260 Maj. Horrocks. Conditions under ivhich" Specific" [Jan. 11, 



Further experiments on the same lines were then carried out with the 

 B. prodigiosus, an agar growth emulsified in water being added to the sewage. 

 Jhe same apparatus was used as in the previous experiments, the vertical pipe 

 being gradually lengthened by the addition of 2 -ft. lengths of 6 -inch piping. 

 The B. prodigiosus was recovered from the plates suspended 8 feet 9 inches 

 and 11 feet 9 inches above the sewage in the trap. 



It was thought that possibly the resistance produced by the passage of the 

 sewage through the trap might have caused the projection of the special 

 bacteria employed into the air contained in the vertical pipe. 



Accordingly, in the next series of experiments, the trap was removed and 

 the apparatus fitted up as shown in fig. 3. Plates of nutrose-agar were 

 suspended in the vertical pipe, and the sewage mixed with B. prodigiosus was 

 made to flow at a rate not exceeding 3 feet per second, through the horizontal 

 pipes, which were never more than half filled with the sewage. The special 

 organism was again recovered from plates suspended 11 feet 9 inches above 

 the sewage in the trap. 



As in all the above experiments, a very rich emulsion of the special 

 organism, such as would never be found under natural conditions, was added 

 to the sewage, it was determined to repeat' the 'experiments, employing only 

 1 c.c. of the emulsion, representing one-ninth oLthe .growth on an agar slope 

 after 48 hours' incubation at 22° C.,> to inoculate 4he sewage. The same 

 results were obtained as when the rich emulsion was' 'used.' 



It is evident from these experiments that special bacteria can be ejected 

 from flowing sewage independently of the resistance offered .to the flow by the 

 disconnecting trap. But as the plates were left' in the vertical pipe for more 

 than 24 hours, it is possible that the colonies in the plates might have been 

 derived from particles dried on the surfaces of the pipes. In order to 

 exclude this source of the bacteria, the experiments were repeated again, but 

 the plates were withdrawn immediately the sewage had ceased to flow, each 

 experiment only occupying 20 minutes. As before, colonies of B. prodigiosus 

 were found in all the plates, showing that they must have been produced 

 independently of dried particles carried by currents of air. As there were 

 very few bubbles visible to the naked eye in the flowing sewage, it is not 

 very probable that all the microbes found in the plates were ejected into 

 the air by the bursting of bubbles. I think it is possible that many of the 

 colonies were caused. by the ejection of minute infected droplets from the 

 flowing sewage. Gross splashing is out of the question, as the sewage was 

 flowing at a comparatively slow rate, and plates were found infected at a 

 height of 11 feet 9 inches above the surface of the fluid. 



The next series of experiments were undertaken to test the value of the 



