306 An Introduction to Medical Mycology 



either ease, the manifestation is usually mildly inflammatory, the affected 

 skin being dull red, scaly and thickened. The interdigital webs, the sides 

 of the feet, the inner surfaces of the thighs, the hands and the nails of 

 either the hands or the feet or both are the usual sites. Many patients com- 

 plain of severe itching not confined to the areas of the eruption. Uncom- 

 monly, the smooth skin shows erythematous plaques or widespread gyrate 

 lesions. 



(b) Immunologic reactions.— The usual delayed reaction to trichophy- 

 tin is slight or absent in patients with an infection due to T. purpureum. 

 There is sometimes an immediate wheal response (see Chapter XXX, 

 "The Trichophyton Test"). 



(c) Microscopic features.— Relatively few fungous filaments are noted. 

 Repeated tests may be needed to demonstrate presence of fungus. When 

 the hair follicle is invaded the fungus is seen to be an ectothrix Tricho- 

 phyton. 



(d) Cultural characteristics.— In the primary growth, the culture at 

 first is fluffy, pure white and hemispheric. Later the edge of the colony is 

 less fluffy, becoming almost velvety. Sometimes the central umbo is lacking. 

 Radial grooves may appear. The back of the colony soon develops a typ- 

 ical rose-purple color. This color gradually spreads to the edge of the older 

 colony and may later be noted in varying degree throughout the colony. 



If the aerial growth is abundant, the colony appears white and fluffy and 

 the rose-purple color can only be seen from the back. When the growth is 

 more sparse the color may be seen from the top. This accounts for many 

 of the variations in the color of the colony. The appearance of the colonies 

 with a minimal aerial growth varies from powdery to granular. 



(e) Culture mount.— Vegetative filaments are simple and show little 

 variation. The microconidia are produced in grappes or along the mycelium 

 as hvphae sporiforae. In fluffy colonies microconidia predominate. There is 

 little evidence of fuseaux (except when they are searched for). In gran- 

 ular colonies abundant fuseaux may be seen, and microconidia are scant. 

 Racquet mycelium and chlamydospores will be observed if the nutrition of 

 the medium is reduced. 



(f) Filtered ultraviolet rays.— Without experience one has difficulty 

 in distinguishing between T. gypseum and T. purpureum. In an early col- 

 ony of T. purpureum the color is a bright, light blue, which is present 

 throughout the colony or, if the colony is very fluffy, at the periphery alone. 

 In older colonics the light blue border is characteristic. 



(g) Animal inoculation.— This is occasionally successful. Reiss, work- 

 ing in our laboratory, Found that rabbits which had been castrated or had 

 received x-ray exposures to the abdomen could be infected at will. 



