DETECTION OF PATHOGENIC BACTERIA IN WATER 271 



violet have been added. The typhoid colonies assume a 

 blue colour, which becomes more intense with their age 

 and is finally of a much deeper tint than the surround- 

 ing gelatine. 



By means of this gelatine Uffelmann states that he 

 was able to so far eliminate other organisms that a 

 water, from which by using the ordinary gelatine 12,500 

 colonies were obtained, when tested by this special pro- 

 cess only exhibited nineteen. From another sample, 

 instead of 180, only eleven colonies appeared on the 

 plate, and out of these Uffelmann states that six were 

 those of the typhoid bacillus, being distinguished by the 

 characteristic blue colour which they exhibited. Dun- 

 bar, however, has shown that this gelatine is very pre- 

 judicial to the development of the typhoid bacillus, in 

 many cases no growth whatever appearing on the plates, 

 whilst when the B. coli communis was experimented 

 with it was found that they appeared abundantly, pre- 

 senting the same blue colour as the typhoid colonies, 

 although somewhat retarded in their growth. Dunbar 

 further ascertained that ~the amount of citric acid pre- 

 scribed by Uffelmann was altogether in excess of that 

 which the typhoid bacilli were capable of standing, 

 for their growth was already retarded by the addition 

 of four drops, and that with six their development w r as 

 often completely stopped, whilst the B. coli communis 

 grew in the presence of seven to eight drops of this 

 acid. Moreover this acid methyl-violet-gelatine, whilst 

 preventing the growth of the typhoid bacillus, was often 

 in Dunbar's experiments liquified by foreign organisms 

 when very polluted waters were examined. 



Holzs Method ^ Assuming that the growth of the 

 typhoid bacillus upon potatoes presents quite distinct 



1 ' Untersuchungen iiber den Nachweis der Typhusbacillen,' Zeit- 

 sclirift fur Hygiene, vol. viii., 1890, p. 143. 



