Synonyms.—Phthiriasis; Morbus Pediculosis; Lousiness.

Definition.—A local or general cutaneous irritation due to the presence of the louse, or pediculus, and is vulgarly known as lousiness.

There are three varieties of this parasite that are found in man, each selecting its own field of operation, and rarely invading any other territory, and that only by accident and is temporary. The pediculus capitis, or head louse, having for its field of operation the region of the scalp. The pediculus corporis, or body louse, has a larger field of operation and is on the general body surface, while the pediculus pubis has for its habitat the pubic region, though it may be found on other parts where the hairs are short and stiff, as the axillae, the eyebrows, the eyelashes, and the stiff hair of the breast.

Pediculus Capitis.—The head louse is much smaller than the body or clothes louse, and is about two mm. long and one mm. broad; head acutely triangular and provided with two hairy antennae, each of five articulations, and two eyes, a narrow thorax, with three hairy legs, provided with tarsal booklets, projecting from each side. The male is much smaller than the female, and is found in smaller numbers.

The ova, or nits, are minute, dirty-white, pear-shaped bodies, glued to the hair by chitinous substance. They hatch out in from six to eight days, and are sexually mature in from twelve to sixteen days. The female lays from fifty to sixty eggs in a week, or, according to Kaposi, a progeny of five thousand can be reared in eight weeks from a single female. According to Crocker, the color, while generally gray, varies according to the color of its host, being gray with blackish margins on Europeans, white on the Esquimaux, black on the Negro, and yellowish-brown on the Chinese.

Etiology.—While they may be found in all ages, they are most common among children, and those who neither wash or comb their hair frequently. They are conveyed from one to another by direct contact with an individual suffering with the parasites, or by using the same hat, brush, or comb.

Symptoms.—In healthy and well-nourished patients, the only marked symptom is the intolerable itching which causes the patient to scratch, not only at the seat of the parasite, but all over the scalp. They. are more abundant in the occipital region where the hair is the thickest, and here may be found excoriations, which, in the poorly nourished and filthy, soon become pustular, producing impetigo contagiosa, or pustular eczema develops. If means are not used to destroy the parasites, and the hair is neglected, this pustular eruption extends to all parts of the scalp.

Diagnosis.—The diagnosis can readily be made by a careful examination of the head and finding the parasite or nits; the latter need not be mistaken for seborrheic scaly particles, if we remember that the latter can be removed by light brushing or shaking, while the former are firmly glued to the shaft of hair, and can not be removed by brushing.

Treatment.—Where the hair is matted or the nits abundant, it is better to have the hair cut short, though not absolutely necessary. The hair and scalp is to be thoroughly saturated with petroleum, (coal oil) and allowed to remain for ten or twelve hours, when the parasites and ova are entirely destroyed. This will be followed by thoroughly washing the head with warm water and soap; any good toilet soap may be used. Should there be impetigo or eczematous pustules, a bland wash or ointment should be used. The hair should be carefully combed with a fine-tooth comb, in order to remove the ova, shells, and parasites.

Pediculus Corporis.—The body louse resembles the anatomical peculiarities of the pediculus capitis, though much larger, and, like the latter, the female is of greater size. When not distended with blood, they are a light-grayish color. The female lays from seventy to eighty eggs, from which the young develop in from four to eight days, and are sexually mature in from twelve to fifteen days.

This parasite inhabits the clothes, the seams being their hiding-place, as well as their breeding-grounds, though sometimes the ova may be found on the lanugo hairs. It thrives better in impoverished subjects, alcoholics, tramps, and the unwashed class. It is found more frequently in adults than in children.

Symptoms.—The subjective symptoms are an intense itching-, burning, and formication that is distressing. As a result the victim scratches, and parallel wheals or lines are quite characteristic On examining the skin, in addition to the traumatism made by the nails, will be found the characteristic mark of the parasite. This is the minute hemorrhagic speck, the result of the bite. It is not sensible to the touch, and must be carefully sought as one of the diagnostic traits.

A favorite location for the parasites is the neck-band of the shirt, and as they wander forth for a meal, the nucha and shoulders suffer most.

Diagnosis.—This will be made by the characteristic symptoms just named—evidence of scratching, hemorrhagic specks, and parallel wheals. A careful search of the seams of the clothes must be instituted for the parasite and ova.

Treatment.—Unless the ova are found upon the lanugo body-hairs, boiling, baking, or ironing the clothes with very hot irons, will destroy the parasites and their ova. A thorough bath with naphthol-sulphur soap, to be followed by the application of a weak carbolic wash, completes the cure.

Pediculus Pubis.—The "crab-louse," or crab, is smaller than either the head or body louse. It is broader and flatter than the other varieties, the head is rounded, and provided with five pointed antennae, and is attached squarely to the body. The abdominal and thoracic portions show no division. The ova, ten to twenty in number, hatch in six to eight days, and the young are sexually mature in two weeks.

Symptoms.—"Clinging to a couple of hairs, it digs deeply into the orifice of a hair follicle," where it produces intense pruritus, attended by excoriations, papules, pustules, and other inflammatory symptoms. While commonly found in the pubic region, in very filthy persons it may also be found upon the eyebrows and eyelashes.

Diagnosis.—The diagnosis is made by the region involved in the itching, the presence of papules, and excoriations, and by finding the parasite and ova, which requires a very careful search, they being so much smaller than the other parasites.

Treatment.—While efficient, the old blue-ointment is unpleasant, and not infrequently is followed by dermatitis in persons of delicate skin. A wash of four grains of corrosive sublimate to an ounce of water, or an application of strong cologne is far more pleasant and equally efficient.

A favorite application of Shoemaker's is the following:

Beta-naphthol 1 dram (4.0).
Cologne-water 4 ounces.

The Eclectic Practice of Medicine, 1907, was written by Rolla L. Thomas, M. S., M. D.