1.98 BACTERIOLOGICAL EXAMINATION OF WATER. 



quantities of this solution, usually 0*1, 0*2, and 0'3 c.c. were 

 added to tubes containing 10 c.c. of nutrient broth. The tubes 

 were then incubated for twenty-four hours at 37 C., and if they 

 remained free from growth, gradually increasing quantities of 

 the water from two drops to 1 c.c. were added to the tubes 

 which were again incubated at 37 C. for from twenty-four to 

 seventy-two hours. All the tubes which showed any growth 

 were then plated out in gelatine ; the colonies which developed 

 were examined under a low power, and those resembling 

 B. typhosus were fished and sub-cultured in various media. 

 Tiemann and Gartner very often found that the typhoid bacillus 

 did not grow in broth containing O'lO and 0'15 percent, of car- 

 bolic acid, and Losener obtained similar results. Vincent recom- 

 mended the addition of h've drops of a 5 per cent, solution of 

 carbolic acid to the broth tubes, which were then incubated at 

 42 C. Ravitsch-Stcherba added O'l per 1000 of a-naphthol to 

 the nutrient medium. Losener did not obtain satisfactory results 

 with this method ; the surface colonies of B. typhosus were 

 green in colour, granular, raised in the centre, and not easily 

 recognised. Holz prepared a potato-gelatine medium, which 

 had an acid reaction, and ten grammes of the medium required 

 1*6 c.c. of deci-normal alkali to effect neutralisation. Eisner 

 added 1 per cent, of potassium iodide to the potato-gelatine ; 

 the advantage of this addition has been denied by many workers. 

 On the iodised potato-gelatine medium the B. typhosus grows 

 slowly, and at the end of forty-eight hours the colonies appear 

 as small, clear dots, like minute drops of water ; the B. coli, on 

 the other hand, shows much larger colonies of a dark-brown 

 colour. Unfortunately these appearances cannot be relied upon ; 

 the colonies of B. coli sometimes appear small and transparent 

 like those of B. typhosus. Also many liquefying organisms 

 develop on the medium, so that the plates cannot be kept very 

 long under observation when the water is seriously polluted. 

 The great advantage of the potato-gelatine is that it diminishes 

 the number of colonies which must be sub-cultured for further 

 study. Only the small transparent colonies need be " fished " ; 

 the large brown colonies can be at once excluded from the in- 

 vestigation. Uffelmann suggested that ordinary gelatine should 

 be exactly neutralised, and then O'Ol per cent, of pure carbolic 



