Simple Method of Staining 



147 



more convenient method is to wipe the glasses as clean as possible 

 with a soft cotton cloth, seize them with fine-pointed forceps, and 

 pass them repeatedly through a small Bunsen flame until it becomes 

 greenish-yellow. The hot glass must then be slowly elevated 

 above the flame, so as to allow it to anneal. This manoeuver 

 removes the organic matter by combustion. It is not expedient 

 to use covers twice for bac- 

 teriologic work, though if 

 well cleansed by immer- 

 sion in acid and washing, 

 they may subsequently 

 be employed for ordinary 

 microscopic objects. 



The fragility of the 

 covers and their likelihood 

 to be broken or dropped 

 at the critical moment, 

 make most workers pre- 

 fer to stain directly upon 

 the slide. The slide should 

 be thoroughly cleaned, 

 and if the material to be 

 examined is spread near 

 one end, the other may 

 serve as a convenient han- 

 dle. The slide is also to 

 be preferred if a number 

 of examinations are to be 

 made simultaneously or 

 for comparison, as it is 

 large enough to contain a 

 number of "smears. " 



SimpleMethodof Stain- 

 ing. — The material to be 

 examined must be spread 

 in the thinnest possible 

 layer upon the surface of 

 the perfectly clean cover-glass or slide and dried. The most conveni- 

 ent method of spreading is to place a minute drop on the glass with 

 a platinum loop, and then spread it evenly over the glass with the flat 

 wire. Should it be stained at once it would all wash off, so it must 

 next be fixed to the glass by being passed three times through aflame, 

 experience having shown that when drawn through the flame three 

 times the desired effect is usually accomplished. The Germans 

 recommend that a Bunsen burner or a large alcohol lamp be used, 

 that the arm describe a circle a foot in diameter, each revolution 

 occupying a second of time, and the glass being made to pass through 



Fig. 32. — Apparatus for keeping objects under 

 microscopic examination at constant tempera- 

 tures (Nuttall). 



