CLASSIFICATION OF THE BACTERIA 41 



Order Actinomycetales 



The organisms belonging to this order usually have the 

 cells somewhat elongated, frequently filamentous, and with 

 a decided tendency to the formation of branches. In some 

 genera a definite branched mycelium is developed. The 

 cells frequently show swelling, or are clubbed or irregular 

 in shape. Endospores are not produced, although conidia 

 are formed 1y some genera. Many of the genera are Gram- 

 positive and all are nonmotile. Some species are parasitic 

 in animals or in plants. Most of the species are aerobic. 

 The genera belonging to this group are Actinomyces, Myco- 

 bacterium, Corynebacterium, and Pfeifferella. ^ 



Actinomyces. — The organisms belonging to this group 

 form fine threads (or mycelium,) which break up into 

 short segments which function as spores or conidia. Some 

 of the species are parasitic, one, the Actinomyces bovis, pro- 

 ducing lumpy jaw in cattle. Many other species are widely 

 distributed in the soil, apparently growing upon decaying 

 roots and similar organic matter. 



Mycobacterium. — These organisms are slender rods 



which are stained with difficulty, but when once stained are 



resistant to decolorization by acids, that is, they are termed 



acid fast. The cells are sometimes swollen, showing club 



shapes or forked forms, occasionally the cells are branched. 



They are nonmotile and Gram-positive. Some of the 



species are present in the soil, a few are pathogenic to man 



and animals. The most important of the diseases caused 



are tuberculosis and leprosy in man, and paratubercular 



dysentery in cattle. 



1 Other genera are ActinohaciUus, one species producing the disease 

 called actinobacillosis in cattle; Leptotrichia found in the mouth; 

 Erysipelothrix producing disease in man and animals, particularly 

 the disease swine erysipelas; and Fusiformis, including certain mouth 

 and throat forms, some of them associated with diseases of the throat 

 and the mouth. 



