the latter axis, or 'polar axis of the place, cannot affect the apparent motions of a pendulum suspended at the equator of that axis, which is the great circle through the place of observation. The pendulum will therefore be affected only by a motion round the axis through the place, which is the case first investigated. And the amount of this motion will evidently vary as the sine of the latitude. Hence the time of apparent revolution of the plane of oscillation=a sidereal day x sine of latitude. The gyroscope is an application of the well-known principle of the dynamics of a rigid body, that if a mass be set in rotation freely in space, it will, unless it be disturbed, preserve in all cases its original plane of rotation, and to effect this, will even overcome slight impediIt will be easily seen from fig. 2, and from the description given above of the instrument itself, how the rotation of the earth is hence deduced. It was in September, 1852, that M. Foucault presented to the Academy of Sciences an account of the gyroscope. In this apparatus also there is a fixed plane below which the earth turns, and as it carries with it the spectator, causes it to appear to him as if the plane of the disc actually revolved.

ments.

The disc has the mass composing it disposed as much as possible around its edge, in order that, when put in rotation, it may revolve for a longer time than it otherwise would.

Since all the particles of this rotating disc have a tendency by virtue of centrifugal force to fly off at a tangent to the circumference of the disc, in the plane in which it is vibrating; hence, any attempt to change the direction of this plane in space will be opposed by part of the force with which, were they not restrained by the law of cohesion, each particle of the disc would fly off.

Mr. Wheatstone has described in a paper, read before the Royal Society in April, 1854, a form of the gyroscope, fig. 1, which we will briefly describe, as the experiments performed with it will be very easily transferred to the more perfect form, fig. 3. It is thus conFig. 3.

structed: a beam is capable of moving freely round a horizontal axis, which is itself moveable round a vertical axis, so that the beam may move in any direction round a fixed point; at one end of the beam is fixed a horizontal ring which carries a heavy disc, the axis of rotation of which is in a line with the beam; at the other end is a shifting weight by means of which the equilibrium of the beam may be established or disturbed at pleasure.

If the beam be brought into equilibrium, and the disc be rapidly rotated, as by means of a string quickly unrolled from its axis, the beam will have no tendency to displace itself in any direction. But if we now disturb in any way the equilibrium, moving the weight towards the centre of the beam, and thus causing the disc to preponderate, then, if the disc rotates from right to left, the beam will move round the vertical axis also from right to left, and vice versa. If we cause the equipoise to preponderate, contrary effects will take place.

The velocity of rotation of the beam round the vertical axis increases in proportion to the disturbance of the equilibrium. Notwithstanding too the increased or diminished action of gravity on the disc, its axis of rotation always preserves the same inclination to the vertical axis at which it was originally placed. When the equilibrium is disturbed while the disc is at rest, the beam being placed in any other position than the vertical, gravity acts so as to turn it round a horizontal

ARTS AND SCI. DIV. VOL. IV.

axis; but when the disc is in motion, the usual effect of gravity disappears, and there is substituted for it a continued rotation round a vertical axis, that is, round an axis perpendicular to the plane containing the axes of the two impressed rotations.

A similar composition of forces takes place when the disc is caused to rotate while the equilibrium of the beam is preserved, by impressing on the beam a rotation round a vertical axis. When the disc rotates from right to left, the slightest pressure tending to produce rotation round the vertical axis in the same direction, causes the end of the beam carrying the disc to ascend, and a pressure in the opposite direction causes it to descend, that is, the beam is constrained to move round a horizontal axis perpendicular to the vertical plane containing the two axes of impressed rotation-a case exactly analogous to the preceding. The beam ascends and descends in like manner, after rotation has spontaneously taken place round the vertical axis in consequence of the equilibrium being disturbed, whenever this rotation is in any way accelerated or retarded. As the centre of gravity of the beam is below its point of suspension, even when equipoised, it is in perfect equilibrium only when it is horizontal, consequently, if it be elevated above or depressed below this position, it will endeavour to resume it, tending to produce in the two cases rotation in opposite directions round a horizontal axis; the rotation of the disc combined with this tendency, gives rise, as in the other cases, to continued rotation round a vertical axis; the direction being determined in a similar manner.

