Tinea tonsurans is peculiarly a disease of early life. This affection is practically confined to children, and in the form of ringworm of the scalp is one of the most obstinate and contagious of complaints. The disease is due to the presence of a fungus—the tricophyton tonsurans—which grows in the internal root-sheath within the follicle, and the fine mycelium fila ments penetrate into the hair between the fibres. These filaments are composed of cylindrical, tube-like bodies united in chains. At the surface of the hair the spores of the tricophyton are collected into little globular masses called conidia, and in very old-standing cases these are also seen to fill almost the whole thickness of the hair. As a consequence of the presence of the parasitic fungus the hairs are greatly thickened ; their colour changes to a dull gray tint, and their brittleness causes them to break off short at a point immediately above the follicle out of which they issue. The fungus is seen not only in the substance of the hair, and coating their shafts, but also as a more or less continuous layer on the sur face of the scalp. Through this covering the free ends of the stubbly hairs can be seen as black points. Later, as the parasitic matter accumulates, the stumps of hair become completely ensheathed in the mycelium coat ing so that their situation is only shown by a projection of the surface of the layer. Bazin has compared the appearance thus produced to that of a surface covered with hoar-frost.
In very old-standing cases, acute inflammation may be set up in the hair-follicles. This may lead to complete destruction of the hairs, so that the part of the scalp affected remains partially bald.
Symptoms.—On the scalp ringworm is seen in more or less circular patches. These in the earliest stage are slightly raised above the surface, and cause considerable itching. The hairs are not broken off, and have almost a natural appearance ; but they will be found to be very brittle, so that they generally break if an attempt is made to extract them. As the disease proceeds the patches become distinctly circumscribed, and of a pale fawn or slate-gray colour. Their surface is covered by a thick scurf
formed of epithelial scales mixed with the fungoid growth. This scurf gives a frosted appearance to the patch, and adheres to the shafts of the hairs as these emerge from the follicles. The patches are not entirely covered by the short bristly hairs, for in many places these have fallen out, leaving the surface bare. Those which remain are short and twisted. They look as if cut off about a line or two above the surface of the scalp ; and are thickened, dull in colour, and sometimes loose in their sockets. If the scurf has accumulated to a great thickness, the ends of the hairs may be completely concealed from view.
The number of patches existing at the same time varies. Sometimes they are very numerous ; indeed, in certain cases, the disease takes on a diffuse form, in which little groups of scaly patches with bristly stumps of hairs are seen scattered over the surface of the head.
When the tinea is seated on the skin of the body it is called tinea cir cinata. This is also a very common form of the disease, and is generally found on the face and neck, although it may occupy any part of the body or limbs. It is seen as a slightly elevated, roundish patch, of a light- red colour, and of the size of a small pea. This begins to extend at its edges, and as the circumference spreads, the central part fades and becomes less prominent, so that the circular patch is converted into a ring which con tinues to enlarge. With a lens the surface affected is seen to be covered with branny scales ; and fine vesicles are noticed at the margins. If two adjacent rings happen to touch one another, morbid action at the point of contact undergoes no further extension. In this way curiously irregular shapes are often produced. In the central part of the ring the skin, although of comparatively healthy appearance, has yet a yellowish tint, and a roughened look from small scales. These spots cause a great deal of irritation, and the fungus is no doubt often conveyed by the child's nails from the body to the scalp.