BACTERIAL GENERA 323 



are Voges-Proskauer negative, and fail to grow in Koser's citrate. Facultative anaerobes. 

 Some species are antigenically related. One species produces a toxin. Most species are 

 pathogenic to man, giving rise to d^^sentery or sometimes acute gastro-enteritis. Found, 

 as a rule, in the intestinal tract of human dysentery patients and contacts. 

 Type species. Shigella shigce. 



Salmonella. — Gram -negative, non-sporing rods, usually 1-3 /< long by 0-5-0-7 /i broad. 

 Primarily intestinal parasites, widely distributed in man, mammals and birds. With 

 few exceptions all species are motile, by peritrichate flagella. Easily cultivable on ordinary 

 media. Aerobic and facultatively anaerobic. Apart from a few species that form acid 

 only, acid and gas are produced from glucose, mannitol, dulcitol, and sorbitol. Lactose, 

 sucrose, and adonitol, and, except rarely, salicin are not fermented. Indole and acetyl- 

 methylcarbinol are not formed. Gelatin is seldom liquefied. HjS production is usual. 

 The species are closely related to each other by somatic and flagellar antigens ; most 

 species are diphasic. Pathogenic for man, animals, birds, or all three, giving rise to food- 

 poisoning, enteritis, or typhoid-like infections. 



Lactobacillus. — Rods, often long and slender. Gram-positive ; non-motile ; without 

 endospores. Usually produce acid from carbohydrates, as a rule lactic. Some species 

 grow best at 40° to 44° C, and some species are microaerophihc. Surface growth on media 

 poor. 



Type species. Lactobacillus caucasicus. 



Pasteurella. — Small, Gram-negative, ovoid baciUi, showing bipolar staining. Aerobic 

 and facultatively anaerobic. Powers of carbohydrate fermentation relatively slight ; no 

 gas produced. Gelatin not liquefied. Parasites in man and animals, producing charac- 

 teristic infections. 



Type species. Pasteurella aviseptica. 



Haemophilus. — Minute rods, sometimes almost coccal, sometimes thread-like ; may 

 be highly pleomorphic. Non-motile ; non-sporing ; Gram-negative ; not acid-fast. 

 Dependent for their growth on the presence of some factor, which is supphed by blood 

 pigments, and by certain plant tissues. Some species require for their growth a second 

 factor, which is present in blood, in most plant tissues, in yeast, or in the cells of other 

 bacterial species. All known species appear to be obligatory parasites ; some are patlio- 

 genie. 



Type species. Hcemophilus influenzce. 



Brucella. — Small, non-sporing, Gram-negative cocco-bacilli. Non-motile. Grow rather 

 poorly on ordinary media or may require special media. Aerobic ; no growth under 

 strict anaerobic conditions. Growth often improved by CO 2. Little or no fermentative 

 action on carbohydrates. Usually tend to produce alkaU in litmus milk, and a brown 

 pigmentation on potato. Strict parasites, occurring in man and animals, and producing 

 characteristic infections. 



Type species. Brucella melitensis. 



Bacillus. — Aerobic, spore-bearing rods, usually Gram-positive. Often occur in long 

 threads, and form rhizoid colonies. Form of rod not greatly changed at sporulation. 

 Liquefy gelatin. Mostly saprophytes. 



Type species. Bacillus suhiilis. 



Clostridium. — Anaerobic or microaerophihc rods, producing endospores, which are 

 usually wider than the vegetative organisms in which they arise — so-called Clostridium 

 forms. Generally Gram-positive. In young cultures often decompose protein media 

 through the agency of enzymes, and often ferment carbohydrates. Many species are 

 pathogenic. 



Type species. Clostridium butyricum. 



