38 



a hanging-drop preparation, and (2) stained cover-glass 

 preparations. Stain a preparation with alkaline methylene- 

 blue, one with carbol fuchsin, and one with an aqueous 

 solution of methyl-violet. Make a careful comparison of 

 the three preparations and note any difference in the appear- 

 ance of the bacteria or in the degree of intensity of the 

 stain. Preserve as a permanent specimen, to accompany the 

 notes, a preparation stained with each of the dyes. 



Prepare the aqueous solution of methyl-violet (§ 33). 



§ 56. The inoculation of glucose agar to determine 

 the power of the organism to produce gas. Boil the tube 

 of glucose agar in an open water bath until it is liquefied, then 

 cool it down to a temperature of 45° C. and inoculate it with 

 a loopful of the culture, carefully stir the agar with the loop, 

 after which .solidify the agar as quickly as possible. Isabel 

 and stand in the incubator. 



EXKRCISE XII. 

 THE EXAMINATION OF CULTURES ON SPECIAL MEDIA. 



§ 57. Explanatory note. As certain of these media are 

 used to determine the effect of the bacteria upon them it is 

 important to observe very carefully not only the appearance 

 of the growth of the bacteria, but also their effect, if any, 

 upon the medium upon or in which they are growing. This 

 is especially noticeable in the milk, litmus milk and .sugar 

 bouillon cultures. The changes here are largely due to the 

 action of the bacteria on the sugars or their power to pro- 

 duce alkali. 



§ 58. General Directions. Examine and describe the 

 cultures made on the special media in Exercise XI. 



Examine the bacteria on the potato culture microscopically 

 (i) in the fresh condition (hanging-drop preparation), and 



