THE KINDS OF MICRO-ORGANISMS IN MILK 345 



related to our Group 1, as well as to some closely connected with 

 this type. 



"Group 4 includes the high acid-forming bacteria, of which 

 the Bacillus bulgaricus is the type. This organism is distinguish- 

 able from those of the preceding groups by its slender rod-like 

 form, its characteristic colonies on agar, its inability to grow in 

 ordinary artificial media, and its growth in the presence of free 

 acid. Bacillus bulgaricus has been studied in its relation to the 

 fermented milks extensively used in Turkey and the neighboring 

 countries. It has recently been shown that it is very widely dis- 

 tributed and may be isolated from almost any sample of mixed 

 milk. Its growth at normal temperatures is so slow that it is 

 improbable that it is a factor in the ordinary souring of milk." 



The authors state. that these groups are connected only by 

 their ability to ferment lactose to acid, and the consequent pre- 

 cipitation of the casein. They attempt a scientific classification 

 of lactic acid bacteria by grouping them according to their ability 

 to ferment raffinose and glycerin and by the liquefaction of gelatin. 



A more elaborate and comprehensive classification of lactic 

 acid bacteria has been proposed by Lohnis. This author dis- 

 tinguishes four groups of lactic acid bacteria, namely: 



1. Bacterium pneumoniae (Friedlander) : The members of this 

 group are plump rods, Gram-negative, gas formers; they grow 

 luxuriantly on laboratory media and do not liquefy gelatin. 

 Representatives are Bacillus acidi lactici (Hlippe) and other mem- 

 bers of the coli-aerogenes group. 



2. Streptococcus pyogenes (Rosenbach): This group is com- 

 posed of oval, spheric, lancet-shaped, or flat cocci, inclined to 

 chain formation and anaerobiosis; they are Gram-positive; grow 

 scantily on laboratory media, better when carbohydrates are 

 present. Representatives of this group are Streptococcus lacticus, 

 the streptococci from kefir, and other fermented milks, Bacillus 

 acidi lactici 1 and 2 of Conn and Esten, Streptococcus acidi 

 paralactici non-liquefaciens Halensis of Hashimoto, some strep- 

 tococci isolated from cheese, Bacterium lactis acidi of Leichmann, 

 and many other bacteria with the morphology and properties of 

 streptococcus. 



3. Bacterium caucasicum (Kern) : The members of this group 

 are long, more or less slender rods, inclined to filament formation 

 and anaerobiosis; they are Gram-positive in young cultures, 

 Gram-negative in old cultures; and some produce large amounts 

 of acid in milk. Some produce gas, but these are exceptions. 

 They grow poorly on laboratory media; generally coagulate milk, 

 although some do not; some have an extraordinarily high opti- 

 mum temperature. Representatives of this group are: Bacillus 



