Report on the Bacteriology of Water. 399 



were well waters, and, as is well known, it is just this kind of water 

 which has most frequently been conclusively convicted of distribut- 

 ing typhoid fever. 



The above discoveries of the typhoid bacillus in natural waters 

 have, in almost all cases, been made not by means of the ordinary 

 method of plate cultivation, which affords little or no chance of a few- 

 typhoid bacilli being discovered amongst a host of common water 

 bacteria, the colonies of which generally grow with great rapidity 

 and not unfrequently cause rapid liquefaction of the gelatine, but by 

 special methods of treatment which have been devised to oppose the 

 proliferation of the water bacteria whilst not materially interfering 

 with the growth and multiplication of the typhoid bacilli, the latter 

 thus acquiring a large numerical preponderance, if not entirely 

 excluding the other forms present in the water. 



Unfortunately, these conditions which foster the growth of the 

 typhoid bacillus to the exclusion of the ordinary water bacteria are 

 equally propitious to other microbes which are invariably associated 

 with the typhoid bacillus, and which, in fact, resemble it so closely, 

 especially in morphological characters, that they may easily be mis- 

 taken for the typhoid bacillus, and it is this circumstance which 

 causes so much doubt to attach more especially to the earlier of thoso 

 alleged discoveries of the typhoid bacillus in potable water which are 

 recorded above. 



The particular micro-organism, which is especially liable to cause 

 confusion in this respect, is the so-called Bacillus coli com.rn.unis. This 

 organism was described by Escherich, and is found regularly in the 

 human intestinal tract and faeces, as well as in the excreta of other 

 animals. It is regarded as identical with the Bacillus neapolitanus 

 (Emmerich), and the " Faeces bacillus " described by Weisser, 

 whilst by recent experiments I have shown that it is closely 

 allied to, if not identical with, the Bacillus ethacetosuccinicus 

 previously described by me. In all cases, therefore, in which water 

 is supposed to have been infected with the dejecta of typhoid 

 patients, the B. coli communis may be expected also to be present. 

 In order, therefore, to ascertain definitely whether the typhoid 

 bacillus 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 it would be a desideratum to have some method which would, 

 whilst revealing the presence of the typhoid bacillus, effectually 

 eliminate or separate out its almost constant attendant, the B. coli 

 communis. Unfortunately, this is a consummation which has not yet 

 been realised in fact, for not only is the vitality of the B. coli com- 

 munis in water, as will be shown below, superior to that exhibited by 

 the typhoid bacillus, but in all attempts which have so far been made 

 to suppress the vitality of other organisms, and yet permit of the 



