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Experiments made to determine the Conditions under which 

 " Specific " Bacteria derived from Sewage may be present in 

 the Air of Ventilating Pipes, Drains, Inspection Chambers 

 and Sewers. 



By Majok W. H. Horkocks, E.A.M.C. 



(Communicated by Colonel David Bruce, C.B., F.R.S., E.A.M.C. Received 

 January 11, — Read February 7, 1907.) 



Most sanitarians at the present time believe that when sewage is in a 

 putrefactive condition and gas bubbles rising through it are bursting at the 

 surface, bacteria may be carried into the air of drains and sewers. It is also 

 considered possible that when sewage has dried on the surfaces of pipes, 

 bacteria may be separated as dried particles and carried some distance by 

 currents of air passing through the pipes. 



The following experiments were designed to ascertain whether there are 

 any scientific facts on which to base these beliefs, and may be arranged in 

 three groups. 



GROUP 1. — Experiments to determine whether Specific Bacteria are ejected into 

 the Air by the bursting of Bubbles at the surface of Sewage. 



In the first series of experiments, sewage obtained from a main sewer in 

 Gibraltar was inoculated with a rich emulsion of B. prodigiosus and then 

 poured into a deep glass jar so as to form a layer at the bottom about 

 2 inches deep. At a height of 4 inches from the surface of the sewage two 

 Petri dishes containing nutrose-agar were fastened, the medium facing 

 upwards, to wire tripods, which were then firmly wedged in the bottom of the 

 dish. A glass cover was then put on the dish and the fluid gently shaken by 

 a horizontal movement, until a layer of bubbles formed on the surface of the 

 sewage. This procedure was followed at intervals for three days, the plates 

 were then taken out and incubated at 22° C. After seven days' incubation no 

 signs of the B. prodigiosus appeared. Only one colony composed of cocci 

 derived from the air was seen. This experiment was repeated again and 

 again, but invariably with negative results. 



The sewage was next inoculated with a rich emulsion of B. typhosus, and 

 litmus-lactose-nutrose-agar plates were fastened to the tripods. The dish was 

 shaken as before, the plates were then removed and incubated at 37° C. No 

 signs of B. typhosus or B. coli were observed after incubation for one week. 



