ALKALI-FORMIlSrG BACTERIA FOUND IN MILK. 37 



' 7. Organic-acid salts were easily available as sources of carbon 

 when used in the synthetic medium^ and in most cases an alkaline 

 reaction was produced, due to the formation of bicarbonates or car- 

 bonates. The exceptions were when the salts of n-butyric, n- 

 valeric, or caproic acids were used. These acids may be split into 

 other acids and if the fermentation is not carried far enough the 

 reaction may become acid. 



An attempt was made to determine from what radical or radicals 

 the alkah-forming bacteria obtained their carbon. The results of 

 the study indicate that it may come from the methyl, alcohol, or 

 aldehyd (as in formic acid), but not from the carboxyl group (as in 

 oxalic acid) . Carbon was most easil}^ obtained from the . methyl 

 group (as in succinic, acetic, etc.), and about as well from the methyl 

 and alcohol group when attached (as in citric, malic, or lactic acid) . 

 Carbon was not easily available from the alcohol radical when it was 

 linked to a carboxyl and another alcohol radical (as in mucic, tar- 

 taric, and glyceric acids). It was not available from an alcohol 

 radical when linked to a carboxyl (as in glycolic acid) . Apparently 

 the benzol ring can be split by some bacteria, for a few of the cul- 

 tures were able to obtain their carbon from the salts of benzoic and 

 salicylic acids. 



Some of the cultures were able to obtain both nitrogen and carbon 

 from urea and also from uric and hippiu-ic acids. Numerous known 

 cultures, some of which give the characteristic alkaline milk reaction 

 of the alkali-forming group, were capable of utilizing the salts of 

 organic acids as a source of carbon when grown in a synthetic 

 medium. Among these were cultures of proteus, typhoid, paraty- 

 phoid, and dysentery; also B. abortus, B. hronchisej^ticus, B.fxcalis 

 alkaligenes, and B. enteriditis. It is believed therefore that the 

 salts of organic acids may serve as valuable carbon-containing test 

 substances for the further identification of bacteria. 



8. The alkali-forming bacteria readily used the nitrates and 

 nitrites as sources of nitrogen, but when tested for the reduction of 

 nitrates and nitrites in the commonly used peptone medium very 

 few showed any evidence of reduction. The ordinary method of 

 testing the reduction of nitrates to nitrites is of no value when 

 alkali-forming bacteria are being studied. This may be equally true 

 of other groups of bacteria. Special media should be used, there- 

 fore, whenever possible. 



9. An arbitrary division of the alkali-forming bacteria found in 

 milk has been made. This classification was based primarily on the 

 fermentation of dextrose and the salts of organic acids, and serves 

 to show the value of the fermentation of the organic-acid salts for 

 this purpose. Each subgroup has been given a number as a matter 

 of convenience for those who may study these types of bacteria in 



