456 MEDICAL MYCOLOGY 



In E. farinulentum, a very curious variant developed in a blood agar slant, 

 where the aleurospores were produced in A^ery large numbers but never 

 matured. Finally, the whole mass formed a clump, suggestive of a nodular 

 organ. The mycelium remained of normal diameter, thus differentiating it 

 from a pleomorphic mycelium. 



Pleomorphism. — While some other groups of fungi show slight changes 

 after continued cultivation on various media, these are much less spectacular 

 than those of the dermatophytes. These changes should be clearly distin- 

 guished from the ordinary changes which are common to all fungi. In culture 

 any fungus undergoes changes in appearance from youth through the adult, or 

 normal, form to senile degeneration. For example, if the giant colony nor- 

 mally forms concentric folds, these may be contorted by variable growth 

 rates in the senile colony. Similarly a colony which is only crackled in the 

 normal adult form may be deeply fissured in the senile stage. The juvenile 

 form reappears when the spores from old cultures are transferred to fresh, 

 suitable media, and it repeats the same cycle of changes. 



In true pleomorphism, subcultures retain all the characteristics of the 

 pleomorphic mycelium and do not revert to the juvenile stage. In most derma- 

 tophytes which have been growing from 4 to 6 weeks on sugar-containing media, 

 there appears, usually at the point of inoculation, sometimes elsewhere on the 

 colony, a delicate tuft of white mycelium which gradually spreads over the 

 surface like a contaminating organism. This may even grow beyond the edge 

 of the colony. Microscopic examination shows it to be altogether different 

 from the normal mycelium of the original colony. It usually bears much 

 fewer spores, closterospores and ehlamydospores being absent, often aleuro- 

 spores also. When this pleomorphic mycelium is transferred to fresh media, it 

 continues to exhibit only the characters of the pleomorphic mycelium, although 

 it develops a different colony form (usually a smooth white disc). This condi- 

 tion appears to be irreversible. 



In some cases, a loss of viinilence accompanies this form of pleomorphism. 

 In Ectotrichophyton mentagrophytes var. radiolatnm (Catanei 1930), the 

 initial inoculation of pleomorphic mycelium produced the typical lesion of this 

 species in a guinea pig, but the pleomorphic mycelium isolated from this lesion 

 produced an epidermal lesion without invading the hair. On the other hand, 

 inoculation directly from guinea pig to guinea pig by infected hair from a 

 lesion caused by pleomorphic mycelium continued to produce a typical lesion, 

 without attenuation. From pleomorphic mycelium of Microsporum felineum, 

 Langeron and Talice (1930) obtained a typical lesion and reisolated only pleo- 

 morphic mycelium from the lesion. In the pleomorphic mycelium of Tricho- 

 phyton Sahouraudi (T. acuminatum), a species which very rarely becomes pleo- 

 morphic, Catanei (1931) found decreased pathogenicity for the guinea pig and 

 reisolated pleomorphic mycelium from the lesion. 



The pleomorphic mycelium looks so different from that in a freshly iso- 

 lated colony that unless one is familiar with the early stages in the develop- 

 ment of such a colony, there is danger of regarding the freshly isolated colony 



