294 



BIOLOGICAL AND SANITARY MATTERS. 



however, usually serve. Many of the colonies on the gelatine 

 will be found to have liquefied the medium, and, if the counting 

 is delayed, the liquid may run down and contaminate the other 

 portions. The author has found that if the colonies are counted 

 in two and a-half days, no practical inconvenience is found from 

 this source. 



The Search for Bacillus Coli Communis. — Add 100 c.c. 

 of water to one of the tubes containing triple strength M'Conkey 

 medium, 10 c.c. to one of the tubes containing double strength 

 medium, and 1 c.c. of the diluted water to tubes containing- 

 the ordinary medium; mix well by shaking, and incubate 

 (Pig. 38) at 40° C. (104° F.). Examine after one and two days. 

 If acid and gas are not produced B. coli communis is absent ; 

 if acid and gas are produced there is presumptive evidence of 

 this organism. 



Dip a sterile iron wire slightly bent at one end, into each of the 

 tubes showing acid and gas, and plunge the wire into a peptone 

 water tube, stirring well. Rub the wire 

 over the surface of M'Conkey agar, and 

 incubate for twenty-four hours at 40° C'. 

 If red colonies are formed the evidence 

 for presence of B. coli communis is strong. 

 Inoculate five of the red colonies into 

 peptone water tubes, and into tubes of 

 the three sugar media. Place the sugar 

 media in the incubator at 40° C. for three 

 hours, and then for half an hour in an ice 

 chest, and incubate at 22° C. (72° F.) for 

 twenty-four hours. Incubate the peptone 

 water tubes at 40° C. for twenty-four or, 

 better, forty-eight hours. 



B. coli communis produces indole in peptone water, and ferments 

 both glucose and lactose with the formation of gas bubbles and 

 acid, but does not ferment cane sugar : a variety of this organism, 

 however, ferments cane sugar. 



Test jar Indole. — To the peptone water add a few drops of an 

 alcoholic solution of 2^-dimethyl amino-beuz-aldehyde, and a 

 few drops of a saturated solution of potassium persulphate : 

 warm slightly, and in the presence of indole a cherry-red colour 

 is produced. 



The Search for Bacillus Sporogenes Enteritidis. — Add 

 a little alum to 500 c.c. of the water, and if a turbidity is 

 not produced a fe^v drops of ammonia ; let the precipitate settle. 

 and pour off the clear solution as completely as possible, and 

 collect the precipitate by centrifuging. Add this to a tube of 

 milk, pour a layei- of melted vaseline on the surface, and heat to 



Fig, ,38. 

 Bacteiioloeical Incubator. 



