The fungus is abundant in recent cases; it is extremely
scarce in cases of old standing. The mycelial tubes in fresh cases are generally straight, have often a double contour, and the segments are rectangular, their breadth being 3½ to 4½ microns; branching is not infrequent; the spores are rather large, roundish, and present a double contour; they never collect in clusters. In chronic cases degeneration forms of the fungus are met with : the mycelium may be banana-shaped, presenting several constrictions; or long strings of ovoid elements may be seen.
The fungus is best grown by using maltose media. In cases of old standing, owing to its scarcity in the lesions, it is grown only with great difficulty. The material to be inoculated must be taken from the edges of the lesion. The growth begins to be visible after five to nine days; the rate of growing being very slow. After three to four weeks the colonies are about one half inch and even more in diameter. The colonies are orbicular-shaped, hard, with a pulverulent surface. The colour at first is greyish-yellow, with occasionally a greenish tinge; later it becomes a greenish white.
I have tried inoculation experiments on man with pure cultures of the fungus, but without any success. Sabouraud has also failed to reproduce the disease.
Trichophyton Perneti.—The fungus is microscopically indistinguishable from Trichophyton cruris: the cultural characters, however, are quite different, the fungus growing much more rapidly and the cultures presenting a delicate pinkish colour, which is generally lost in sub-cultures. This variety is found very rarely: clinically the lesions caused by it are identical with those caused by Trichophyton cruris. I proposed for the fungus the name T. perneti, as Pernet was the first to grow this species from a case of tropical trichophytosis. It was found, however, in only 2 per cent, of my cases.
