THE EXAMINATION OF CULTURES 49 



75. "Work for this exercise. Examine and describe the 

 cultures made on the special media in Exercise XL 



Examine the bacteria on the potato culture microscopically 

 (i) in the fresh condition (hanging-drop preparation) and (2) 

 in a stained (carbo-fiichsin) cover-glass preparation. Describe 

 the appearance of the bacteria (§ 35). Examine the fermen- 

 tation tubes and indicate the quantity of gas. 



76. A few points to be observed in studying cultures on 

 special media, (a) Potato. Note carefully the extent and 

 color of the growth and its consistence. 



{b) Milk. Note whether or not the general appearance and 

 odor of the milk have been changed, and observe whether the 

 casein has been coagulated, giving a firm, solid coagulum, or 

 precipitated. Is the coagulum covered with a liquid (serum)? 

 if so, is it clear or milky? Is there any appearance suggestive 

 of saponification? Determine its consistence, chemical reac- 

 tion as indicated by litmus paper (§ 27), and give as descriptive 

 a name as possible to its odor. 



{c) Litmus milk. Note especially whether there has been 

 any change in color since inoculation. Observations similar 

 to those on the plain milk should also be made. 



{(t) Glucose agar. Note the character and number of col- 

 onies within the agar, and the presence, if any, of gas bubbles. 

 Are there few or many of them? 



{e) Boicillo?i containing sugars in test tubes. Note carefully 

 the appearance of the bouillon, but especially its chemical 

 reactions as indicated by the htmus paper (§ 27). 



(_/) Bouillon containing sugars in fermentation tubes. Ob- 

 serve the character of the growth in each tube (whether the 

 liquid is faintly or heavily clouded, turbid, contains flakes, etc.), 

 ■ — in (i) the open bulb and in (2) the closed branch of the 

 fermentation tube. Note the presence or absence of a mem- 

 brane on the surface of the liquid in the open bulb. Is there 

 a sediment in the bottom of the tube? If so, describe its 

 general appearance and consistence. Note the presence or 



