42 AGRICULTURAL AND INDUSTRIAL BACTERIOLOGY 



Corynebacterium. The cells are slender, often slightly 

 curved rods with a tendency toward the formation of clubs, 

 and containing granules which give the cells when stained 

 a barred or irregular appearance. They are not acid fast 

 but are Gram-positive and aerobic. Most species are para- 

 sites, the most important being Cory neb act eriumi diph- 

 theriae, the cause of diphtheria in man. 



Pfeifferella. These organisms are nonmotile rods, slen- 

 der, and Gram-negative, staining poorly, sometimes form- 

 ing threads, and showing a tendency toward branching. 

 When grown upon potato in the laboratory they develop a 

 characteristic honeylike growth. The most important 

 species is Pfeifferella mallei, the organism which causes the 

 disease glanders in the horse. 



ORDER SPIROCHAETALES 



The organisms belonging to this group in many respects 

 resemble the protozoa, and may be regarded as intermediate 

 between the true bacteria and the protozoa. They are all 

 more or less curved rods, frequently very slender. Many 

 species are motile but there has been no definite demon- 

 stration of flagella. They multiply either by longitudinal 

 or transverse fission. It is probable that in some cases 

 they have a relatively complex life history . Several genera 

 have been described, the most important being Treponema. 



Treponema. The organisms^ belonging to this genus are 

 exceedingly slender spiral rods, motile by means of flexuous 

 bending of the body. The most important species is Tre- 

 ponema pallida, the cause of the disease syphilis in man. 



