200 Specific Examples of Slide Making 



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143 



Figs. 142 and 143. Good and bad bacterial smears. Fig. 143 shows properly distrib- 

 uted bacteria in the smear. Fig. 142 is the result of applying too heavy a smear on a 

 dirty slide. 



the flame. The actual temperature should not exceed about 80° C, and it is 

 customary to hold the slide smear downward as it passes through the 

 flame. Care must be taken that the slide is dried before it is thus quickly 

 flamed or, of course, the bacteria will burst and be worthless. 



On the flamed and dried smear is placed a drop of the selected stain, 

 leaving this in place for about 30 sec. The time is not critical, and any 

 time between % and 1 min is perfectly satisfactory. It will be noticed 

 that the stain frequently evaporates slightly, leaving a greenish film on 

 the surface, and it is, therefore, better to wash it off with a jet from a wash 

 bottle than to rinse it oft. This jet should be directed from the fine orifice 

 of the wash bottle at an angle of about 30° to the slide and should be 

 intended to hit the edge of the drop. The jet will instantly lift off and float 

 away the surface film, as well as wash excess stain out of the prepara- 

 tion. The preparation is now permitted to dry. When dry, it may be 

 touched with immersion oil and examined under the oil-immersion lens. 

 If it is desired to maintain this specimen permanently, it may also have 

 a drop of Canada balsam placed on top of it and a very thin coverslip 

 pressed into position. These specimens, however, are so easy to prepare 

 that it is rarely necessary to preserve them permanently. The dried 

 smear, if kept free from dust, may be preserved for as long as a year 

 without further preparation. 