In all these experiments the axis of the rotating disc has been supposed to be fixed in the prolongation of the beam; but now let us suppose this axis placed at any inclination and any azimuth with respect to it, it is evident that the inclination of this axis should produce no difference in the character, but merely in the intensity, of the effects, since in any inclined position of the disc its rotation is resolvable into others, one perpendicular to the beam, and the other, which produces no effect, in a plane containing it. When the axis of the rotating disc is vertical and at right angles to the beam, no rotation on the vertical axis ought to take place in any case; but it is found that, although the beam be horizontal and in equilibrium, there is a motion round the vertical axis in opposite directions, according as one or other end of the axis of the disc is uppermost. This motion, however, is evidently due merely to the friction of the pivots dragging the beam to a corresponding motion; because whether it be accelerated or retarded no change is produced in the horizontality of the beam.

To take a few more experimental illustrations: let the system of rings carrying the disc be removed from the rest of the apparatus, and let the inner ring be allowed to move freely within the outer. Having set the disc in rotation, hold the outer ring at the end of the diameter which is in the plane in which the axis of motion of the disc is free to move; then giving to the outer ring a tendency to rotation round that diameter, in whatever position the axis is, it will fly to place itself in the fixed axis thus determined, and rotation will take place round it in the same direction; while considerable resistance is felt so long as the moveable axis is changing its position; but when once it coincides with the fixed axis, the rotation of the external ring is easily effected. So, also, a slight alternate motion of the outer ring, tending to give it rotation in opposite directions, will cause a continued rotation of the moveable axis; and similarly, when we try to rotate the outer ring round an axis perpendicnlar to its plane. In all cases, when the axis of the rotating disc is free to move in a plane, and the outer ring is constrained to rotate round a line in this plane, the moveable axis will place itself so as to coincide with that line, and so that the disc shall rotate in the same direction as the ring; if the fixed axis be in a different plane, the moveable axis will assume permanently that position in its plane which approaches nearest to the former. The moveable axis is thus apparently attracted towards the fixed axis, if the rotations are in the same direction, and repelled from it if they are in opposite directions.

In all these experiments the free and constrained axes of rotation are supposed to intersect, but in Fessel's apparatus they are distant from each other. In this case, the rule must be thus modified, that the free axis of rotation tends to place itself parallel to the constrained axis, or as nearly so as possible. By this principle all the results are easily explained. Thus, when the equilibrium of the beam is destroyed gravity tends to make it rotate round a horizontal axis; the axis of the disc tries to place itself parallel with that axis, but being unchangeably at right angles to it, the tendency to place itself there causes rotation round the vertical axis.

Again, fix the outer ring horizontally, and loosen the inner ring, keeping them, however, both in the same plane; then, on moving the beam round the vertical axis, the axis of the disc will fly to place itself parallel thereto. The rings being placed in the vertical plane, the same result will follow, if the beam be moved in a vertical plane, that is, round a horizontal axis of rotation.

Before describing a few more experiments with the gyroscope, we will again revert to its theoretic action, in order to explain more clearly the phenomena. We quote from a pamphlet, by Mr. Ladd, of Chancery-lane, accompanying his instrument:

"Every particle of a disc revolving on an axis has a tendency to fly therefrom, on account of centrifugal force; but diametrically opposite are the similar particles exerting the same influence on the axis. This 99

H

is an aspirate of the guttural series, and is a faint pronunciation of the sound which in the German alphabet is denoted by ch. In the earliest alphabets, as the Greek and Hebrew, the symbol whence the modern character is derived [ALPHABET] denoted the syllable che or he. Hence the Hebrew name was cheth or heth; and the Greek probably at first heta, as it was afterwards eta. As the guttural sound disappeared in the latter language, the letter finally denoted the simple vowel e. On the other hand, in the Latin alphabet it was retained as the symbol of the aspirate. The English name aitch was probably at first ech, with the vowel prefixed, as in ef, el, &c. The guttural sound of ch is often confounded with the sibilant ch, as heard in church. The letter h is liable to the following changes in different dialects or kindred languages:

1. H is interchangeable with c. This is well seen in a comparison of the Latin and German languages [C, 3]. To the examples there given may be added the Latin decem compared with the German zehen, and ducere compared with ziehen (zug).

