The influence of different extracts on the acid production of two strains of Streptococcus cremoris and two of Betacoccus cremoris isolated from Kingston cheese has been studied.The enriching entity has no effect on acid production by Streptococci in sugar broth. Enrichment with yeast or alfalfa extract causes not only a marked increase in the acid production by Betacocci, but also a definite stimulating effect on the rate of acid production.Enriching milk with yeast or alfalfa extract has a marked stimulating effect on the vital activity of the Betacocci and of Streptococcus EMB1173, but is without influence on Streptococcus EMB1195. The response of culture EMB1173 is immediate and direct, but in the case of cultures EMB2168 and EMB2173 the action of the enriching entity is cumulative in its effect. Alfalfa extract would appear to provide, in the case of Betacoccus EMB2173, a stimulating influence not to be found in yeast extract.The influence of other forage crop enrichments on rate of acid production has also been studied. The factor or factors present in alfalfa and shown to exert a stimulating influence on the vital activity of the organisms are to be found to some extent in all forage crops investigated.