CLASSIFICATION OF THE ACTINOMYCETES 5 



nature of the aerial mycelium, the nature of the sporulating branches or 

 sporophores, and the nature of the spores. 



Among the physiological and cultural properties essential for characteri- 

 zation purposes, pigmentation of the vegetative and aerial mycelium is 

 most important; the formation of soluble pigments, both in synthetic and 

 in complex organic media, is also significant. Am ^ng the other characteris- 

 tics, one may list utilization of starch (diastase formation), various proteins 

 (protease), sucrose (invertase), cellulose (cellulase?), and a variety of other 

 carbon compounds. Reduction of nitrate, production of odor, and coagula- 

 tion of milk (acid production) are among the other characteristics. Still 

 other activities include the utilization of fats, paraffin, and phenol. 



The various fermentation properties, comprising the utilization of sugars 

 and related compounds, with and without the formation of acids, can sup- 

 ply additional information for species differentiation. The antagonistic ac- 

 tivities and the ability to produce antibiotics have recently come into popu- 

 lar use for the description of actinomycetes. Their sensitivity to phages and 

 to known antibiotics is also of considerable importance in establishing 

 specific differences. 



Many species of actinomycetes have been described in the literature as 

 pathogenic to plants or animals. The fact that such cultures were isolated 

 from infectious diseases is no proof, however, that they are the causative 

 agents of such diseases. 



Many of the earlier and even some of the more recent descriptions of 

 actinomycetes are superficial, and it is often difficult to compare the charac- 

 teristics of a freshly isolated culture with those of the published description. 

 No wonder, therefore, that it has been much easier to give a fresh culture a 

 new specific name rather than to attempt its identification with a species 

 already described. 



In identifying cultures of actinomycetes, extensive use has been made, 

 therefore, of their morphological and physiological properties. The cultural 

 characteristics, notably growth characteristics on various organic and syn- 

 thetic media, formation of soluble pigments, proteolytic and diastatic 

 properties, utilization and transformation of specific organic and inorganic 

 compounds, have received particular attention. Pridham and Gottlieb em- 

 phasized recently that the utilization of carbon compounds should receive 

 greater consideration for species determination than hitherto. All the partic- 

 ular species tested were able to utilize d-glucose, d-mannose, dextrin, and 

 glycerol, but not erythritol, phenol, cresols and the sodium salts of formic, 

 oxalic, and tartaric acids. The utilization of such compounds, however, as 

 rhamnose, raffinose, xylose, lactose, mannitol, dulcitol, inositol, and the 

 sodium salts of acetic and succinic acids, was selective. 



It has been suggested that rather than single species, group species should 



