124 



PLANTS WITHOUT CHLOROPHYLL 



Prohleni 107: To determiiie the most effective disinfectants. 



Materials. — Use tubes of bouillon containing different strength 

 solutions of formalin, lysol, iodine, carbolic acid, and bichloride 

 of mercury. 



Method. — Expose all tubes unplugged to air, having previously 

 inoculated each tube with germs from a Petri dish culture. Num- 

 ber and label tubes. 



To tube 1 add 1 drop formalin. 



2 add 5 drops formalin. 



3 add 1 drop lysol. 



4 add 3 drops lysol. 



5 add 1 drop iodine. 



6 add 5 drops iodine. 



7 add 4 drops carbolic acid. 



8 add 10 drops carbolic acid. 



9 add 1 drop bichloride mercury solution. 

 10 add 5 drops bichloride mercury solution. 



Observations. — Tabulate daily for a week or more the results 

 for the contents of each tube on a table as shown below. 



Conclusion. — 1. Which of the above is the best disinfectant? 



Why do you answer 

 as you do ? (Remem- 

 ber that according to 

 definition an antisep- 

 tic may retard the 

 growth of bacteria 

 but will not of neces- 

 sity kill them ; a ger- 

 77iicide destroys all 

 bacteria if used prop- 

 erly; while a disinfect- 

 ant is a solution used to kill disease germs, usually in the excreta 

 of sick people.) 



2. Using the data from the last two problems, classify the 

 materials used, as antiseptics, germicides, or disinfectants. Give 

 reason for each. 



