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



Old sewage, smelling strongly of sulphuretted hydrogen gas, was then placed 

 in the dish and the experiments were repeated as before. It was thought that 

 gas bubbles would form more readily in old than in fresh sewage ; this proved 

 to be the case, but the special organisms added to the sewage never appeared 

 in the plates. 



Soapy water from a lavatory basin was then inoculated with B. prodigiosus 

 and freely shaken in a glass bottle until it was permeated with bubbles ; the 

 fluid was then transferred to the glass dish, the plates fastened to tripods were 

 rapidly placed in situ, and the cover put on. Twenty-four hours elapsed before 

 all the bubbles dispersed, the plates were then taken out and incubated as 

 before, but no signs of the B. prodigiosus appeared. 



In the above experiments there were no air currents circulating above 

 the sewage, and the bacteria could only be ejected by the bursting of bubbles. 

 The results appear to show that independently of air currents, bacteria will 

 not be ejected to a height of 4 inches by the bursting of infected bubbles. 



The next series of experiments were made with the apparatus shown in 

 fig. 1. Plates of nutrose-agar were suspended by means of wire cages in the 



vertical pipe, the uppermost plate 

 being 9 feet above the water in the 

 trap. Soapy water, inoculated with an 

 emulsion of B. -prodigiosus, was shaken 

 up in a glass stoppered bottle until 

 the whole fluid was permeated with 

 bubbles, the contents of the bottle 

 were then poured into the trap until 

 it was filled. Under these conditions 

 currents of air passing up the vertical 

 pipe were able to carry bacteria 

 separated from the fluid by the burst- 

 ing of bubbles. The plates were 

 removed at the end of two hours and 

 incubated at 22° C. The result was 

 that colonies of B. prodigiosus ap- 

 peared in every plate at the end of 

 72 hours. 

 The last experiment of this series was made with a catch-pit on the storm- 

 water system of the town. Complaints having been made of foul odours 

 arising from the pit, the hinged cover was thrown back, and it was then seen 

 that bubbles were rising through the water retained in the pit as a result of 

 fermentation processes going on in the mud at the bottom. The pit contained 



Fig. 1. 



