258 An Introduction to Medical Mycology 



appearance which may be due to temperature (season), moisture, or other 

 factors. It is difficult to obtain a characteristic colony of T. violaceum or 

 T. crateriforme during the winter months. In winter the early growth of 

 different strains of T. purpureum is fairly uniform, but in summer consid- 

 erable variation in the gross cultural characteristics is common. 



2. PLEOMORPHISM 



After prolonged isolation on a culture medium, many fungi assume a 

 vegetative character, as evidenced by a white fluffy growth almost always 

 starting at the point of inoculation. Within a short time the entire colony 

 may be covered. Some fungi, such as M. lanosum, develop this character 

 after a short time, while other fungi, such as T. violaceum, never assume 

 the vegetative form. This result of degeneration, old age or monomorphism, 

 whichever it may be, is difficult to overcome once it has appeared. Sub- 

 culturing sometimes causes the micro-organism to assume its original 

 nature, but in such instances the growth is probably not truly pleomorphic. 

 It has been suggested by Sabouraud, Catanei and others that this state 

 may be present in a primary culture; thus T. interdigitale is considered by 

 some to be a degenerate form of the granular type of T. gypseum. We be- 

 lieve T. interdigitale is a variant of T. gypseum. The development of pleo- 

 morphism may result in a loss of virulence, as evidenced by the degree 

 of involvement of infected tissue. Catanei has performed experiments sub- 

 stantiating this. 



BIBLIOGRAPHY 



Cantanei, A.: Sur le parasitisme ties poils dans l'infection experimentale provoquee par des 

 cultures pleomorphiqu.es dun Trichophyton gypseum, Compt. rend. Soe. de biol. 105:348, 

 1930. 



