136 GENERAL BACTERIOLOGY 



EXERCISE 73. TESTING DISINFECTING ACTION OF CHEMICALS. 



SUSPENSION METHOD. 



a. Make a culture of the organism to be studied in tubes of 

 bouillon containing 5 cc. 



&. Incubate at 38 C. for 24 hours. 



c. Add to this an equal amount (5 cc.) of the disinfectant to be 

 tested, of double the required strength. 



d. At the end of 5, 10, 20, 40 and 60 minutes make agar rolls, 

 using two or three loopfuls of the mixture for each roll. 



e. In this way determine the time of exposure necessary to kill 

 the organism used. 



/. Test in this way the value of corrosive sublimate (1:1000) 

 and Lysol (5%), using B. coli or M. pyogenes.vsx. aureus. 



COVER-GLASS METHOD. 



a. Make a bouillon culture of the organism to be studied and 

 incubate at 38 C. for 24 hours. 



6. By means of a burette, pipette, or loop, place the same sized 

 drop on each of several sterile cover-glasses and dry as directed in 

 the experiment on desiccation (43). 



c. When the cover-glasses are dry, they are to be immersed in 

 the disinfectant for the stated periods of time; then removed, 

 washed in sterile water and transferred to tubes of melted agar 

 which are then made into rolls. 



d. Test by this method carbolic acid (5%), alcohol (95%) and 

 formaldehyde (4%) or formalin (10%), using B. coli. 



REFERENCES. A. 611 ; McF. 249 ; N. 518 ; P. 152 : S. 158. 



