THE FUNGUS OF FAVUS 235 



of levulose or J per cent, of common salt. In order to 

 obtain pure cultures dry media only must be employed, and 

 they must accordingly have been kept in a warm place for 

 a considerable time before use. All other micro-organisms 

 which might spoil the pure culture of favus require a tolerably 

 large amount of water, and soon cease to grow upon very 

 dry soils. The Achorion euthythrixfoms dense woolly white 

 furs, half a centimeter in height, upon the nutrient medium, 

 and grows but a short way into its substance, whereas 

 the growth of Achorion dicroon lies for the most part in 

 the medium and only raises a thin coating of mycelium 

 .above the surface. The Achorion atacton occupies an inter- 

 mediate position between the other two. Those varieties 

 of favus fungus which are marked by their deep growth 

 in artificial cultures grow also into the hair-follicles and 

 are more difficult to treat. 



Gelatine is liquefied very late and only very slightly by 

 the growth of the favus fungi. On agar plates there 

 develop in twenty-four hours at incubation heat, according 

 to Plaut, very small shining fibres resembling cotton wool, 

 which are recognisable under the microscope as minute 

 masses of conidia. In forty-eight hours the colonies have 

 changed to round milk-white opaque discs possessing a 

 border of very fine and quite short threads. On potato 

 Plaut obtained, at incubation temperature, an irregular dis- 

 coloration on the site of inoculation, from which the fun- 

 gus grows into the substance of the potato. Similar 

 -coatings to that upon potato appear on boiled white of egg, 

 .and on blood-serum a greyish-white, thin, coherent film 

 develops below the surface and sends out long thin pro- 

 cesses downwards and parallel to it. The serum is neither 

 liquefied nor discoloured (fig. 88). 



[Microsporon furfur is found in the yellowish or brownish 

 ,-scaly patches on the skin in pityriasis versicolor. When 

 some of the scales are examined under the microscope in a 



