268 MICRO-OKGANISMS IN AVATER 



differentiation is a matter of extreme difficulty. The 

 particular microbe which has given rise to so much 

 confusion is the so-called B, coli communis (see p. 411). 

 This organism was described by Escherich, and is found 

 regularly in the intestinal tract as well as in human 

 f^ces, also in the excreta from animals, and is regarded 

 as identical with the Bacillus neapolitanus of Emmerich 

 and the Fa3ces-bacillus described by Weisser. In all 

 cases, therefore, where water is supposed to have been 

 infected by the f^ces of typhoid patients the B. coli com- 

 munis may be expected also to be present. This or- 

 ganism is in fact frequently found in great numbers in 

 polluted streams, as well as in well-waters into which 

 the drainage from dung-heaps has penetrated, whilst in 

 pure waters it is but rarely met with. Thei:"efore5 in 

 order to ascertain definitely whether the typhoid bacillua 

 is present in any given water, care must be taken that, 

 the B. coli communis is not mistaken for the former, and 

 to guard against this some method must be adopted 

 which will, whilst revealing the presence of the typhoid 

 bacillus, effectually eliminate or separate out its constant 

 attendant, the B. coli communis. Unfortunately this 

 is a matter of extreme difficulty, for the vitality of the 

 B. coli communis in water is superior to that exhibited 

 by the typhoid bacillus ; moreover, in all attempts which 

 have so far been made to suppress the vitality of other 

 organisms and yet permit the development of the latter, 

 the B. coli communis has shown itself to be possessed 

 of greater powers of resistance than the typhoid bacillus 

 itself. Hence, although the addition of various chemical 

 substances msij effectually destroy or retard the growth 

 of other organisms, yet the B. coli communis survives 

 and remains present along with the typhoid bacillus ; 

 indeed, in many cases it has been proved that such ad- 

 ditions have destroyed the typhoid bacillus and left the 



