ALKALI-FOE MING 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 alkali-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 easily 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 gly colic 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 hippuric 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. broncfiisepticus, B.fsecalis 
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 
