386 MEDICAL MYCOLOGY 



the entire surface. If a fragment of this pleomorphic mycelium 

 is planted on a fresh medium, the cultures obtained are like the 

 pleomorphic mycelium, and these characteristics are retained on 

 subsequent repeated transfer. Pleomorphic forms do not revert 

 to the normal once they have been isolated. 



The most striking feature of these pleomorphic colonies is that 

 the majority of them remain completely sterile, whereas other 

 species may form chlamydospores or may bear small, little differ- 

 entiated, lateral spores. For this reason pleomorphic forms of the 

 different species are very similar to each other, and identification 

 has been difficult and very confusing. Many are so similar, in 

 fact, that some workers question the plurality of species among 

 ringworm fungi. 



Variation in this tendency to produce pleomorphic forms exists 

 among these fungi. Pleomorphism is common among small- 

 spored, animal-infecting species of Trichophyton and among spe- 

 cies of Microsporon from animals but is rare or non-existent 

 among species of Trichophyton attacking man. Tate (1929) 

 states that it is not known to occur in Microsporon aiidoidni or in 

 Trichophyton radians and T. denticulatum. 



According to Sabouraud, nutritional and temperature factors 

 most favorable for growth are also most favorable for the develop- 

 ment of pleomorphic forms. The presence of about 4% of carbo- 

 hydrates in the medium and constant temperatures of 30° to 37° C 

 induced pleomorphic changes, whereas media with 3% of peptone 

 and no carbohydrates tended to prevent pleomorphic develop- 

 ment. 



When Langeron and Milochevitch (1930) grew Sab our audit es 

 asteroides ( the generic termination ites should be limited to genera 

 of fossils), S. granulosus, S. lacticolor, and S. gypseus, all of which 

 are pleomorphic on sugars, on cereals, straw, dung, or synthetic 

 media enriched with dextrin or soluble starch, pleomorphic forms 

 did not appear. They concluded that monosaccharides and disac- 

 charides are toxic and that these sugars induce pleomorphic 

 change, whereas polysaccharides and the colloidal complexes of 

 the natural substrata are not toxic and may be used without first 

 being cleaved. 



Emmons (1932) cultured Achorion gypseuni on horn, starting 

 with a single aleurospore. Six distinct pleomorphic variants arose 

 from the progeny, and all were so different that, if they had been 



