CLASSIFICATION OP THE BACTERIA 39 



species are not infrequent in the soil. A few species are 

 pathogenic, including the organisms causing typhoid fever, 

 paratyphoid fever, dysentery, and certain types of food 

 poisoning. One species, the Bacterium coli, is frequently 

 used as an index for the determination of the presence of 

 sewage in water. 



Pasteurella. — The organisms of this genus are all rod- 

 shaped cells, Gram-negative, and show bipolar staining. 

 They have very slight powers of fermentation. Members 

 of this genus produce many diseases in man and animals, 

 including the bubonic plague of man and the hemorrhagic 

 septicemias of animals, such as fowl cholera and related 

 diseases in swine, sheep, cattle and horses. 



Hemophilus. — The organisms belonging to this genus are 

 minute, parasitic. Gram-negative rods, which grow in the 



Fig. 24. — Bacterium. Fig. 25. — Pasteurella 



laboratory only in special media, preferably containing 

 hemoglobin. The most important species is Hemophilus 

 influenzae, the organism which has been supposed to cause 

 influenza and which is quite certainly associated with many 

 cases of the disease. 



Lactobacillus.— The cells are rod-shaped, often long and 

 relatively slender, Gram-positive, and nonmotile. Some 

 species have very short cells and are almost eoccuslike. No 

 endospores are developed. Acid, particularly lactic acid, 

 is usually produced in considerable quantities from carbo- 

 hydrates. Many of the species prefer to grow in the ab- 



