262 Maj. Horrocks. Conditions under which " Specific" [Jan. 11,. 



that a disconnecting trap prevents microbes present in the sewer air from 

 passing into the house drainage system. 



The next series of experiments were made with actual drainage systems. 



In the first experiment a newly laid system of a house in the town was 

 tested by suspending plates in the junction and disconnecting chambers. A 

 plate was also fastened in front of the air inlet of the system, the air inlet 

 being provided with a mica valve. An emulsion of B. prodigiosus was placed 

 in the pan of the w.c. of the house, which was then flushed out. The plates 

 were removed 24 hours later and incubated, with the result that colonies of 

 B. prodigiosus were found in every plate. " Air " plates exposed showed no< 

 signs of the special organism used in the experiment. 



The second experiment was made at the military hospital, plates being 

 suspended in the top of a 6-inch ventilating pipe connected with a w.c. in 

 the basement. The plates were 50 feet above the ground level. A rich 

 emulsion of B. prodigiosus was placed in the pan of the w.c, and the contents 

 were then flushed in the usual manner. At the end of 24 hours the plates, 

 were removed and incubated for 48 hours, when all the plates were found 

 studded with colonies of the special organism. 



The third experiment was made in connection with the drainage at tha 

 east end of the Centre Block of the military hospital. At the north-east, 

 corner of the block there is a ventilating soil pipe, 6 inches in diameter,, 



West 



True North 



Europa sewer 

 East 



receiving the contents of a row of w.c.'s placed in an annexe on the first floor 

 of the hospital. The soil pipe is connected by a 6 -inch drain to a discon- 

 necting chamber (B), which is 10 feet deep, and discharges its contents by a 

 short drain into a 9 -inch sewer, running along the Europa Road. At th& 



