462 BACTERIAL FLORA OF THE SYDNEY WATER SUPPLY. 



a year's artificial culture, but that is only to be expected. Any 

 rapid change in cultural character would have occurred before 

 the fourth crop. This was noted in a previous paper to be the 

 case with Bac. piscicidios bipolaris, the colonies of which in 

 gelatine differed greatly in the second and fourth crops. From 

 the fourth onwards, the type was fixed. Whether the differences 

 between the types of other authors and these organisms are 

 sufficient to warrant the formation of a new species, a new sub- 

 species, or merely to note the difference, is a matter of opinion, 

 and I leave it to other bacteriologists to accept my ruling or 

 otherwise as they think fit. I believe the formation of sub- 

 species is to be recommended, but for this the diffidences must 

 not be vital, nor yet must they be insignificant so far as the 

 diagnostic characters are concerned. In this a hard and fast 

 line cannot be drawn, since a character which helps the diagnosis 

 of one class of organism may be useless for another class. As an 

 example, the liquefaction of gelatine may be cited. This action 

 is of immense help to the bacteriologist and is used to distinguish 

 classes of bacteria, yet it is too well known that the power may 

 be gained or lost under laboratory conditions, and if this is the 

 case a similar change may be expected to occur under natui'al 

 conditions. 



The organisms which have been described were isolated upon 

 Abba's gelatine or dextrin-meat-agar. There are other media, 

 however, less commonly employed in bacteriology and used for 

 the purpose of suppressing such as have been obtained and per. 

 mitting the growth of others. In a future paper I hope to 

 describe the less commonly occurring bacteria isolated by the 

 employment of selective methods. 



