HOUSTON'S METHOD OF WATER EXAMINATION 859 



2. The presence of the colon bacillus and of colon-like bacteria and the 



approximate numbers of these organisms. 



3. The presence of the Bacillus enteritidis sporogenes and the numbers 



in which it occurs. 



4. The presence of streptococci. 



1. The total number of organisms present is ascertained by methods similar 

 to those described above (Section II. 1.) and both agar and gelatin plates 

 may be sown to ascertain the numbers of organisms which will grow at 37 C. 

 and 22 C. respectively. 



2. The detection of the colon bacillus. For this determination Houston 

 uses MacConkey's bile-salt fluid (p. 412) as the preHminan^ enrichment 

 medium and then MacConkey's agar medium for isolation from the pre- 

 liminary medium. 



3. The presence of the Bacillus enteritidis sporogenes is determined by 

 sowing known volumes of the water in milk and cultivating anaerobically. 



4. For the detection of streptococci measured quantities of the water are 

 sown in broth and incubated at 37 C. 



Experimental data. 



1. Apparatus and media required. 



(a) Pipettes graduated to measure (1) 100 c.c. (2) 10 c;c. (3) 1 c.c. (4) O'l c.c. 

 (/3) Media. 



(1) Test tubes containing a measured 9 c.c. of sterile distilled water. 



(2) Tubes containing about 10 c.c. of sterile gelatin and others containing 



about 10 c.c. of sterile agar. 



(3) Tubes containing about 10 c.c. of MacConkey's lactose-bile-salt 



fluid 1 (p. 412). 



(4) Tubes containing a measured 10 c.c. of MacConkey's fluid of double 



strength : 



Peptone, - 40 grams. 



Lactose. - 10 



Sodium taurocholate, - 10 



Chalk, 1 .... 20 



10 per cent, litmus solution, - - - 200 c.c. 



Water, ... ... 1000 



(5) Tubes containing a measured 50 c.c. of MacConkey's fluid of triple 



strength : 



Peptone, - 60 grams. 



Lactose, - 20 



Sodium taurocholate, - 15 



Chalk, - 30 



10 per cent, litmus solution, 300 c.c. 



Water, - - 1000 



(6) Tubes containing about (i) 50 c.c. and (ii) 10 c.c. of sterilized milk 



from which the cream has not been removed. 



(7) Tubes containing about 10 c.c. of sterile broth. 



(8) Petri dishes. 



2. Technique. 



Remove the bottle containing the sample of water from its case and 

 thoroughly mix the contents by shaking. Take out the stopper and flame 

 the mouth of the bottle. 



1. Sow 100 c.c. into 50 c.c. of MacConkey's triple strength fluid. 



1 Chalk is added in order that the acid and gas produced by lactose-fermenting organisms 

 may be more readily recognized. Some observers prefer a small thin-walled glass tube 

 (Durham's tube) which is inverted into the medium and serves to collect the gas. 



