44 LABORATORY GUIDE IN BACTERIOLOGY 



Method of making stained preparations — 



1. Clean and flame a cover-slip, or, if preferred, 

 a slide may be used for this purpose. Cover-slips, if 

 handled by the fingers, should be held by the edges. Use 

 as much as possible the forceps made for that purpose. 

 After handUng the forceps they should be sterilized in the 

 flame. 



2. Place one loopful of water on the cover-slip. 



3. Take the minutest quantity of the colony or cul- 

 ture on a platinum needle and mix gently with water 

 until faintly cloudy. Burn the remainder of the culture 

 off the needle. 



4. Spread over the cover-slip by two or three sweeps 

 of the needle. The water should spread easily and not 

 run together. If this takes place, the cover-slip has not 

 been cleaned sufficiently. 



5. Dry by moving high over the flame. 



6. Pass three times back and forth through the flame 

 rapidly. This process precipitates albuminous matter 

 and causes the bacteria to adhere firmly to the glass. 



7. Cover with stain for 10-15 seconds. 



8. Wash in water and examine. If satisfactory: 



9. Float the cover-slip off the slide with water. Blot 

 with filter-paper, dry in the air or high over the flame, 

 and mount in Canada balsam. 



10. Label and preserve this preparation. 



Try to avoid the mistake, made by most beginners, 

 of taking too much growth on the needle. For hanging- 

 drop preparations less material should be used than for 

 a stained preparation. 



