BILE SALT BROTH 157 
In the case of crude sewage, effluents, or river water, definite dilutions of the 
cubic centimetre are made in each instance, viz., — 1 '— — — , according as it is 
desired to determine whether there are 10, 100, 1,000, 10,000, 100,000 B. coli 
present in the cubic centimetre of the sample (other dilutions can also be made as 
occasion demands). Four distinct dilutions are severally tested, and three 
determinations made of each dilution. Thus, twelve tubes of the medium are used 
for each sample. The tubes are incubated at 42 0 C. for forty-eight hours, as in the 
previous instance. 
It is found in practice that in the large majority of cases the characteristic 
reaction is obtained within twenty-four hours, frequently within eighteen hours. 
In the case of the higher dilutions more time seems to be requisite, so that it is 
advisable to incubate for forty-eight hours. It the reaction has not occurred within 
that time, it can be definitely stated that further incubation will not produce it. The 
medium may become acid or slowly decolourized, but the formation ot gas is never 
observed ; when it occurs, it takes place rapidly. 
Resu 
LTS 
A. Drinking water — 
1. Moorland filtered water: 
Samples . . . . . 118 
Number of reactions ... 5 
„ „ due to B.C.C. . 5 
2. River filtered water : 
Samples . . . . . 169 
Number of reactions . . . 16 
„ ,, due to B.C.C. . 1 6 
B. River water: 
Samples . . . . . 41 
Number of reactions . . . 41 
„ ,, due to B.C.C. . 41 
C. Milk: 
Samples . . . . . 103 
Number of reactions ... 98 
,, ,, due to B.C.C. . 98 
D. Sewage and sewage effluents: 
The reaction has always been obtained in every sample examined. 
