86 General Bacteriology. 



EXERCISE LXXIII. TESTING DISINFECTING ACTION OF CHEMICALS. 



SUSPENSION METHOD. 



a. Make a culture of the organism to be studied in tubes of bouillon containing 5 cc. 



b. 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. 



COVER -GLASS METHOD. 



a. Make a bouillon culture of the organism to be studied and incubate at 38 C.for 

 24 hours. 



b. 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 (XLIII). 



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

 the desired time, then removed 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 (10%), 

 using B. coli. 



REFERENCES. A. 558; N. 518; P. 152; S. 158. 



