716 A MANUAL OF BACTERIOLOGY 



13. coli, the colour changing to a canary yellow, accompanied by 

 a green fluorescence. The B. enteritidis (Gartner) also reduces 

 neutral-red, but the B. typhosus does not do so, nor do strepto- 

 cocci, B. pyocyaneus, and Vibrio cholerce. Some anaerobes also 

 possess a reducing action. Glucose agar or broth (0-5 per cent, 

 of glucose) is employed, and to every 10 c.c. of the medium 

 0-1 c.c. of a 0-5 per cent, aqueous solution of neutral-red is added. 

 Savage recommends the following procedure : 10 c.c. of the 

 water are added to a 10 c.c. tube of neutral-red broth ; also 

 to 40 c.c. of the water contained in a bottle or flask a 10 c.c. 

 tube of the broth of quadruple strength is added. Both are 

 incubated at 37 C., and examined daily up to eight days. If 

 reduction occurs, B. coli is almost certainly present in the 

 water ; if reduction does not occur its presence is highly 

 improbable. 



(4) Glucose formate broth (Pakes). To ordinary meat infusion 

 1 per cent, peptone, 0-5 per cent, sodium chloride, 2 per cent, 

 glucose, and 0-4 per cent, sodium formate are added. When 

 these have been dissolved by heating, the medium is neutralised 

 (indicator, litmus), and after neutralisation 2 c.c. of normal caustic 

 soda solution per litre are added ; the broth is then steamed for 

 twenty minutes, filtered, and distributed into test-tubes, 10 c.c. 

 in each, which are steamed for twenty minutes on each of three 

 successive days. These tubes are inoculated with the water, and 

 incubated anaerobically at 42 C. for twenty-four to seventy-two 

 hours. Tubes showing any growth at the end of twenty-four, 

 forty-eight, or seventy-two hours are removed and examined 

 microscopically and by plating. 



(5) Bile-salt lactose agar (MacConkey). This medium is pre- 

 pared by adding to 1,000 c.c. of tap-water in a flask 2 per cent, 

 of peptone, 0-5 per cent, of sodium taurocholate, and 1-5 per cent, 

 of agar. The mixture is autoclaved at 105 to 110 C. for one and 

 a half hours, cleared with a small addition of white of egg, and 

 filtered. To the filtrate 1 per cent, of lactose is added. The 

 medium is then distributed into test-tubes, 10 c.c. in each, and 

 sterilised by fifteen minutes' steaming on three successive days. 

 Plates are made and incubated at 37 -40 C. for forty-eight hours. 

 XJJ4J colonies of organisms which ferment lactose with the forma- 

 tion d'f^acid are surrounded with a cloudiness or haze owing to the 

 precipitation of frjio taurocholate. 





