Waksman — 74 — Actinomycetes 



small unicellular mycelium which soon divides into bacteria-like ele- 

 ments; these multiply by cell division in the manner characteristic of 

 corynebacteria. Two subtypes were recognized for the R-form: the soft 

 or s-t)'pe and the hard or h-type. The s-type, which is the original, pro- 

 duces a soft, pasty growth of red color; the bacteria-like elements are 

 usually short, blunt, little-branched, and partly acid-fast. The h-type 

 produces a dry, crumbly growth, adhering firmly to the medium and 

 consisting of longer and more slender cells, less acid-fast than the s-type 

 and with a marked tendency to form long filaments. The h-type arises 

 spontaneously in, and can also be produced experimentally from, cul- 

 tures of the s-type. Exposure of the h-type to ultraviolet rays gave rise, 

 for example, to a yellow and a white variety of the s-type. The s- and 

 h-types were believed to correspond to the plane and perrugose variants 

 of mycobacteria, and were also comparable to the smooth and rough 

 variants among other bacteria. The F-form represents a stabilization of 

 the initial mycelial stage of the R-form. It is an actinomyces-like organ- 

 ism, consisting of long, delicate, branching hvphae, with a well-devel- 

 oped aerial mycelium, and without any tendency to divide by septa into 

 bacteria-like elements. The F-form was found to arise spontaneously in 

 old cultures of the s-type, but not in the h-type. Its appearance did not 

 seem to be influenced by external factors. 



Novak and Henrici (326) reported the appearance of a yellow 

 staphylococcus in a Berkefeld filtrate of a broth culture of a saprophytic 

 actinomyces. Under the microscope, the staphylococcus was observed 

 to change first into rods, then into long, branched filaments which could 

 not be distinguished from true actinomyces mycelium. The reverse 

 changes were also observed. The coccus was found to dissociate first 

 into S- and R-forms, then into filterable G-forms. These observations 

 were believed to support the theory that staphylococci are related to the 

 actinomycetes. As pointed out above Krassilnikov described the 

 micrococcus as merely a stage in the normal development of the nocardia 

 rather than as an abnormal mutant. 



Certain of the characters of actinomycetes appear, however, to be far 

 more constant than those listed above. These include the formation of 

 aerial mycelium on specific media, the formation, nature, and direction 

 of the spirals, the manner of spore formation, and the size and shape of 

 spores. Only seldom do variations occur in such specific characteristics 

 as abundance of the mycelium, lengthening or shortening of hyphae, 

 and size of spores (242). 



Cultural variations— Among the cultural variations, those of pig- 

 mentation are most striking, since pigments are widely distributed 

 among actinomycetes. This is of particular significance in view of the 

 fact that differentiation of many species is based upon the nature and 

 intensity of the pigment. Even the major subdivisions of some of 

 the groups of actinomycetes have been based upon pigmentation, as was 

 done by Sanfelice, Duche, and others. Evidence of this is found in 



