EXAMINATION OF BACTERIA WITH THE MICROSCOPE. 27 



should be employed, but none of these appear exact, and one 

 soon acquires by practice an idea as to how long the manip- 

 ulation should take. Indeed, this varies with the character 

 of the preparation. The heat of the flame serves to dry the 

 bacteria upon the cover-glass and make them adhere per- 

 manently in position. It also aids in the penetration of the 

 staining dyes; but it is not sufficient, when applied" in this 

 mahner, to kill all kinds of bacteria, especially those containing 

 spores. After it has been passed through the flame three times, 

 the preparation may be stained with a solution of one of the 

 aniline dyes, as described below, and after washing in water 

 and drying may be mounted, face down, in Canada balsam 



Fig. g. — Kirkbride forceps for holding slides. 



upon a glass slide. It makes a suitable object to be examined 

 with the oil-immersion objective. 



The smear preparation may equally well be made directly 

 upon the glass slide. The fixation in the flame must then 

 occupy a longer time than with the small and thin cover-glass. 

 Such preparations have the advantage that several may be 

 made upon one slide, and that after staining them they may be 

 examined in cedar-oil, with the oil-immersion lens, without 

 the use of the cover-glass and Canada balsam. The forceps of 

 Kirkbride will be found convenient for staining on the slide. 

 Experiments performed in the writer's laboratory have shown 

 that the ordinary method of fixation in the flame, when ap- 

 plied to bacteria spread upon slides, has little effect on the 



