DETECTION OF PATHOGENIC BACTERIA IN WATER 285 



searching for pathogenic organisms special methodf^ 

 must be devised and adopted according to the nature 

 of the particular microbe of which we are in quest, and 

 that only under the most exceptional circumstances is 

 there any possibility of such pathogenic bacteria being 

 found in the course of ordinary plate cultivations made 

 with natural waters, the colonies of the common water- 

 bacteria almost invariably so predominating as to 

 exclude all others present only in small numbers. Such 

 special methods have, as pointed out above, already 

 been employed, more especially for typhoid and cholera 

 bacilli, as well as for anthrax spores ; in all cases these 

 methods should be so arranged as to permit of the 

 examination of larger volumes of water, as in this 

 manner the chance of discovery is correspondingly 

 increased. 



Note. — In examining water for the typhoid bacillus it is advisable to 

 pass a considerable volume, 250 c.c. or upwards, through a sterile porce- 

 lain or infusorial earth filter (see p. 172), and then to transfer the deposit 

 on the surface of the cylinder by means of a sterile brush into a small 

 quantity of sterile water ; the latter, which then contains the bacteria h-om 

 the large original volume of water, should be treated by phenol-broth 

 culture or one of the other methods of typhoid detection. To assist the 

 diagnosis of the typhoid bacillus in the presence of the B. coH commmiis, 

 Schild (Zeitsclirift f. Hygiene^ vol. xvi. 1894, p. 373) recommends the 

 use of broth to which ^ formalin^ hsis been added. Formalin maybe 

 procured from Schering, in Berlin, and consists of a concentrated 

 (40 per cent.) aqueous solution of formaldehyde. It should be added by 

 means of a sterile pipette to ordinary neutral broth, of course after the 

 sterilisation of the latter, as heating volatihzes the formaldehyde. The 

 proportion recommended by Schild is 1 : 7000, and he states that, whereas 

 the B. coli communis will flourish in this formalin -broth, rendering it 

 turbid in from 8-24 hours, the typhoid bacillus refuses to grow and the 

 liquid remains clear. This formalin-broth must only be used when 

 freshly prepared, as the formaldehyde volatilizes on being kept. Schild 

 states that in adding the formahn to the sterile broth he has only rarely 

 been troubled with contaminations, and then they were traced to moulds 

 which were easily recognisable. 



