QUALITATIVE: BACTERIOLOGICAL ANALYSIS. 211 



but the sewage was now kept at 22 C. instead of 37 C. The 

 results obtained were as follows : 



Immediately after 1 



f . Y 22o colonies developed from one loopful of sewage. 



After 24: hours . 250 



68 . . 140 



5 days . 48 



.7 . 13 



13 . . 



Experiments made with B. coli showed that this organism 

 was able to grow and multiply abundantly in sewage sterilised 

 by heat when incubated at 37 C., and that it could be cultivated 

 for several generations. After growing for four days in sewage 

 the B. coli still retained its powers of coagulating milk, of 

 forming gas-bubbles in gelatine and producing indol in broth. 

 As a result of these experiments, Laws and Andrewes concluded 

 that sewage, even in the absence of the normal micro-organisms 

 which it contains, is an unfavourable medium for the growth of 

 the typhoid germ, whereas the colon bacillus can grow and 

 multiply freely in it. Further experiments were then made 

 in order to gain some idea of the influence which various non- 

 pathogenic bacteria normally present in sewage would exert on 

 the life and growth of the typhoid bacillus when growing side 

 by side with it. Organisms were selected which did not grow 

 well at 37 C., viz., B. fluorescens liquefaciens, B. albus putidus, 

 B. fluorescens stercoralis, and B. cloacae fluorescens. The follow- 

 ing conclusions were arrived at : 



The presence of certain non-pathogenic organisms commonly 

 present in sewage appeared to influence the extinction of the 

 B. typhosus. Of the four organisms tested B. fluorescens 

 stercoralis alone seemed to have any marked effect upon the 

 vitality of B. typhosus, and this effect was practically absent 

 when other organisms were present at the same time. The 

 mixture of the four non -pathogenic bacteria had no effect in 

 hastening the extinction of B. typhosus ; indeed, the reverse 

 appeared to be the case. My own experiments at Netley gave 

 somewhat different results from those obtained by Laws and 

 Andrewes. The experiments were performed as follows : 



A specimen of sewage obtained from Yeovil was (a) placed 



