QUALITATIVE BACTERIOLOGICAL ANALYSIS. 101 



to the influence of the slightly alkaline media, and to the fact 

 that better development is always obtained in fluid than in 

 solid media. The State Board of Health points out that " the 

 accuracy of these tests depends largely on attention to details, 

 time of growth, temperature, reaction, and composition of 

 media. B. coli will develop well at a temperature of 38 to 

 40 C. in from eight to twelve hours. The thermal death point 

 of most species of water-bacteria lies below that temperature, 

 and some species, which would grow, require more time, usually 

 thirty-six to forty-eight hours, for development."" According 

 to the Board the cultural characteristics of the Colon bacillus 

 are as follows : 



Agar. On the surface of glycerine-agar it produces a 

 luxuriant, smooth, moist, white growth, which is never stringy 

 to the needle. 



Gelatine. It grows well in nutrient gelatine, without lique- 

 fying that medium. 



Lactose-litmus-agar. In neutral agar, containing milk- 

 sugar and blue litmus, it grows rapidly, producing acid and 

 turning the litmus red around the colonies. 



Milk. Grown in milk, acid is produced and the milk is quickly 

 coagulated. 



Smittis Solution. In bouillon containing glucose fermentation 

 at once takes place; when the medium is placed in a bent tube with 

 one arm closed the gas is collected in the closed arm of the tube. 



Nitrate Solution. In nutrient solution, containing small 

 amounts of potassium nitrate, the nitrate is quickly and com- 

 pletely reduced to nitrite. 



Indol. In solutions containing small amounts of peptone 

 and salt, or in bouillon free from carbo-hydrates and containing 

 peptone arid salt, indol is produced. " A culture which gives 

 characteristic reactions with all of the above media belongs to 

 the Colon group undoubtedly.''' 1 



(5) Eisner and Holz recommended a medium consisting of 

 faintly acid potato gelatine for the differentiation of B. coli and 

 B. typhosus, and stated that water-bacteria did not grow well 

 on it. Further experience of this medium soon showed that 

 other bacteria were able to develop almost as luxuriantly as B. 

 coli. Kenny's modification of the potato medium has a constant 



