MAKING COVER-GLASS PREPARATIONS 23 



EXERCISE VII 



MAKING AND STAINING COVER-GLASS PREPARATIONS, 

 AND FORMULA FOR STAINING SOLUTIONS 



33. 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 alkaline 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 

 labeled to accompany notes. 



Prepare the staining fluids used in this exercise from the 

 formute given (§ 37). 



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

 ing cover-glass preparations. See references and text-books 

 for various staining solutions that are sometimes used. 



33. Making cover-glass preparations, (a) From Iwuil/on 

 cultures. Place two clean cover glasses on the tray. With the 

 loop remove a drop of the bouillon culture and spread it in a 

 thin layer over about two thirds of the surface of the coA-er 

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

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

 air and, when dry, fix the bacteria to them 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 one second. After fixing they are 

 ready for staining, {b) From cultures on solid media (agar, 

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

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

 bouillon. Touch the surface growth of the culture with the 

 end of the needle and then gently rinse it in the liquid on 

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



