168 GENERAL SYSTEMATIC BACTERIOLOGY 



conidia may be developed, but never endospores. Without granules of free 

 sulphur and without bacteriopurpurin. Never producing a pseudoplasmodium. 

 Always non-motile. 



The description was emended by the Committee of the Society of 

 American Bacteriologists to read as follows: 



Cells usually elongated, frequently filamentous and with a decided tendency 

 to the development of branches, in some genera giving rise to the formation of 

 a definite branched mycelium. Cells frequently show swellings, clubbed or ir- 

 regular shapes. No pseudoplasmodium. No deposits of free sulphur or iron. 

 No bacteriopurpurin. Endospores not produced, but conidia developed in some 

 genera. Usually Gram-positive. Non-motile. Some species are parasitic in 

 animals or plants. Not water forms. Complex proteins frequently required. 

 As a rule strongly aerobic, (except for some species of Actinomyces and the gen- 

 era Fusiformis and Leptoti icMa) and oxidative. Growth on culture media often 

 slow; some genera show mold-like colonies. 



This description is also used by Bergey et at. (1923, p. 337). 



The committee recognized two families as belonging to this order, 

 Actinomycetaceae and Mycobacteriaceae. The committee's suggestion 

 is followed in the present volume. 



Actinomycetes. This family designation of the thread fungi was 

 probably first proposed by Balbiani (1886, p. 542). Later Lachner- 

 Sandoval (1898) included in it the single genus Actinomyces Harz. 

 Lehmann and Neumann (1901, p. 127) include within the family three 

 genera, Corynehacterium L. and N., Mycobacterium L. and N., and 

 Actinomyces Harz. They give the following description of the family. 



Delicate thread organisms, without chlorophyll, with true branching, in 

 some cases with an abundant branched mycelium and the formation of conidia. 

 Young cultures often show only unbranched rods resembling bacteria which 

 can in no way be differentiated from the ordinary fission fungi. According to 

 many authors there is a tendency to the formation of clubs or knobs at the ends 

 of the threads. 



The three genera may be differentiated by the following key: 



A. Cultures showing ordinary bacterial characters, flat or medium, micro- 



scopically rods with swollen ends. Corynehacterium L. & M. 



B. Cultures on solid media more or less folded. 



I. Usually short slender rods only, seldom short branched filaments, 

 without aerial mycelium and without aerial conidia. Acid fast — 

 Mycobacterium L. & N. 

 II. Mycelial filaments long, often bent, without sheath, with true branch- 

 ing. Many species produce conidia or aerial hyphae. Not acid 

 fast — Actinomyces Harz. 



