An excess or defect in the quantity of the fluids is scarcely an object of this part of our work, yet to consider the doctrine of plethora in this place may facilitate some future enquiries. These sources of disease are the and of pathologists, and are, on the whole, the distinguishing marks of youth and old age. Each, as may be supposed, is relative to different temperaments, and even idiosyncracies; each may be apparently in excess, and each may predispose to disease, though still within the limits of health. The consequences of the excess of either of the component parts of the blood may be easily understood from the former observations on lentor or tenuity. We now mean to speak only of the excess of the whole mass, which is styled plethora. This is divided into the ple-thora ad molem; plethora ad spatium; plethora ad volume?!, and plethora ad vires; nor is the distinction frivolous: it were better that it had been more attended to by modern authors.

The plethora ad molem, ad vasa, or ad venas, for they are synonymous in ancient authors, is the exuberance of the absolute quantity of blood, and, in more delicate habits, is seen by the fulness and redness of the minute vessels. In scrophulous habits, however, this redness docs not always denote plethora; nor do they easily bear large evacuations, much less astringents, which are often ignorantly prescribed on account of a fancied weakness. In more robust habits this kind of plethora is chiefly discovered by a full, oppressed, or rather a laboured pulse, and sometimes by a fulness of the veins. In general it occurs in strong robust constitutions, where the digestive powers are vigorous, and the waste from exercise disproportioned to the supply.

The plethora ad spatium is produced when the quantity of circulating fluids remaining the same, the capacity of the vessels is contracted. This happens in cold weather, and in the cold fits of fevers, when in weak habits haemorrhages are not uncommon. It happens also more frequently than is suspected, by the rash imprudent use of astringents, particularly in full mobile habits, in persons of a languid circulation, or in cases of haemoptoe.

Plethora ad volumen usually implies an increased bulk of the blood from external heat, from violent inflammatory fevers, from friction, from violent passions, spirituous liquors, etc. The blood, however, is not capable of any very considerable expansion, and these appearances of plethora arise from relaxation in consequence of external warmth, or a determination to the surface, from a more accelerated circulation.

The plethora ad vires, though it exist, is still less an object of our present consideration, as it means only a greater quantity of blood than the strength will bear. This, of course, must be relative to the constitution of the patient; but we may add, that it is a more frequent source of disease than is suspected, and peculiarly difficult to relieve, as we have often had occasion to remark, since the slightest diminution of the circulating fluids produces fainlness. >

It will be obvious that these different plethoras are not inconsistent with each other, and that all may be occasionally combined. The disease such an union may produce will be of course more dangerous, and sudden death has often been the consequence.

The deficiency of blood the is supposed to arise from copious evacuations, or from famine. Faint-ness, however, arises in the former instance before a considerable portion can be lost, and in the latter the contraction of the vessels accommodates them to the quantity. In the infant, however, who dies from not tying the umbilical cord, wc have remarked (see Me-dicina Forensis) that the vessels are unusually empty, and Lieutaud, as well as Morgagni, has recorded instances of the vessels being peculiarly empty, though without connecting this appearance with the previous symptoms; an omission too common in each. It is sufficient therefore to point out the existence of such a state, since from want of such information we cannot enlarge on its source or its consequences.

Mohbi solidi simplicis. This subject fills a large space in the foreign systems of pathology, and were it not from respect to the talents of men like Boerhaave, Gaubius, De Haen, and Ludwig, wc should pass it over very slightly. It will not, however, detain us long, though we shall add in part to their views.

The diseases which can affect the simple solid are those which relate to its cohesion or its chemical nature. The state of cohesion, the only objects of the Bocrhaavian school, must be relative in different organs, in different ages, sexes, temperaments, and constitutions. In general, the cohesion of the various organs must be in the natural proportion of each. If too slight to bear the requisite motions, it constitutes disease; or indeed if it require very peculiar caution to avoid injury from such motions, it is equally a disease, though in a less degree.

Weakness, or diminished cohesion, in a solid when not ruptured, is divided into, 1st, the lax and flaceid in soft parts which admit of distention by a moderate force; 2dly, the inert, or inelastic, in parts naturally elastic; 3dly, the flexible, as in bones which admit of being bent, after being previously softened.

When rupture has taken place in the tender fibres of soft parts, it is styled tenerum gracile: when accompanied with general softness, as from putrefaction, tabi-dum. It is called fissile when parts, naturally soft, are dry and chapped; and fragile when hard parts are broken in consequence of their weakness.

Rigidity, an opposite disease, consists in increased cohesion, and is styled tenax when in soft parts, as the muscles of old animals; durum, when in the harder parts, as cartilages proceeding to ossification; and fragile vilreum when in the bones.