98 GENERAL MICROBIOLOGY 



Cultures. Cultures in milk, serum, etc., media. 



Method. 1. Prepare the cover-glass specimen directly 

 from the medium without the use of water. Spread and fix 

 in the usual manner. 



2. Flood the specimen side of cover-glass with glacial 

 acetic acid. 



3. Drain immediately without washing. A piece of 

 filter paper may be touched to the edge of glass to take 

 up surplus water and facilitate drainage. 



4. Stain with aqueous-alcoholic gentian violet for a 

 few seconds. 



5. Examine under the microscope. 



6. Wash, dry and mount, 



EXERCISE 34. METHOD OF MAKING IMPRESSION 

 PREPARATIONS 



Impression preparations (Klatschpraparat) are pre- 

 pared from isolated colonies of bacteria in order that their 

 characteristic formation may be examined by higher powers 

 than can be used with the living cultivation in situ. They 

 are prepared from plate cultivations. Young colonies of 

 Bad. anthracis produce beautiful impression preparations. 



Apparatus. Clean cover-glasses; clean slides; Novy 

 cover-glass forceps; dissecting needle; stain. 



Culture. Agar plate culture containing well-isolated 

 colonies of organism to be studied. 



Method. 1. Taking a clean cover-glass in the Novy 

 forceps, open the plate and rest one edge of the cover- 

 glass on the surface of the medium a little to one side of 

 the selected colony. 



2. Lower it carefully over the colony until horizontal. 

 Avoid any lateral movement or the inclusion of air bubbles. 



3. Press gently on the center of the upper surface of 

 the cover-glass with the points of the forceps to insure 

 perfect contact with the colony. 



