The universe, the abode of man, harbors all forms of animal and vegetable life. Some exist for his benefit, others await an opportunity to invade and live within the human structure. To the latter the term “parasite” has been applied. There are two varieties of parasites, those belonging to the vegetable kingdom and known as vegetable parasites, or fungi, and those of the animal kingdom, termed animal parasites.
This chapter will be devoted to the study of those common skin diseases caused by vegetable and animal parasites.
THE SKIN DISEASES CAUSED BY VEGETABLE PARASITES
The vegetable parasites are living bodies because they require nourishment and reproduce. Most of them are rather hardy, for they can grow in materials of but little nutritional value. These parasites consist essentially of tiny round or oval masses of living matter, surrounded by a double wall, and visible only with the aid of the microscope. These masses are termed “spores.” When these spores are heaped up, one on top of the other, they form into hollow, tubelike structures with crossbars at various distances. These are technically termed mycelial threads. These threads produce branches in the same manner as a tree. Some of the parasites can be grown outside of the body upon special nutritional materials termed culture media, and this is one way by which scientists are able to differentiate one variety of parasite from another.
The more common skin conditions caused by vegetable parasites include ringworm (tinea trichophytina), favus (tinea favosa), and liver-spot disease (tinea versicolor).
Ringworm.Varieties.Ringworm is the most frequent of the diseases of the skin caused by vegetable parasites. Many different parts of the smooth skin surface may be invaded, especially that of the face, neck, and backs of the hands; the groin and the adjoining surfaces; and the webs of the fingers and toes. The hairy skin surfaces affected are the scalp and the bearded areas. The nails but rarely suffer. Detailed description of only the most frequent forms of ringworm will be given.