Tyndall Phenomenon and Tinea

TYNDALL PHENOMENON, a phenomenon or effect, consists in the fact that a bright beam of light passing through certain transparent bodies and viewed in a direction perpendicular to the path of the light rays is visible in the corresponding transparent body as a certain turbid strip, which at first glance resembles the light strip obtained during fluorescence. The Tyndall effect is observed mainly in colloidal solutions, and, as more detailed studies have shown, the light emitted in the direction perpendicular to the path of the rays turns out to be polarized light. A deeper study of the Tyndall phenomenon under a microscope was carried out by Siedentopf and Zsigmondy, who showed that the scattering of light by colloidal solutions of gold or platinum depends on the diffraction of light on individual grains of the colloid. These grains can be seen under a microscope as luminous points, even if their dimensions are significantly smaller than the dimensions of bodies that can be seen under a microscope. On this principle, Siedentopf and Zsigmondy founded a new method for studying ultramicroscopic particles, the so-called ultramicroscopy. Later extensive studies by Cabannes, Rayleigh, and others showed that the phenomenon of diffraction can also occur near molecules of solid and liquid substances that do not have a colloidal character. Due to the smallness of the molecules, the amount of scattered light in this latter case is significantly less than in colloidal solutions. The Tyndall phenomenon can be confused with the phenomenon of fluorescence, however, there is a sharp distinction between these two phenomena; this is manifested primarily in the fact that in the Tyndall phenomenon, simple scattering of light is observed, not accompanied by a noticeable change in the wavelength of the incident light. In fluorescence, on the contrary, a sharp change in wavelength occurs (Stokes' law), and the light emitted during fluorescence has a longer wavelength than the light causing the fluorescence. Light in fluorescence is non-polarized light, whereas light in the Tyndall phenomenon is polarized. Nephelometry (see) is based on the Tyndall phenomenon, specifically on the measurement of the intensity of light scattered by suspended particles (Tyndall light). The Tyndall phenomenon explains the coloration of many bodies. For example, colloidal solutions of gold, containing ultramicroscopic particles of metallic gold in a suspended state, show phenomena of coloration depending on the fact that light rays of different wavelengths diffract in different ways on the gold particles.

TINEA (Latin: moth, French: teignes—fungi), a name previously applied to various kinds of scaling processes on the scalp; later, the word Tinea began to denote exclusively fungal diseases of the skin, mainly trichophytosis. At the present time, in generally accepted dermatological nomenclature, the name Tinea is applied only in relation to certain tropical dermatomycoses: tinea imbricata, cruris, and others. Tinea cruris, a dermatomycosis similar to the so-called eczema marginatum (Hebra), caused by the fungus Epidermophyton inguinale Sabouraud (see Epidermophytosis). Tinea cruris is very common in tropical countries, and the Trichophyton cruris Castellani and Trichophyton perneti isolated there from these lesions are apparently identical to Trichophyton inguinale Sabouraud. Tinea imbricata (Latin: tile-like Tinea)—a fungal disease of human skin, occurring mainly in Brazil, in South India and South China, on the Philippine and Caroline Islands, in New Guinea, and others. The disease is caused by a variety of Trichophyton, first discovered by Manson. The fungus as a rule does not affect hair follicles. The lesion can be localized on the entire body with the exception of the scalp and face; peculiar multiple concentric scaling ring-shaped plaques arise. Treatment is as for superficial trichophytosis of smooth skin (see Trichophytosis). Natives are predominantly affected. Tinea nodosa—a rare lesion of the hair, described by Cheatle and Morris (1879); nodular thickenings form on the hair shaft similar to those in piedra (see Trichosporosis). Unlike trichorrhexis nodosa (see Trichorrhexis), these nodules do not represent a frayed hair, but consist of light-refracting bodies, the true nature of which is unknown.