The diagnosis of Pediculus capitis is not difficult to make when the hairs and hairy scalp are carefully examined for nits and living parasites. In better families it is a good plan to point out the corpora delicti to their possessors and to make them aware of the possible sources of infection.
As regards treatment, lotions of sabadill vinegar are recommended; in slighter cases these are quite sufficient. In severe cases cure will not result unless dressings of petroleum, naphthol ointment (5 to 10 per cent.) and balsam of Peru be applied. In the case of plica polonica, the hair must be cut quite short (even in adults) so as to control matting of the hair. To get rid of nits from hair that is not matted, careful combing and washing with strongly alkaline fluids or with hot vinegar is suitable.
Pediculus vestimenti (Clothes Louse).
The clothes louse attacks adults by preference, and with especial frequency old and emaciated persons. It lives in the clothes, but derives its nourishment from the body. At the moment at which the clothes louse inserts its proboscis into the skin the person experiences a slight sting, which, however, at once ceases to hurt. If the body of the louse is sucked full of blood it falls off and the individual has rest from it for a time. A wheal develops around the hæmorrhagic area of the bitten spot and itches severely. The itching goes on until the eruption is scratched all over. This is followed by crust formation. When many parasites are present the itching reflexes become more severe, and the patients scratch themselves considerably and make long marks at those places where the Pediculi have been. The localization of the scratching effects is characteristic, corresponding with folds between portions of clothing (regions between the shoulder-blades, wrist and neck). If the condition lasts for a month, the scratching effects extend over the whole body, and secondary efflorescences become associated with it, such as pustules, ulcers and eczemas. Intermediate between this we find cicatrices and pigmentation, the latter under certain circumstances extending over the whole body. Sulla, Herod, Cardinal Dupet, Philip II, and others are said to have died from louse disease. That even at present many human beings are exposed to the danger of being devoured by lice is a fact that we have had the opportunity of observing on several occasions. Only to record one instance, a man, aged 65, was received into our clinic some time ago in an absolutely neglected condition (he had been staying for some weeks in a stable, lying on a wretched bed). The whole of the surface of his body was covered with countless furuncles, of greater and less size, which had partly become changed into undermined ulcers. Over the ulcers and beneath their undermined edges Pediculi were swarming.
Phthirius inguinalis (Pediculus pubis) (Crab Louse).
The transmission of these parasites generally takes place during coitus, and therefore they especially occur in the pubes. It is possible also that transmission is effected through dirty clothes and bed-linen and privy seats.[1062] Starting from the pubes the animals crawl out over the other parts of the body provided with hairs to the abdominal wall and the thorax (so far as these parts are furnished with thick hair) to the arm-pits, the beard, the eyebrows; not, however, to the hair of the head, or rarely so; among our numerous cases we have never met with an example of the crab louse attacking the hair of the head.
The irritation produced by the crab louse is extraordinarily severe, especially during the night, as the warmth of the bed incites the lice to active sucking. In consequence of the violent scratching indulged in, eczemas are set up at the points attacked, and these often spread to the neighbouring parts not covered with hair.
Of special interest is the onset of maculæ cæruleæ (tâches bleues) in some persons affected with crab lice (people disposed to sweating seem to be peculiarly liable to these). They consist in pale blue patches of various size and shape, varying from that of a hemp-seed to that of a lentil, and again to that of a nail in size and form. These are found over the cutaneous surface of the abdomen, thorax and thigh, and are often only seen by a good lateral illumination. Duguet[1063] considers that the condition is a toxic erythema, that it is set up, on the occasion of the bite of the parasite penetrating the skin, by the poisonous substance derived from it. Oppenheim[1064] considers that it is a colouring substance that is formed in the salivary glands of the parasites, and which penetrates the skin when the insects bite, and thus forms the maculæ cæruleæ. We have on several occasions emulated the experiment of Duguet (trituration in a mortar of crab lice freshly taken from the human body and inoculating the mass thus obtained beneath the skin), and have similarly been enabled to produce the maculæ cæruleæ experimentally, but we have certainly been unable to determine which of the hypotheses is the correct one, the toxic erythema or the colouring substance inhibition theory.
The diagnosis of phthirasis is very easy, for either the sexually mature parasites or the nits are found on the hairs.
As regards treatment, grey ointment is regarded as a generally useful application; it gives rise, however, to a slight eczema of the genitals, especially in males, when injudiciously used. Geber[1065] recommends petroleum or balsam of Peru, Oppenheim[1066] a 1 per cent. sublimate solution for lotions, or a mixture of equal parts of petroleum and benzine when the sublimate cannot be borne. The use of a 5 per cent. ointment with hydrarg. oxid. flavum is worth considering in treatment of pediculosis of the eyebrows and eyelashes. The simplest method of treatment, and one with a radical effect, is that by sulphuric ether recommended by Thomer.[1067] It certainly produces a sharp burning sensation, but the living parasites and nits are destroyed in one sitting. We prefer ether lotions as a rule, and we thoroughly rub the affected parts with a pad of wadding well soaked with the ether. The dead parasites and the nits fall on to what lies beneath when the rubbing is done thoroughly, and the burning sensation caused by the ether only lasts a few minutes.