SOIL ACTINOMYCES 289 



The systematic position of actinomyces has not been satisfactorily 

 defined. These organisms are classified more often with bacteria, 14 in 

 some cases with the fungi (among the Hyphomycetes, under Oospora, 15 

 or as a Mucedineous group with tendencies towards an erect Isariod 

 habit 8 ) and in some cases as a separate group forming the connecting 

 link between the bacteria and the fungi. 9, u - 16 The actinomyces may 

 look like true bacteria in ordinary stained preparations, due to the fact 

 that the mycelium is very fine and is readily broken up into various 

 fragments, and the conidia look very much like bacterial cells. In 

 unstained preparations, however, such as are used for the direct exami- 

 nation of the colony, or when stained by some special method, s ' 17 

 the branching and manner of spore formation can be seen to resemble 

 that of a true fungus. 



Physiologically, the actinomyces are differentiated from both fungi 

 and bacteria. The fungi are characterized, as a rule, by having greater 

 resistance to acids than the bacteria. The actinomyces, with some few 

 exceptions, are even more sensitive to acids than the majority of the 

 bacteria developing on the common plate. A large number of bacteria 

 are characterized by the formation of various gases from carbohydrates ; 

 the actinomyces are not known to form any gas from carbohydrates 

 except C0 2 , which is a product of the energy metabolism of most living 

 forms; in this respect they behave like the fungi. The apparently close 

 relationships which the actinomyces have with both bacteria and fungi 

 led to the assumption that the actinomyces should be looked upon as 

 the ancestral form of both bacteria and fungi, according to the follow- 

 ing scheme : 



Yeasts 



/ 



mycelial forms — > Oidium — > Hyphomycetes 



, . Z 1 



Actinomyces 



bacillary forms — > Mycobacteria — > Corynebacteria — > Bacteria 



The fact seems to be definitely established that trre actinomyces are 

 not bacteria. But they cannot be classified unreservedly with the fungi, 



"Bergey, 1923 (p. x). 



16 Savageau and Radais. Sur les genres Cladothrix, Streptothrix, Actinomy- 

 ces. Ann. Inst. Past., 6: 242-273. 1892. 



16 Claypole, E. On the classification of the streptothrices, particularly in 

 their relation to bacteria. Jour. Exp. Med., 17: 99-116. 1913. 



17 Waksman, S. A., and Curtis, R. E. The actinomyces of the soil. Soil Sci., 

 1: 99-134. 1916; also Waksman, 1919 (p. 288). 



