276 MICRO-ORGANISMS IN WATER 



those of a few other forms ; any colonies at all resem- 

 bling those of the typhoid bacillus must then be further 

 examined (1) microscopically; (2) by cultivation on 

 potatoes; (3) by inoculation into melted gelatine-tubes for 

 the gas-bubble test; (4) by cultivation in milk for coagula- 

 tion; and (5) by cultivation in broth for the indol-reaction^ 

 before a reasonably safe diagnosis of typhoid bacilli 

 can be made (see note p. 285.) 



A description of the B. coli communis, together with 

 some of the principal organisms which closely resemble 

 the typhoid bacillus, will be found in the tables at the 

 end of the book (see pp. 410-415). 



DETECTION OF KOCH'S COMMA BACILLUS IN WATER 



As in the case of the typhoid bacillus, so with that of 

 cholera, much difficulty is experienced in its recognition 

 amongst a number of other bacteria. To facilitate its 

 identification Schottelius 1 recommended the following 

 method : A small quantity of the choleraic dejecta is 

 mixed with twice its quantity of slightly alkaline 2 sterile 

 bouillon, and is then preserved at a temperature of from 

 30-40C. for twelve hours. At the end of this time an 

 extensive multiplication of the cholera bacillus takes 

 place on the surface of the liquid, a small quantity of the 

 pellicle often exhibiting under the microscope an almost 

 pure cultivation of the cholera bacteria. If the cultiva- 

 tion remains standing for two or three days, on the 

 other hand, only very few, or perhaps no cholera bacilli 

 will be found, the latter having been outnumbered by 

 the other organisms present. This method may of course 

 be applied in the case of waters suspected of harbouring 

 the cholera bacillus. 



1 Deutsclte med. Woch&nschrift, 1885, No. 14. 



- It is of the greatest importance that all the media employed in the 

 culture of the cholera bacilli should be very distinctly alkaline in reaction 

 (see p. 23). 



