76 MAUD MASON OBST 



ox-bile requires one-half day each week of the time of the helper 

 and fifty cents for three gallons for its collection, thereby cost- 

 ing approximately ten cents per liter of medium. Lactose 

 broth can be made as desired from ingredients which do not 

 materially change during storage. 



In the experiments here reported check analyses were made 

 upon a series of samples of water, using lactose peptone ox-bile 

 and lactose broth. The bile was never used later than a week 

 after collection. It was sterilized upon receipt and stored during 

 this period at a temperature of 1°C. It was enriched with 1 per 

 cent lactose and 1 per cent peptone, and tubed m Dunham 

 tubes. The lactose bouillon was made from neutral nutrient 

 broth prepared with 0.5 per cent Liebig's meat extract, 1 

 per cent peptone and 1 per cent lactose. This medium was 

 compared with lactose peptone ox-bile in the examination of 191 

 samples of water with the following results: 



No gas-producing organisms in 10 cc. quantities in either lactose 

 or bile in 68 samples. 



Gas-producing organisms in the same dilutions in lactose and in 

 bile in 59 samples. 



Gas-producing organisms in higher dilutions in bile than in lactose 

 in 3 samples. 



Gas-producing organisms in higher dilutions in lactose than in bile 

 in 61 samples. 



Lactose showed gas-producing organisms in one-half as much water 

 as were shown by bile in 12 samples. 



Lactose showed gas-producing organisms in one-fifth as much water 

 as were shown by bile in 12 samples. 



Lactose showed gas-producing organisms in one-tenth as much water 

 as were shown by bile in 19 samples. 



Lactose showed gas-producing organisms in one-hundredth as much 

 water as were shown by bile in 5 samples. 



From every sample B. coli was isolated from the highest 

 dilution tube showing gas. This shows the ratio of inhibition 

 of bile on B. coli when compared with lactose bouillon to be 

 about 2:1. 



