The following are the principal forms of the several elementary lesions of the skin:

Maculae, or Stains, are simply spots of around or irregular form, not elevated above the surface of the skin. They may be due to deposits of blood or the coloring matter of the blood, to fungus growth, or to deposits of bile pigment.

Redness or Hypercemia - Due to distention of the arteries or veins When arterial in character, the difficulty disappears upon pressure with the finger. It may be accompanied by violent itching and rising of temperature; is frequently followed by peeling off of the scarf skin. It may be occasioned by local irritation, by changes in the blood, or by nervous excitement.

Wheels consist of reddish swellings with pale centers, which form rapidly and disappear as suddenly. The nettle sting is a perfect illustration of the wheel. They are accompanied by heat and severe tingling. Wheels are characteristic of nettle-rash.

Papula, or pimples, are small hard or raised formations in the. skin.

Vesicles are little sacs in the skin, containing serous fluid or sweat.

Blebs, or bullae:, are simply large vesicles.

Pustules are small, round vesicles containing pus.

Squamae, or scales, are detached portions of the thin scarfskin or epithelial scales.

Tubercles are little solid elevations of the skin, larger than papules.

Nodules are solid masses, larger than tubercles and smaller than cherries. Masses larger than cherries are called tumors.

Scabs or crusts are dry, hard masses of pus and dead skin.

Excoriation is a removal of the epidermis, exposing, but not injuring, the outer skin.

Ulceration is an excavation made in the skin by disease. It usually leaves a sear upon healing.

Fissure is a crack in the skin, such as occurs on the knuckles when the hands are chapped.

A Cicatrix, or scar, is a growth of hard fibrous tissue, occupying the place of the healthy tissue, which has been removed by injury or disease. Some diseases of the skin exhibit only one form of eruption, while in others, a number of elementary lesions occur, either at the same time, or in successive stages of the disease. In some cases, also, two or more different diseases of the skin occur at the same time.