Definition of the alkali-forming groups of bacteria 2 Cause of the alkaline reaction in milk 3 Sources of the alkali-forming bacteria 9 Morphology and growth 10 Sources of nitrogen 11 Fermentation of carbohydrates 12 Fermentation of alcohcls 17 Fermentation of salts of organic acids 19 Reduction of nitrates and nitrites 30 Arbitrary grouping of the alkali-forming bacteria from milk 33 Summary and conclusions 35 HISTORICAL REVIEW. Occasionally references to the alkali-forming bacteria are found in bacteriological literature. This group of bacteria has not received much attention, probably because under the ordinary conditions of plating their presence can not be detected, and as a consequence their* rather wide distribution has been overlooked. The fact that alkali-forming bacteria are often present in market milk in large numbers was first brought to the attention of the authors during some studies (1) 1 on the bacteriology of raw and pasteurized milk. At that time no suitable means were available for obtaining any exact figures on their numbers in market milk, so they were classed with the inert types of bacteria. Wolff (12) in a study of bacteria which developed in milk found nonliquefying short rods, colonies of which resembled those of the colon-aerogenes group. These organisms were strict aerobes which produced neither acid nor gas but turned milk alkaline without any other change. Shippen (10) also found organisms, in the milk supply of Baltimore, which gave an alkaline reaction in milk without peptonizing or coagulating it. He found that these organisms in cultural reactions closely resembled i The numbers in parentheses refer to " Literature cited " at end of bulletin. 104410°-19-Bull. 782 1 100 c. c. of milk. Citric acid in 100 c. c. of milk.

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