204 BACTERIOLOGICAL EXAMINATION OF WATER. 



with Piorkowski's medium I have found that the appearances 

 presented by B. coli and B. typhosus are very variable. It is 

 very difficult to get the medium of a uniform composition, as 

 the time taken by different urines to become alkaline is not 

 constant. Also the characteristic forms of B. typhosus often 

 appeared in ordinary faintly alkaline gelatine, containing 33 

 per cent, gelatine. In 1896 Klie investigated the growth of 

 B. typhosus in media containing different percentages of 

 gelatine, and at different temperatures. He figured a very 

 characteristic colony of B. typhosus, growing at 19 21 C. in 

 3'3 per cent, gelatine, consisting of long threads growing out 

 from a central point. The appearances, however, changed 

 after twenty-four hours incubation, round centres appearing as 

 in the colonies of B. coli. Klie came to the conclusion 

 that the appearances of the colonies in dilute gelatine 

 media did not afford a sure means of diagnosis. The colony 

 figured by Klie, however, seems to me characteristic of 

 B. typhosus. None of the specimens of B. coli in my possession 

 ha,ve ever shown in 3'3 per cent, gelatine, after twenty-four 

 hours incubation at 19 to 21 C., a colony which at the centre 

 consisted of a point or fine line, from which long threads ran 

 out into the surrounding gelatine. The most motile forms of 

 B. coli under these conditions always showed a more or less, 

 thick circular dark-brown centre from which threads passed out 

 into the gelatine. 



Mayer has lately investigated the growth of B. typhosus in 

 Piorkowski's medium, and also in 3'3 per cent, neutral gelatine. 

 In order to overcome the difficulty introduced by the difference 

 in the time required to render urine alkaline, Mayer recommends 

 the addition of a twenty -four hours culture of Proteus vulgans 

 to the morning urine. If the urine be kept at 22 C. it will 

 become faintly alkaline within fifteen to twenty hours ; gelatine 

 (3'3 per cent.) and peptone are then added, and the medium 

 sterilised in current steam at 100 C. In this medium (which 

 has a neutral reaction) five forms of colonies are obtained > 

 according to Mayer ; the fifth form or group is characteristic of 

 B. typhosus, and consists of colonies which have no appre- 

 ciable centre, or simply a thick point or streak from which 

 ffagella pass off' either on one side only or from all sides. This 



