that part, which were accustomed to run before by the ulcer. Hence it appears, that feveral of the Capfula of the hair are deftroyed, and confequently that the patient after the cure has a bald head.

CHA P. II.

Of the PHTHIRIASIS, or MORBUS PEDICULARIS.

THOUGH this fubject is very nauseous and disagreeable to the physician, yet he should not be ignorant thereof, nor neglect its treatment, being very troublesome, and even dangerous, to children. It may happen to all, but it is more frequently observable in dirty, neglected infants. Some authors report, that they have seen infinite numbers of lice on all parts of the body; that they not only appeared on its furface, but also betwixt the cuticula and cutis, forming whitish fuperficial tumours. This kind of Pthiriafis I never obferved: but have frequently feen it in the head, especially of those who are infected with a scabies, tinea, or crufta lactea, of that part.

The

The better to underftand the nature of these vermin, we shall diftinguish them into three fpecies, viz. thofe of the head, those of the trunck, and those of the parts of generation. Though the Greeks have given them no, particular names nor defcriptions, yet it is certain, that they are of three diftinct fpecies, and are different by their figure, nature, and feat. I can atteft, from several observations made by the help of microscopes, that the vermin of the trunck differ in nature, figure, and feat, from both the other fpecies, as the vertuofi alfo affirm.

eggs

The origin of Pediculi the moderns juftly derive from eggs; for the axiom, omne animal ex ovo, is true in this cafe. These in the head are small, round, and whitish tumours or vehicles, fixed to the roots of the hair. This vermin have diftinct males and females, and are not hermophrodites, as feveral authors have imagined. The males have four tefticles. This discovery we chiefly owe to Lewenhoek, who from his experiments thereon, merits to be read on this fubject. Valifneri, who wrote in particular of infects, has made a great many experiments

periments on the fame fubject. They both evince, that the generation of these vermin, as well as that of all imperfect animals, is infinitely numerous; for they have computed, that one male and female loufe, fomented betwixt the cutis and fcarf-fkin, in two months time, engender'd ten thousand more, which Lewenhoek in particular has also attefted; and the ancients, with fome moderns, were of opinion, that the generation of these as well as of other animals, was owing to pu-trefaction: but repeated experience and reafoning have demonftrated the contrary.

Before we proceed any farther to this theory, it will be neceffary to answer the following queftions, 1. Whence fpring the vermin of the head, particularly in such as have had none before? 2. Why fome are more fubject to them than others, whilst their femina may be equally in both? 3. Why the vermin of the head in fome children, fo obftinately refifts the force of all remedies, fo that they seem to be eradicable?

As to the first queftion, this vermin very probably fpring from a dirty unclean nurse,

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as well thofe of the head, as the reft beforementioned: for they never appear, if they be not communicated by a loufy infected perfon, to one that is not..

II. Some are much more fubject to them than others, through their particular difpofitions, inasmuch as they foment better the pedicular femina, as we fee that fome feeds grow better in certain lands, than they do in others, and that every country has its particular products, according to the nature of the climate and foil; all which is applicable to the generation of these vermin rather in fome perfons than in others. The most probable difpofition obfervations could as yet fuggeft, is a thick infipid humour, with a dirty uncombed head, &c. Hence we fee, that children of a cold phlegmatic conftitution, full of a milky thick humour, are much more subject to vermin, than those of a thin, bilious, and hot constitution, whofe humours are thin and acrid; for which reasons, adults are not fo frequently troubled with these vermin, as children who have that quality in their blood, particularly fuch as have the crufta lactea, tinea, or Scabies of the head.

III. This

III. This fpecies of vermin is with difficulty deftroyed, as often as they are plentifully fed and protected from the action of the remedies employed for their destruction. This is frequent in the crufta lactea, tinea, and fcabies, efpecially when the fcab has not fallen; for the vermin then work them

felves under it, and feed upon the purulent, or rather milky humour which flows from the affected part, where they are infinitely multiplied in spight of all remedies.

A fingular fact, but no lefs true than any of the former, prefents itself here: its detail is fomewhat long: I have frequently obferved it. This is a pouch, or kind of veficular tumour, or large knob, without any orifice or other iffue, full of vermin, which swim in a fmall quantity of purulent fanies, moftly obfervable on the head of fome children. But how is this formed? I own it favours pretty much the opinion of thofe, who held that vermin are engender'd in the very body, without any foreign semina; feeing we can perceive no paffage whereby they may enter externally. But we fhall find this fyftem ill-grounded, if we confider, that this vermin have a very fine sharp