2. His interchangeable with ch. Thus the Greek forms xeu-wv, XeiμEpivos, XOPTOS, xauai, are severally connected with the Latin hiems, hibernus, hortus, humi.

3. H with chth. This is similar to the interchange of p with pt, as seen in the Greek nouns TOMIS and TOλis, woλeμos, and TTONEμos. Of the interchange between the aspirates there are examples | in the Greek x@es compared with the Latin root hes-, seen in heri and hesternus, and perhaps the Greek x0ov (nom. x0wv) compared with the Latin humo- (nom. humus).

4. H is interchangeable with g. Examples: the German zehe compared with the Latin digito-: the German fliehen, sehen, compared with the English substantives flight, sight; and perhaps the Latin vehemens, the first element of which is identical with the German prefix weg, a derivation which will make vehemens equivalent to amens or demens.

5. H with 8. Compare the Latin sub, sex, septem, sus, salio, with the Greek ὑπο, ἐξ, ἑπτα, ύς, άλλομαι, &c. Thus the ancient Spanish town Hermandica, mentioned by Livy in his 21st book, is proved by the Greek form Helmantice to be identical with Salmantica, the ancient name of Salamanca.

6. H with f. Hence the Latin words hostis, hostia, says Festus, were sometimes written fostis, fostia. So, too, the French word hors, well known in the phrase hors de combat, is derived from the Latin foris. The Spanish language abounds in examples of this change, as in the names Herdinando and Ferdinando; so also hermoso, from the Latin formoso; the Portuguese retains the form formoso-.

7. H with w. Many Greek words which had originally the digamma (another name for the letter w) at the beginning, took a mere aspirate afterwards. So in our own language the word who has nearly exchanged the w for what is sounded as an h; and the relative adverb how is no doubt derived from the relative itself. It is in this way that the Latin homo (homon-) is uomo in Italian and uhom in Walachian.

8. When any consonant or consonants in the middle of words had nearly lost all sound, the letter h appears to have been employed as a fit representative of the vanishing sound. Hence in German stehen and gehen, for what must originally have been standen and gangen; but the h of the Latin mih-i is part of the stem, as shown by the German forms ich and mich of the same pronoun.

9. The letter h is often dropped altogether in pronunciation, and hence in writing also. This was perhaps the reason why the Greeks gave up the letter h for the little mark called the spiritus asper. In Latin many words are written indifferently, with or without an h, as arena, harena; arundo, harundo; onustus, honustus. Thus the last words show that hon-or and hon-us (onus), honestus and honustus, are all of the same origin, being derived from a root hon, denoting a load or charge, which is either an honor or a burden, according to the nature of The Italians for the most part, like the inhabitants of ancient Rome, are averse to all aspirates; the people of Tuscany, on the other hand, still maintain their ancient character for the strongest pronunciation of these harsh sounds. Evidence of this is seen in the name Leghorn, which no doubt more accurately represents the pronunciation which prevailed on that part of the Italian coast, than Livorno.

the case.

HABEAS CORPORA JURATO'RUM, a judicial writ for the purpose of enforcing the attendance of jurors, abolished by the Common Law Procedure Act, 1852. [JURY.]

HA'BEAS CORPUS is a writ at the common law, used for various purposes. When the writ of Habeas Corpus is spoken of without further explanation, it always implies the important writ which will presently be described; but it is also used for certain formal purposes in the courts of common law at Westminster for removing prisoners from one court into another, and for compelling the attendance of prisoners as witnesses, &c. But the great writ of Habeas Corpus is that which in cases of alleged illegal confinement is directed to the person who detains another; and the purport of the writ is a command to

