SOIL ACTINOMYCES 305 



by the composition of the medium and age of culture. When or- 

 ganisms are named merely on the basis of pigment production on 

 complex media (-4. chromogenus, A. snlfureus, etc.), or on the basis 

 of color of aerial mycelium (A. albus, A. niger), on the basis of ring 

 formation in aerial mycelium (A. annulatus), we are merely utilizing 

 variable properties of the organisms as some distinguishing charac- 

 ters. When the organisms are transferred to other media, or even 

 when cultivated continuously on the same medium, the pigment may 

 change and rings may no longer be formed. The species thus lose 

 their distinguishing characteristics and become other species. In addi- 

 tion to using a group of morphological and physiological characteristics 

 which are commonly employed for the species determination, one must 

 also allow for the variability of the organisms. Observations should be 

 made of the morphological and physiological characteristics on synthetic 

 media for a large number of generations. Such characters as pigment 

 production may change. A. verne produced, when originally isolated 

 from the soil, a beautiful green pigment on Czapek's agar, but lost the 

 property in a few months when grown on synthetic media; after several 

 years, it gained the property of producing a brownish-purple pigment on 

 the same medium. The property of producing aerial mycelium may be 

 lost and the character of growth changed. A. halstedii, when freshly iso- 

 lated from the soil, produced a dark growth with a mouse-gray aerial 

 mycelium on Czapek's agar; on continued cultivation on artificial 

 media, the property of forming an aerial mycelium was lost altogether, 

 and the growth became dark brown and lichnoid in appearance. In 

 some instances, organisms that lost the power of forming aerial mycelium 

 regained it after cultivation in sterile soil. 



Similar variability is found in the rapidity of gelatin liquefaction, 

 production of soluble pigment, action on milk, oxygen requirement, and 

 odor production. One can readily observe in some actinomyces cul- 

 tures the formation of sectors, differing in one respect or another from 

 the rest of the growth. On transferring from such a sector to a fresh 

 medium, an organism may be obtained which differs from the mother 

 culture in some character such as color, presence of aerial mycelium, 

 zone formation, pigment, etc. Lieske has thus isolated five new forms, 

 in addition to the original, which were distinguished from one another 

 by at least one character. Although the claim is put forth that pure 

 spore cultures were used, no mention is made of the use of such a pro- 

 cedure as the Barber pipette, which would absolutely insure a single- 

 spore culture. 



