered as to refuse to take 

 the stain subsequently, or at most poorly. On the other 

 hand, if not heated enough, the bacteria will readily wash 

 away on treatment with the dye, or with water. 



As soon as the fixed cover-glass is cool, and while still 

 holding it in the forceps, cover the specimens with the 

 dilute aniline stain. Allow this to act for the necessary 

 length of time (i ^ 1 min.) and then wash off com- 

 pletely by means of a syphon or bulb wash-bottle. Place 

 the cover-glass now on a piece of filter-paper, resting on 

 the right index finger, and rotate carefully till the lower 

 side is perfectly clean and dry. Now invert the specimen, 

 with the moist specimen side downward, onto a clean glass 

 slide. Sufficient water should be present to fill in the 

 space between the cover-glass and slide. Specimens 

 should never be examined dry. 



Place the slide thus prepared on the stage of the 

 microscope and first examine with the No. 7 objective and 

 subsequently with the ^ homogeneous oil-immersion 

 objective, in the same way as was done in examining 

 hanging drops. 



A good cover-glass should show the bacteria well 

 stained, not in masses, but separated from each other, and 

 evenly distributed over the entire cover-glass. If the 

 stained bacteria are seen to move about it is due to insuf- 

 ficient fixing in the flame. 



