ALKAJLI-rOKMIlsrG BACTERIA FOUlsTD IN MILK. 33 



Nessler's reagent; consequently all the cultures in sodium-nitrite- 

 lactate medium were tested for the presence of ammonia. The test, 

 however, was found to be negative and since it was known that these 

 bacteria could utilize ammonia as a source of nitrogen the results 

 indicate that as the nitrite was reduced to ammonia the lattgr 

 was immediately used up. 



The results showing the reduction of nitrate and nitrite by the 

 alkali-forming group of bacteria are of particular interest, since they 

 point out the difficulty of obtaining accurate tests for these reductions 

 without a thorough understanding of the physiology of the bacteria. 



ARBITRARY GROUPING OF THE ALKALI-FORMING BACTERIA FROM MILK. 



An attempt has been made to arrange into groups the 68 alkah- 

 forming bacteria used in this study in order to show the possibihty 

 and emphasize the use of the organic-acid salts, carbohydrates, and 

 alcohols as test substances when used as the only source of carbon 

 in a synthetic medium. In the chart, figure 2, it may be seen 

 that the cultures have been divided first according to their morphology 

 into cocci and bacilli, then further subdivided on the basis of their 

 fermentation of dextrose. After the division of the cultxu-es into 

 positive and negative dextrose, they are again divided into sub- 

 groups according to their abifity to ferment mucic, tartaric, malonic, 

 or glyceric acid salt. In this grouping, in order to differentiate fur- 

 ther and bring out the main points of difference in the cultures, the 

 following organic salts were used — formic, butyric, valeric, hippuric, 

 uric, and urea. While these organic-acid salts were used to group 

 the cultures, it often happened that other easily fermented organic- 

 acid salts not mentioned had to be utilized to distinguish the different 

 subgroup members further. Examples of such are the salts of 

 mafic, acetic, and citric acids. 



For the convenience of those who may study alkafi-forming organ- 

 isms each subgroup has been given an arbitrary number. The fer- 

 mentation of dextrose and the salts of the organic-acid salts men- 

 tioned were, for the purpose of this paper, considered primary char- 

 acteristics in distinction to the secondary characteristics which are 

 shown in the lower half of figure 2. It is of interest to observe that 

 the alkaU-forming bacteria studied in this work and grouped accord- 

 ing to what are considered primary characteristics, also had secondary 

 characteristics which correlated with the primary. Thus by refer- 

 ring to the chart it may be seen that all the fluorescent cultures fell 

 into subgroup 4, aU the gelatine liquefiers feU into subgroup 6, while 

 aU the cultures that fermented the alcohols, such as mannite and 

 glycerin, feU into subgroup 9. The only cultures that showed gas 

 in dextrose broth also were in subgroup 9. The pigment formers, 

 which were also the cultures that fermented saccharose, fell into 



