34 DAIRY BACTERIOLOGY 



cereale (Bacillus Delbrucki), they attack casein to a considerable 

 extent, and thus come to play an important part in the ripening 

 of strongly scalded cheeses such as Emmental or Gruyere. To 

 this genus belong the strongest acid producers, e.g., Tbm. helve- 

 ticum (Bacterium casei e), which may produce over 2-7 per cent, 

 of inactive lactic acid, and which plays an important part in 

 the ripening of Emmental cheese. Tbm. bulgaricum (Bacillus 

 bulgaricus) forms up to 1-7 per cent, of Isevo acid, and Tbm. 

 jugurt forms as much inactive acid as Tbm. helveticum, and grows 

 in peculiar feathery- shaped colonies. These two last-mentioned 

 organisms occur in Bulgarian sour milk. 



Organisms belonging to the Streptobacterium genus are short or 

 long chains of short or long rods, which as a rule have a maximum 



FIG. 35.Thermobacterium helveticum from FIG. 36. Streptobacterium casei from 

 Emmental Cheese. (After Freudenreich.) Danish Dairy Cheese, x 1,000. 



X 1,000. 



of 35 to 40 C. ; they gradually come to predominate in dairy 

 products which are kept at temperatures below 35 C., and are 

 therefore frequently found in cheese. They form inactive or 

 dextro acid. Sbm. casei (Bacterium casei a) hydrolyses casein, 

 while Sbm. plantarum does not do so. 



The Betabacteria almost always form inactive acid, and when 

 in a freshly isolated state, perceptible amounts of by-products ; 

 they have no action on casein, and as a rule do not grow well 

 in milk. As examples may be named Bbm. breve and longum 

 (Bacterium casei y and 8 respectively). The former ferments 

 arabinose strongly, and frequently also xylose ; it has a maximum 

 temperature of 38 C. The latter never ferments arabinose, but 

 frequently ferments xylose and raffinose ; its maximum tempera- 

 ture is 45 C. Bbm. caucasicum is the chief constituent of Kefir 



