50 General Bacteriology. 



EXERCISE XLV. RELATION TO OXYGEN. 



GENERAL DIRECTIONS. 



a. Pour a tube of melted agar into a sterile Petri dish, and when the medium has 

 hardened make several parallel streaks with a platinum loop charged with an aerobic or- 

 ganism. 



b. Sterilize a piece of mica or a cover- glass, by passing it several times through the 

 flame and place this over several of the streaks. This is to shut out the air and should 

 therefore be in perfect contact with the medium. 



c. Make another plate in the same way using an anaerobe. 

 REFERENCES. F. 60; L. & N. 95; L. 180; McP. Chap. VIII. 

 SPECIAL DIRECTIONS. Use B. siibtilis and an anaerobe. 



EXERCISE XLVI. EFFECT OF DIRECT SUNLIGHT. 



GENERAL DIRECTIONS. 



a. Make an agar plate of the organism to be studied (seeding rather thickly). 



b. When agar has thoroughly set, invert the Petri and paste on under side a piece of 

 black paper from which has been cut out a number of letters, e. g., student's initials. 



c. Expose this dish, paper side up, to the direct sunlight for a number of hours 

 (4-6). 



d. Remove the paper and incubate. 



REFERENCES. F. 71; L. &N. 101; L. 77; McF. 46; S. 151. 



SPECIAL DIRECTIONS. Use B. prodigiostis (Ehrenb.) Fluegge or B. typhosus. 



EXERCISE XLVII. DETECTION OF GAS (Shake Culture). 



GENERAL DIRECTIONS. 



a. Melt a tube of glucose agar (or gelatin) and inoculate with a gas-producing 

 organism. 



b. Thoroughly mix and solidify quickly by placing in ice water. 



c. Incubate over night. 



REFERENCES. L. & N. 153; M. & R., 85. 



SPECIAL DIRECTIONS. Use B. coli; incubate. Make sketch. 



EXERCISE XLVIII. QUANTITATIVE ANALYSIS OF GAS (Fermentation Tube). 



GENERAL DIRECTIONS. 



a. Inoculate the open arm of a fermentation tube with a gas-producing organism. 



b. Incubate at 38 C. 



c. By frequent observations determine: 



1. Whether growth takes place in the open or closed arm, i. e., whether it is aero- 

 bic or anaerobic. 



^2. The rapidity and total amount of gas formation. Use gasometer. (Plate I. B.) 

 3. Kinds of gas. When the culture has ceased producing gas, completely fill the 

 open arm with a 2 % solution of sodium hydrate ; place the thumb over the mouth of the 

 tube and thoroughly mix the Na OH with the gas in the closed arm, then without remov- 

 ing the thumb return the gas to the closed arm, remove the thumb, when the medium 

 will rise in the closed arm to take the place of the absorbed CO 2 . Measure. The re- 



