etc. 



261 



1907.] Bacteria may be present in Ventilating Pipes, 



disconnecting trap as a means of protecting a house drainage system from 

 specific bacteria present in the air of. the sewer into which the house drain 

 discharges. 



The apparatus employed is shown in fig. 5. It was a combination of the 

 .arrangements used in the experiments already described. The straight run 

 «of piping, with the vertical pipe attached to it, represents the sewer and an 

 attached ventilating pipe ; joining the sewer is the house drain, the air in 

 which is separated from that in the sewer by the usual disconnecting trap. 

 The vertical pipe above the trap represents the air inlet or outlet, as the case 

 may be, of the house drainage system. Plates of nutrose-agar were suspended 

 in both vertical pipes. . Sewage inoculated with B. prodigiosus was then 

 allowed to flow at a rate not exceeding 3 feet per second through the pipes 

 representing the sewer. The flow of sewage was continued for half an hour 



Fig. 5. 



Fig. 6. 



on two successive days ; the plates were then withdrawn and incubated at 

 22° C. Colonies of B. prodigiosus were found in the plates placed in the 

 ventilating pipe of the sewer, but none were present in the plates placed in 

 the ventilating pipe above the disconnecting trap. 



The experiment was repeated again, but during the flow of the infected 

 sewage through the sewer the disconnecting trap of the house system was 

 repeatedly flushed with 3 gallons of sewage. It was thought that during the 

 flushing of the trap, microbes in the sewer air might possibly enter the house 

 drainage system. This never occurred, the plates on the house side of the 

 disconnecting trap never showed any colonies of B. prodigiosus. 



The vertical trap was then removed and the apparatus arranged as shown 

 in fig. 6. 



Inoculated sewage was made to flow through the sewer as before, and 

 every five minutes a 3-gallon flush was passed through the house drain. 

 Under these conditions colonies of B. prodigiosus appeared in the ventilating 

 pipe of the house system as well as in that of the sewer. These results show 



