320 THE CLASSIFICATION OF BACTERIA 



characteristic granules. No spores. Motility slight or absent. Gram-positive. Shght 

 fermentative activities. Microaerophilic. Usually jiarasitic. 

 Type species. Erysi'pe.lothrix rhusiopathice. 



Mycobacterium. — Slender rods which are stained with difficulty but which, when once 

 stained, are acid-fast. Cells are sometimes swollen, clavate, cuneate, or even branched. 

 Non-motile. Gram-positive. No endospores. Growth on media slow. Aerobic. 

 Several species are pathogenic to animals. 



Type species. Mycobacterium tuberculosis. 



Corynebacterium. — Gram-positive rod-hke forms, arranged usually in a palisade. Not 

 acid-fast. Often with club-shaped swellings at the poles, generally with irregularly staining 

 segments or granules. Non-motile, non-sporing. Growing aerobically or under micro- 

 aerophihc conditions, but often capable of anaerobic cultivation. Never forming gas in 

 carbohydrate media, in which they may or may not produce acidity. They may or may 

 not hquefy gelatin or serum. Some species produce a powerful exotoxin. 



Type species. Corynebacterium diphthericB. 



Fusiformis. — ObUgate parasites. Anaerobic or microaerophihc. Cells frequently 

 elongate and fusiform, staining somewhat unevenly. Filaments sometimes formed. 

 Non-branching ; sometimes highly pleomoriiliic. Non-motile. No spores. Reaction to 

 Gram's stain variable, but mainly Gram-negative. Growth in laboratory media feeble. 



Type species. Fusiformis termitidis. 



Pfeifferella. — Small, slender, usually non-motile, Gram-negative rods, often staining 

 irregularly, and sometimes forming threads or showing a tendency towards branching. 

 Growth on all media is rather slow ; gelatin may be slowly liquefied ; fermentation of 

 carbohydrates is very weak ; characteristic brown honey-hke growth on potato. 



Type species. Pfeifferella mallei. 



Hydrogenomonas. — Monotrichate short rods capable of growing in the absence of 

 organic matter, and securing growth energy by the oxidation of hydrogen (forming 

 water). 



Type species. Hydrogenomonas pantotropha. 



Methanomonas. — Monotrichate short rods capable of growing in the absence of organic 

 matter and securing growth energy by the oxidation of methane (forming carbon dioxide 

 and water). 



Type species. Methanomonas methanica. 



Carboxydomonas. — Rod-shaped cells capable of securing growth energy by the oxida- 

 tion of carbon monoxide (forming carbon dioxide). 

 Type species. Carboxydomonas oligocarbophila. 



Acetobacter. — Cells rod-shaped, frequently in chains, non-motile. Cells grow usually 

 on the surface of alcoholic solutions as obligate aerobes, securing growth energy by the 

 oxidation of alcohol to acetic acid. Also capable of utihzing certain other carbonaceous 

 compounds, as sugar and acetic acid. Elongated, filamentous, club-shaped, swollen and 

 even branched cells may occur as involution forms. 



Type species. Acetobacter aceti. 



Nitrosomonas. — Cells rod-shaped or spherical ; motile or non-motile ; motile forms 

 possess polar flagella. Capable of securing growth energy by the oxidation of ammonia 

 to nitrites. Growth on media containing organic substances scanty or absent. 



Type species. Nitrosomonas europcea. 



Nitrobacter. — Cells rod-shaped, non-motile, not growing readily on organic media or 

 in the presence of ammonia. Cells capable of securing growth energy by the oxidation 

 of nitrites to nitrates. 



Type species. Nitrobacter winogradskyi. 



