ANAEROBIC BUTYRIC-ACID FORMERS 475 



Type 3. Micrococcus butyri aromafaciens. 



Type 4- Micrococcus candicans Fliigge. 



Type 5. Micrococcus lactis viscosi Gruber (causing slimy or ropy 

 milk). 



Type 6. Micrococcus coronatus Fliigge. 



Type 7. Micrococcus cirrhiformis Migula (forms gas). 



The Coli Aerogenes Bacteria. Under the preceding four collective 

 groups of lactic-acid bacteria proper a number of microorganisms 

 have been mentioned. Those named, however, are only a small 

 fraction of the bacteria of the groups which now comprise several 

 hundred, though it is very probable that many which in fact are 

 identical species have been described by different observers under 

 different names. Besides these lactic-acid bacteria par excellence, 

 others, such as the Bacillus coli communis and the Bacillus lactis 

 aerogenes of Escherich, form lactic acid from sugar of milk. The 

 Bacillus coli communis has been fully described in a previous chapter 

 as evidently including a number of varieties. 



The Bacillus aerogenes or the Bacterium lactis aerogenes of 

 Escherich is generally plumper and shorter than the Bacillus coli 

 communis. It is 1 to 2 micra long and 0.5 to 1 micron wide; it 

 presents itself singly, in pairs, rarely in chains, or pseudofilaments. 

 It is not motile, does not form spores, and possesses no flagella. On 

 gelatin it forms large, white, not transparent colonies. It splits 

 glucose with the formation of gas. It also ferments lactose in milk, 

 but forms from it more acetic than lactic acid. It also forms succinic 

 acid. Such lactic-acid bacteria proper as the Streptococcus Guentheri 

 and Streptococcus lacticus in their growth in milk largely prevent the 

 development of the bacteria of the coli aerogenes group. 



ANAEROBIC BUTYRIC-ACID FORMERS. 



Anaerobic bacteria which, in addition to lactic acid, also form 

 butyric acid from lactose are frequently found in milk. The first 

 bacterium of this group was discovered by Pasteur, who also recog- 

 nized its anaerobic nature. Prazmowski first introduced the name of 

 Clostridium butyricum for a bacterium of this group ; later a number, 

 several of which were evidently identical, were described under various 

 names. Beyerinck united the butyric-acid bacteria into a family 

 under the name of granulobacter, or amylobacter, because these 

 organisms when growing in a medium containing starch form char- 

 acteristic granules in their interior. A number of very important 

 anaerobic pathogenic bacteria belong to this family, such as the 

 bacillus of black leg, the bacillus of malignant edema, and others 

 described in previous chapters. 



Schattenfroh and Grassberger have classified the butyric-acid 

 formers into four groups, as follows : 



