40 LABORATORY BACTERIOLOGY 



any change in color since inoculation. Observations similar to 

 those on the plain milk should also be made. 



{d) Glucose agar. Note the character and number of 

 colonies within the agar, and the presence, if any, of gas 

 bubbles. Are there few or many of them? 



(i) Bouillon containing sugars in test tubes. Note care- 

 fully the appearance of the bouillon, but especially its chemical 

 reactions as indicated by the litmus paper (26). 



(/) 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 (2) the closed branch of the fer- 

 mentation 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 

 absence of gas in the closed branch. Indicate the quantity 

 and note its rate of formation from time to time. Test the 

 reaction of the liquid with litmus paper. 



The fermentation tubes are also used to enable one to deter- 

 mine the quantity and kinds of gases produced and the aerobic 

 or anaerobic tendencies of the organism. See Exercises XXIII. 

 and XXIV. 



