1907.] Bacteria may be present in Ventilating Pipes, etc. 257 



180 gallons of surface water at the time. An emulsion of B. prodigiosus was 

 poured into the water and plates of nutrose-agar were then suspended as 

 shown in fig. 2. Twenty-four hours later the plates were removed and 





^Srfr 



Fig. 2. 



incubated at 22° C. for^'two days, when numerous colonies of B. prodigiosus 

 were found in all the plates. Control plates of nutrose-agar, exposed to the 

 air outside the pit, did not show any signs of the special organism used in the 

 experiment. 



These results show that bubbles rising through stagnant water may eject 

 bacteria, which will be carried away by currents of air passing over the 

 surface of the fluid. 



GROUP 2. — Experiments to determine whether Bacteria dried on the surfaces of 

 Pipes are likely to he separated and carried by Currents of Air passing, 

 through the System. 



The apparatus shown in fig. 3 was employed. Three 2-ft. lengths of 

 6-inch piping were laid on the ground and a rich emulsion of B. prodigiosus 



Fig. 3. 



