272 MICRO-ORGANISMS IN WATER 



features from those exhibited by other organisms, Holz 

 prepared a culture material from potatoes, which, whilst 

 resembling in all important features the conditions 

 afforded by the potato, had the advantage of being 

 transparent. (A description of the mode of preparing 

 this culture medium will be found on p. 22.) To 

 effect the destruction of other organisms Holz added 

 O'Oo per cent, of carbolic acid. But as in the case of 

 Uffelmann's medium, so with this, the B. coli com- 

 munis is not eliminated, and remains side by side 

 with the typhoid bacillus, and cannot be distinguished 

 from it. 



Pariettis Method. 1 This method consists in adding 

 carbolic acid and hydrochloric acid in certain propor- 

 tions to neutral bouillon, in the hope of thus eliminating 

 other organisms without destroying the typhoid bacillus; 

 but inasmuch as the B. coli communis is able to with- 

 stand larger doses of both carbolic acid and hydrochloric 

 acid than the typhoid bacillus, this method cannot be 

 relied upon any more than those previously described. 

 As this method, however, is very convenient for sifting 

 out the typhoid and coli from a large number of other 

 organisms, it is given in detail. 



A series of test tubes containing 10 c.c. of neutral 

 bouillon receive from 3-6-9 drops (30 drops =1 c.c.) 

 of the following solution : 



5 g. Carbolic acid 

 4 g. Pure hydrochloric acid 

 100 g. Distilled water 



These tubes are then placed in the incubator and kept 

 at 37 C. for twenty-four hours, in order to destroy any 

 organisms which may have gained access during the 

 addition of the solution. To the sterile tubes 1 to 10 



1 ' Metodo di ricerca del Bacillo del tifo nelle acque potabili,' Eivista 

 d* Igiene e Sanita publica, 1890. 



