72 GENERAL BACTERIOLOGY 



exercise 44. effect of chemicals on bacteria. 



General Directions. 



a. Inoculate three tubes containing 10 cc. of sterile bouillon, with 

 three loopfuls of a 24-hour old broth culture of organism to be 

 studied. 



6. Add 0.1 ce. of a 5% solution of carbolic acid to one tube (No. 

 1) ; 0.6 cc. to another (No. 2) ; and 2 cc. to the third (No. 3). 



c. Two hours later transfer three loopfuls from each tube to 

 sterile bouillon and incubate all of the tubes at 38° C. 



d. The carbolic acid does not prevent growth in No. 1 or its sub- 

 culture. In No. 2 no growth, but abundant in its sub-culture (acts 

 as an antiseptic). In both No. 3 and its sub-culture no growth (acts 

 as a disinfectant). 



Keperences. F. 81 ; L. & N. 37 ; L. 107 ; McF. 45. 

 Special Directions. Use B. coli. 



EXERCISE 45. 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 organism. 



5. 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, 



Eeferences. F. 60 ; L. & N. 41 ; L. 180 ; M. & R. 19 ; McF. 212 ; 

 P. 151. 



Special Directions. Use B. suhtilis and an anaerobe. Sketch. 



exercise 46. 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). 



