BACTERIA 33 



(A) No catalase formation, nitrate reduction nor surface growth. 



(a) Forming only traces of by-products in addition to lactic, acid. 



Rod forms . . Genera Thermobacterium and Strepto- 



bacterium. 

 Sphere forms . . Genus Streptococcus. 



(b) Generally forming appreciable amounts of gas and other by- 



products in addition to lactic acid. 



Rod forms . . Betabacterium. 

 Sphere forms . . Betacoccus. 



(B) Usually forming catalase, reducing nitrates and showing 

 surface growth. 



Rod forms . . Microbacterium. 

 Sphere forms . . Tetracoccus 1 . 



Group B has been included because it forms a limiting group to 

 the lactic acid bacteria on the one side, just as the Coli and 

 Aerogenes group do on the other, though none of these can be 

 reckoned as true lactic acid bacteria. The last-mentioned group 

 includes group A, and also Bacterium bifidum, which, on account 

 of its branched form and obligate anaerobic character, occupies a 

 unique position. 



Group A. Although we may well suppose that the genera 

 Streptobacterium and Streptococcus and the genera Betabacterium 

 and Betacoccus are respectively more closely related to one another 

 than the various rod forms to one another, and the various sphere 

 forms to one another, we will, however, seeing that the rod forms 

 as a whole are stronger acid producers than the sphere forms, keep 

 up the old tradition and treat the rod and sphere forms separately. 



(1) Rod Forms (named Lactobacilli by Beijerinck). Short or long, 

 straight or curved rods which may grow out into long threads. 

 Sometimes they contain granules which stain more readily with 

 methylene blue than the rest of the protoplasm. They may 

 occur in pairs or chains of varying lengths and regularity of form. 

 To this group belong the most typical of the lactic acid bacteria, 

 which produce, and are able to stand, greater quantities of lactic 

 acid than the other lactic acid organisms. Some of them may 

 form as much as 3 per cent, of lactic acid in milk. The members 

 of the Thermobacterium genus are long rods, which thrive at 40 to 

 50 C. or even higher temperatures, but not below 22 C. ; they 

 will generally obtain predominance in milk kept above 40 C. They 

 form Isevo or inactive lactic acid, and with one exception, Tbm. 



1 Common term for acid-forming Micrococci and Sarcmae. 



D.B. 3 



