ALKALI-FORMING BACTERIA FOUND IN MILK. 35 



subgroup 11. Another noticeable secondary characteristic was the 

 uniform limiting Ph value in dextrose medium A, the composition 

 of which was given on page 13. Each subgroup of the dextrose 

 fermenters utilized the carbohydrate to a practically constant limit- 

 ing hydrogen-ion concentration, as is shown for example in subgroup 

 10, where all the 6 cultures fermented dextrose to Pg 6.2 after 7 

 days' incubation at 30° C. The reaction in milk was similar in sub- 

 groups 4, 5, and 6. In these 3 groups there was first a primary alkali 

 fermentation which was followed by what was apparently a second- 

 ary acid fermentation, during a period of 30 days' incubation. The 

 secondary characteristics of this group have been given in detail so 

 as to emphasize further and show the possibility of the new method of 

 grouping alkali-forming bacteria according to their ability to utilize 

 carbon when supplied in a synthetic medium from organic-acid salts, 

 carbohydrates, and alcohols. It was impossible to make this study- 

 cover all types of the alkali-forming bacteria, because the definition 

 chosen for this group is so simple and yet so comprehensive that it 

 must include a very large number of species of bacteria. Therefore, 

 the scheme for grouping this particular collection of alkali-forming 

 organism is not intended for a definite classification of aU the alkali- 

 forming group of bacteria. It should serve, however, as a possible 

 basis for future work along this line and particularly to draw attention 

 to the fact that the fermentation of organic-acid salts is a reliable and 

 important means for classification, especially for organisms of this 

 type occurring in soil. 



SUMMARY AND CONCLUSIONS. 



1. The alkali-forming bacteria may be defined as those bacteria 

 which produced an alkahne reaction in milk without visible signs of 

 peptonization. In htmus milk this reaction appeared sometimes 

 within 48 hours, usually within 5 days, while occasionally a longer 

 period was required. The alkaline reactions were caused primarily 

 by the oxidation of the salts of citric acid to alkaline carbonates. 

 Other organic-acid salts if present in milk may also be similarly 

 fermented. Ammonia played little or no part in causing the alkaline 

 reaction during the first 7 days of incubation, but at later periods 

 a few cultures produced considerable ammonia. Several cultures 

 showed a primary alkaline fermentation which was followed by what 

 was probably a secondary acid fermentation. 



2. The alkah-forming bacteria studied were isolated principally 

 from milk, a few being obtained from ice cream. These organisms 

 were found in large numbers in numerous samples of soil and also 

 water. They were present in large numbers on the hands of farm 

 laborers, and in unsterihzed milk utensils. While not present in 

 the udders of cows, the alkali-forming bacteria were present in 

 relatively small numbers in cow feces. It seems evident that the 



