MAKING COVER-GLASS PREPARATIONS 21 



EXERCISE VII 



MAKING AND STAINING COVER-GLASS PREPARATIONS, 

 AND FORMULAE FOR STAINING SOLUTIONS 



3d. Work for this Exercise. — Make 2 cover-glass prepa- 

 rations from each of. the cultures made in Exercise V. and stain 

 one of each with alka,line methylene-blue and the other with 

 carbol fuchsin. Describe the appearance of the bacteria and 

 make a drawing of a few individual bacteria from the prepara- 

 tions made from the agar culture. 



Preserve a cover-glass preparation mounted in balsam and 

 labelled to accompany notes. 



Prepare the staining fluids used in this exercise from the 

 formulse given. 



Read the paragraphs in the text-books on making and stain- 

 ing cover-glass preparations. 



31. Making Cover-glass Preparations. — (i) From bouillon 

 cultures. Place 2 clean cover-glasses on the tray. With the 

 loop remove a ^rop of the bouillon culture and spread it in a 

 thin layer over about two-thirds of the surface of the cover- 

 glasses. One loopful will ordinarily make from 2 to 4 prepara- 

 tions. Allow the liquid to dry on the cover-glasses in the air. 

 When dry, fix the bacteria to the cover-glasses by passing 

 them, film upward, three times through the middle of the 

 upper half of the gas flame. Each passage (complete circle) 

 should not occupy more than i second. After fixing, they are 

 ready for staining. (2) From cultures on solid media (agar, 

 gelatin, potato, serum, etc.). Place the cover-glasses on the 

 tray, and on the centre of each put a drop of sterile water or 

 bouillon. With the needle touch the surface growth of the 

 culture and then gently rinse the end of the needle in the liquid 

 on the covers. Spread the liquid on the covers as before. 



