MORPHOLOGY OF ACTINOMYCETES 357 



since his methods did not differentiate between nuclei and volutin 

 granules, his findings have been generally discounted by critical bac- 

 teriologists. Recently, Newcomer and Kenknight " have demon- 

 strated by the Feulgen stain what appear to be nuclei, definite and 

 discrete. Von Plotho " has found discrete nuclei by the Feulgen 

 method in the conidia and somewhat less discrete nuclei in the my- 

 celium. Badian ^ has also demonstrated what appear to be nuclei 

 in the spore-bearing mycelium and in the conidia. 



In addition to the arthrosphores or fragmentation spores many 

 species of actinomycetes reproduce by the formation of conidia on 

 aerial hyphae. Spore formation is, however, very irregular, with 

 many species failing completely on some media. Cultures which 

 have not been transplanted for some time frequently fail to form 

 spores in the first subculture. It is not an uncommon experience to 

 find conidia develop rather suddenly on a strain which has not shown 

 any aerial mycelium during many months of subcuitivation, and old 

 laboratory strains, w^hich formed conidia when first isolated, fre- 

 quently have a tendency to lose the ability to form conidia readily. 

 The formation of aerial mycelium and conidia is manifested by the 

 development of a fine powdery coat on the surface of the culture. 



The mechanism of spore formation and the arrangements of the 

 sporogenous hyphae have been studied in some detail by Drechsler.^ 

 According to this author, conidia are formed by the development of 

 septa in the terminal portions of the filaments. These septa are at 

 first thick and stain deeply. Then a division occurs transversely 

 through the septa separating the terminal portion of the filament 

 into cylindrical segments which later may become rounded. But 

 Lieske ^* believes that true septa are not formed. Instead, vacuoles 

 or empty spaces appear in the hyphae, dividing the protoplasm into 

 many segments which become separated by constriction to form the 

 conidia. According to this author, the aerial spores are not true 

 conidia, but merely a further development of fragmentation spores. 

 It would seem, however, that the aerial mycelium and its spores are 

 too minute to permit such fine differentiations to be made with 

 certainty. It should be noted, however, that the presence of septa 

 in the pathogenic species previous to formation of the fragmentation 

 spores is definitely established. 



A very striking character of the spore-bearing filaments is their 

 tendency to be spirally twisted. This is more marked in some species 

 than in others. Drechsler has noted that in some cases the filaments 

 are coiled to the right, in other cases to the left, and he has main- 

 tained that this character is constant for the species. It is not al- 



