EXAMINATION OF WATER 585 



of liquefaction. If atypical Bacilli coli (see pp. 388 and 

 389) are met with, the fact should be noted, but their 

 significance is not yet fully determined. 



STREPTOCOCCI. It is a distinct advantage to search 

 for streptococci. They may be looked for by making 

 hanging- drop preparations of the fluid media employed for 

 the preliminary cultivation of the B. coli (glucose or lactose 

 bile-salt peptone water, etc.) The presence or absence of 

 streptococci in these tubes gives also a quantitative value 

 to the examination, just as in the case of B. coli, and the 

 result obtained should be stated. The streptococci can 

 be readily isolated on Conradi-agar plates. 



According to Houston (loc. cit.), faeces contain at least 100,000 

 streptococci per gramme. The type of streptococcus generally present 

 is one forming short chains, producing a uniform turbidity in 

 broth, acid and clot in litmus milk within five days at 37 C., and 

 non-pathogenic for mice. (See Table, p. 235.) 



BACILLUS WELCHII. As already stated, it is not essential 

 as a routine procedure to search for the Bacillus Welchii 

 (enteritidis sporogenes), though in certain instances it may 

 be of advantage to do so. A negative result in such 

 cases is probably of more value than a positive one. 



For the isolation of B. Welchii, 500 c.c. of the water may be 

 filtered through a Pasteur-Chamberland filter, the deposit is sus- 

 pended in 5 to 6 c.c. of sterile water, and 1 c.c. of the suspension 

 added to each of five to six tubes of sterile milk, which are then 

 heated to 80 C. for ten minutes in a water-bath, and incubated 

 anaerobically at 37C. for forty-eight hours (filter-brushing method). 

 A better method * is to employ large boiling tubes or small Erlen- 

 meyer flasks, each containing 25 to 50 c.c. of sterile milk. To each 

 tube a quantity of water equal to that of the milk is added, the 

 tubes are then heated in a water-bath to 80 C. for fifteen to twenty 

 minutes, some sterilised oil or melted vaseline is poured on the 

 surface to exclude air, the tubes are cooled in water to 37 C. or 

 thereabouts, and incubated for forty-eight hours at 37 C. Not 

 less than 200 c.c. of the water should be used. The typical change 



1 R. T. Hewlett, Trans. Path. Soc. Lond., vol. Iv, 1904, p. 123 



