22 STORRS AGRICULTURAL EXPERIMENT STATION. 



3. B. lactici acrogenes is also very frequenth' present, though 

 rarel}' in numbers as great as those of the first two species 

 mentioned. It produces a large, intensely acid colon}^, com- 

 monly growing ou the surface, and forming frequently a 

 thick, white bead, which occasionally develops a bubble of gas. 

 Whether these colonies can be differentiated from those of B. 

 coli comvmnis we have not yet ascertained. The two organisms 

 produce colonies very similar to each other, and while in some 

 cases we believe that we can .separate the two by the appear- 

 ance of their colonies, we are not yet sure of this differentia- 

 tion. In our tables, therefore, the column which is headed 

 "i?. aerogenes'' includes i>. acrogenes and B. coli comvnuiis, if 

 the latter is present, no attempt being made in the.se tables to 

 differentiate the two. 



4. Next to the acid bacteria the most common organism is 

 a type which produces no change in the action of the litmus, 

 but develops a small, opaque colon}- quite easil}^ recognized. 

 It produces a slightly alkaline reaction which sometimes neu- 

 tralizes the acid of neighboring lactic colonies. This organism, 

 which in the tables is called a streptococcus, is found in nearly 

 every sample of milk, and evidence given elsewhere has indi- 

 cated that it is present in the udder of the cow, so that the milk 

 ducts may be regarded as at least one of its sources. It does 

 not represent a single species of bacteria but rather a group of 

 allied forms. We have found that among the organisms tabu- 

 lated under this name their are several species, all agreeing in 

 producing no noticeable action on the litmus gelatin or in milk. 

 Some are streptococci and others are short bacilli. Since the 

 different species cannot be readily differentiated upon our plates 

 we group them of necessity under one head, designated the 

 streptococcus group. 



5. We have divided the liquefying bacteria into two groups. 

 The first, called rapid liquefiers , liquefy the gelatin very rapidly; 

 while the second, called slow liqiccjiers, require several days to 

 produce liquefaction, and even on the older plates the colonies 

 are small, never extending over the plate. A further differen- 

 tiation is doubtless possible but it has not as yet been attemped. 



6. Sarcina lutea proves to be almost uniformly present in 

 our milk. It is easily distinguished from other colonies by its 

 yellow color, which reddens the litmus around it. All yellow 

 acid calonies have proved to be this species. 