such person to produce the body of the prisoner, and to state the cause of his detention, and, further, to submit to and receive whatsoever the judge or court awarding the writ shall direct. The old writ de homine replegiando was issued for the purpose of replevying a man out of custody in the same manner as chattels taken in distress may be replevied [REPLEVIN] upon giving security to the sheriff that the man should be forthcoming to answer any charge against him. And if the prisoner was removed out of the sheriff's jurisdiction, the sheriff might make his return accordingly, and thereupon a process issued (called a capias in withernam) to imprison the party withholding the prisoner until he was produced. From the many exceptions, however, with which this writ was guarded, especially in causes where the crown was concerned, it was a very insufficient remedy. The decision of the judges of the King's Bench in the early part of the reign of Charles I., that they could not, upon a Habeas Corpus, bail or deliver a prisoner, though committed without any cause assigned, in cases where he was committed by the special command of the king, or by the lords of the Privy Council, caused the parliamentary inquiry which was followed by the Petition of Right, which recites this judgment, and enacts that no freeman shall be so imprisoned or detained. The court, however, and the judges, still endeavoured to uphold the prerogative of the crown; and, consequently, the statute 16 Car. I. c. 10, was extorted by the parliament, enacting that any person committed by the king himself or his Privy Council, or any members thereof, should have the writ of Habeas Corpus granted to him upon demand or motion made to the court, which should thereupon, within three court days after the return of the writ, examine and determine the legality of the commitment, and do justice in delivering, bailing, or remanding the prisoner. Still, however, new shifts and devices were made use of to prevent the due execution of this act, and eventually the statute 31 Chas. II., c. 2., was passed, which is called the Habeas Corpus Act, and is frequently spoken of as another Magna Charta. By this statute the methods of obtaining this writ are plainly pointed out, and so long as it remains in force no English subject can be long detained in prison, except in those cases where the law justifies a detainer. And lest it should be evaded by demanding unreasonable bail, it is declared by the 1 W. & M., stat. ii., c. 2, that excessive bail shall not be required.

It has been customary in times of alleged danger to suspend the Habeas Corpus Act; but these are in fact the very times when the statute is most necessary. The Habeas Corpus is the protection only of the innocent, not the defence of the guilty. A suspension of the Habeas Corpus Act is effected by an act of parliament authorising the crown, for a limited period, to imprison suspected persons without giving any reason for so doing. But it has been customary to pass acts of indemnity subsequently, for the protection of those who have acted under the suspension. An instance of the one is afforded by the 57 Geo. III. c. 3, and of the other by the 58 Geo. III. c. 6. (Blackst., Comm.,' Mr. Kerr's ed., vol. iii.)

The statute 31 Chas. II. has been re-enacted or adopted, if not in terms yet in substance, in most of the American states. The New York statutes formerly provided for relief under the writ de homine replegiando, in favour of fugitives from service in any other state; but this provision has been held to be contrary to the constitution and laws of the United States, and void in respect to slaves being fugitives from states where slavery is lawful. (Kent's 'Com.')

HABE'RE FA'CIAS POSSESSIO'NEM, a judicial writ directed to the sheriff, commanding him to put the person who has recovered a chattel or possessory interest in lands into actual possession. It corresponds to the Habere facias seisinam; but now that the possession alone is recovered in ejectment, this writ is the one most in use. [EXECUTION.]

HABE'RE FA'CIAS SEISI'NAM, a judicial writ directed to the sheriff, commanding him to put the person who has recovered a freehold interest in lands into actual possession. In the execution of this writ, as well as of the writ of labere facias possessionem, the sheriff may justify breaking open doors if the possession be not quietly delivered. The execution is effected by the delivery of a twig, or a clod, &c., if land; or by the delivery of the key of the door, &c., if a house is the subject matter of which the sheriff is directed to put the recoveror in possession,-all other persons being first removed from the premises. But if it be the presentation to a benefice which is recovered, the execution is by writ de clerico admittendo, directed, not to the sheriff, but to the bishop or archbishop, directing him to admit and institute the clerk of the recoveror. [EXECUTION.] HACKNEY COACH. [STAGE CARRIAGE.] HÆMATE MESIS (from alua, blood, and euéw, to vomit), a bleeding from or into the stomach. [HÆMORRHAGE.] HÆMATO CELE (from alua, blood, and kýλŋ, a tumour), an effusion of blood into the scrotum.

