INFLUENCE OF DISINFECTANTS 123 



EXERCISE II 



We have now six flasks containing different solutions 

 of disinfectants. 



1. Place in each one of these flasks nine of the pre- 

 pared rods, three of which have been dipped in the 

 Staph. pyogenes aureus culture, three in the B. coli 

 culture, and three in the B. typhosus culture. 



2. Take three rods (one of each organism) out of 

 each flask after the lapse of half a minute, wash by 

 gently pouring sterile physiological salt solution over 

 them into a dish containing mercuric chlorid solution 

 i : 1000, and place each rod in a tube of sterile broth 



3. Repeat the proceedings of step 2 .with a second 

 series of rods after 2 minutes. 



4. Repeat again after 5 minutes with the remaining 

 series. 



5. Place all tubes (fifty-seven) in the thermostat. 

 Three of these tubes have not been dipped into any one 

 of the six flasks containing antiseptics, and are incubated 

 with the others as controls. 



6. Observe the results carefully on each of the four 

 successive days, and on the last day prove the relative 

 growth by making agar-plates with i c.c. of each culture, 

 and count the colonies after 24 hours. 



7. Tabulate the results, and state your conclusions. 



EXERCISE III. INFLUENCE OF SUNLIGHT 

 EXPERIMENT I 



1. Inoculate a flask containing 100 c.c. of sterile 

 water with B. coli. 



2. After thoroughly shaking, take i c.c. by means of 

 a sterile pipette, and plate in agar. Place the plate in 

 the thermostat. 



