Apr.a2. i9i8 Streptococci Concerned in Cheese Ripening 239 



against classifying it with the i-od forms, as the generic name " Bacterium" 

 implies. Undoubtedly some authors have included under the name 

 "Streptococcus lacticus" the varieties of streptococci which the results 

 of this study show to be quite distinct. 



S. lacticus has a tendency to form elongated cells with pointed ends, 

 and to separate in pairs rather than remain together in long chains. 

 These characters are variable, however, according to the conditions under 

 which the organism is grown. The other cheese streptococci also form 

 elongated ceils under certain conditions, and some strains of them are 

 no more inclined to form chains than is S. lacticus; hence, morphology 

 will not distinguish 5. lacticus. 



A summarized description of the 5. lacticus group is given in Table I, 

 The cultures included in the table were isolated from various sources. 

 Culture 96mz was isolated from a commercial starter. Culture 96ga 

 was from an experimental Roquefort cheese, and is probably the same 

 strain as culture 96mz, the starter culture. Culture 2ak was from unpas- 

 teurized milk. Cultures 96hr and 96hs were from cream from two dairies. 

 Cultures 2am, 2al, 2ao, 2an, and 2ap were from pasteurized milk from 

 five dairies. Culture 2ab was from Cheddar cheese. Culture 96ht was 

 from soybean cheese imported from China. 



The growth of S. lacticus in litmus milk is characteristic. This strep- 

 tococcus begins to reduce the litmus before the reddening appears, and 

 before the milk coagulates, the reduction is complete beneath the pink 

 surface layer. Esten (5) noted this reaction. Sherman and Albus (19) 

 have recently confirmed it as a typical reaction for S. lacticus, although 

 other types of bacteria also give the same reaction. The data to be 

 presented in this paper show that the characteristic reduction of litmus, 

 which is correlated with other physiological activities, serves well in 

 loutine work for a differentiation of it from other varieties of cheese 

 streptococci. In an active culture of 5. lacticus curdling takes place in 

 less than 24 hours. Weakened strains require a longer time, or they may 

 fail to curdle the milk. 



Another characteristic of 5. lacticus in milk cultures is the formation 

 of crystals.* White specks or crystals are familiar in well-ripened 

 Cheddar cheese, and occur also in well-ripened Roquefort cheese. Dox 

 (2) identified the crystals from Roquefort cheese as tyrosin. Crystals 

 isolated from Cheddar cheese and from pure-milk cultures of streptococci 

 have been identified as calcium compound of an amino acid. Crystals 

 were formed by all but i of the 1 2 strains of 5. lacticus which served for 

 this study. 



In one of tne earliest descriptions of 5. lacticus, or "Bacterium lactis 

 acidi," as he called it, I^ichmann (rj) reported that it produced lactic 

 acid with no volatile acid. Jensen {12) and others have since shown 



1 For the determination of crystal formatioa milk oiltures are covered tightly with tin foil over the cotton 

 plug and incubated for six weeks or longer. 



