Chapter I —19— Taxonomy 



Drechsler (97) suggested that the nature of the curvature of the 

 spirals can be utilized as a distinguishing character. Krassilnikov, 

 however, observed that most forms turn counter-clockwise (the reverse 

 under the microscope), and only few in the reverse order. The nature 

 of the medium is of great importance in this connection, thus making 

 this character of doubtful taxonomic significance. 



The fragmentation spores or the true conidia of members of the 

 genus Stre-ptoviyces are spherical, oval, and elongated, whereas the seg- 

 mentation spores or the oidiospores, characteristic of the Nocardia, are 



i 



Fig. 5 b (seep. 18). 



usually cylindrical. The nature of these spores, especially the elongated 

 ones, varies only occasionally. The manner of sporulation is constant. 

 Because of these properties, the morphological characters form the most 

 reliable basis for the separation of these organisms. 



Cultural characteristics.— The growth and reactions of actinomycetes 

 in culture media have been utilized most extensively for characteriz- 

 ing the individual species. There is, in this respect, however, con- 

 siderable overlapping among the different forms, and one is frequently at 

 a loss to know where to place a freshly isolated culture. Among the 

 most important cultural properties are the following: 



1 . Shape and structure of colony, nature of vegetative growth, and appearance 

 of aerial mycelium. 



2. Anaerobism vs. aerobism, a very unstable property that cannot be sharply 



