QUALITATIVE BACTERIOLOGICAL ANALYSIS. 213 



crumpled appearance, and the bacillus will show diminished 

 resistance to carbolic acid. This last fact is of importance in 

 relation to Parietti's test for the isolation of the B. typhosus 

 from water. The behaviour of the B. coli in sterile sewage was 

 then studied. After immersion for forty-two days in sewage 

 filtered through a Berkefeld bougie it was found that the 

 production of indol was delayed and the bacillus seemed less 

 resistant to carbolic acid, for whereas the original B. coli grew 

 well in 0'2 per cent, carbolic acid broth after twenty-four hours 

 incubation at 37 C., the bacillus from the sewage showed no 

 growth in 0'15 per cent, carbolic acid broth after twenty-four 

 hours at 37 C., but grew well in 0*1 per cent, carbolic acid 

 broth. The action of B. coli on B. typhosus when growing side 

 by side in sterile sewage was next tested. A fresh twenty-four 

 hours culture of B. coli was added to test tubes containing sterile 

 sewage in which B. typhosus had been planted out twenty-four 

 hours earlier. After fourteen days at the laboratory temperature, 

 loopfuls were removed and plated in Holz's potato-gelatine, 

 and rubbed over the surface of ordinary gelatine solidified in 

 Petri dishes. No signs of the B. typhosus could be detected in 

 these plates. The experiment was repeated again, but in a 

 slightly different manner. A large loopful of a twenty-four 

 hours agar growth of B. typhosus was added to 10 c.c. of sterile 

 sewage and incubated at 37 C. for forty-eight hours ; the sewage 

 was then found quite opaque, and a loopful plated out in gelatine 

 produced innumerable colonies of the typhoid bacillus. A very 

 small quantity of an agar growth of B. coli was now introduced 

 into the mixture of sewage and typhoid bacilli, and the tube 

 preserved at the laboratory temperature. The B. typhosus was 

 isolated from the tube up to the end of five days, but after this 

 it could not be detected. Working on the same lines with B. 

 fluorescens Jiquefaciens I was not able to isolate the typhoid 

 bacillus after the seventh day. These experiments appeared to 

 show that the presence of B. coli and B. fluorescens liquefaciens 

 had a marked influence on the existence of the typhoid bacillus 

 in sewage. At the same time I was conscious that the results 

 were by no means conclusive, as some typhoid colonies mio-ht 

 have been present on the gelatine plates and yet escaped atten- 

 tion owing to the large number of colonies of B. coli which 