HÆMATO'XYLON CAMPECHIA'NUM (Logwood), a tree native of Campeachy, but cultivated also in both the West and East Indies. The finest wood is the produce of the former place. The bark and alburnum being removed, there is within a dark red coarse-fibred duramen, having a violet-like odour, and a taste at first sweetish, afterwards astringent. It dyes the saliva violet-coloured, and produces a similar change on many of the other secretions. Specific gravity, 1.057. Ten pounds of wood yield 16-18 ounces of extract. Its chief constituents are volatile oil, resinous or fatty matter, a principle termed hæmatoxyline, which is occasionally found in the wood in the form of crystals, and a brown matter containing tannin. Logwood acts as a mild astringent in hemorrhages or increased secretions; and in some forms of diarrhoea it often effects a cure where more powerful astringents fail. (See Abercrombie on Diseases of the Stomach, &c.') It may be exhibited in the form of infusion or of extract: the former is preferable. It is accused of causing phlebitis, or inflammation of the veins, in some cases where it had checked the diarrhoea; but this is very rarely met with. Logwood is also used extensively in the arts, especially for dyeing. It gives the peculiar colour to the paper in which sugar-loaves are generally wrapped. It forms the basis of red ink, when Brazil wood is not used. HÆMATURIA (from alua, blood, and ovpov, urine), voiding of bloody urine. [HÆMORRHAGE; KIDNEYS, DISEASES OF.] HÆMO'PTYSIS (from aiua, blood, and Tów, to spit), a spitting or coughing of blood. [HEMORRHAGE; LUNGS, DISEASES OF; PHTHISIS PULMONALIS.] HÆMORRHAGE (from alua, blood, and phyvvui, to break). The most common cause of hæmorrhage is external violence, by which the vessels of a part are divided, and the blood escapes from their cavities. When an artery of some calibre is wounded, a bright scarlet stream of blood is propelled to a distance proportioned to the size of the vessel, in a current continuous, yet increased in force at intervals corresponding with the pulsations of the heart. This is called a jetting stream. If a vein of some size be divided, a stream of dark crimson blood is projected in a perfectly continuous and equable current, and with less force than from an artery of the same calibre, in consequence of the loss of power which the blood sustains in its passage through the minute capillary vessels. In wounds in which no vessel of more than a line in diameter has been divided, the blood flows in a constant more or less rapid oozing, but is not projected to any distance from the body; and when it issues from both kinds of vessels at once, and in equal quantities, its colour is intermediate between those peculiar to each of them. The same mixture of the two kinds of blood may sometimes, when a number of small vessels of both kinds, and a large one of either kind, are simultaneously divided, make it doubtful, from the colour alone, to which kind it belongs; and the distinction becomes still more difficult if the arterial blood be long detained in the tissues, for then it assumes a venous colour.

When a large artery, as one of the main trunks of the limbs or head, is divided, the blood rushes forth with such impetuosity that life is often destroyed almost instantaneously. The quantity of blood lost however, and the rapidity with which death ensues, will depend in some measure on the freedom of exit which the blood finds after issuing from the wounded vessel, as well as on the mode in which it is wounded. If there be a free external aperture, no obstacle is presented to its flow, and death speedily follows; if, on the contrary, the aperture be small, as in a punctured wound, the blood can escape but slowly, and is liable to coagulate in the passage, so as partially to block it up and render it still more narrow. If again the artery be completely divided, its extremities will retract into the tissues around, and be thus partly covered, so that the hæmorrhage will be retarded. If it be cut longitudinally, the blood will flow much less rapidly than if the wound be transverse, because the aperture will gape much less widely. If, lastly, the wound be not cleanly made, if the edges be rough and torn, as by a gun-shot, no blood at all will flow, at least for some time. None of these circumstances, however, is likely to do more than retard the fatal consequence of a wound of a large artery, unless immediate assistance be given.

When an arterial branch of the second magnitude, as one of the primary divisions of the main trunks in the leg or fore-arm, is wounded, the flow of blood is at first profuse, and a large quantity is soon lost; but after a time the patient faints from extreme exhaustion, and then the heart ceasing to act the blood no longer flows, but begins to coagulate both within and around the vessel, whose extremities contract, and further loss may thus be prevented. More frequently, however, as soon as the patient recovers from his exhaustion, and the heart regains some of its power, the slight obstacles formed during the fainting are forced away, and the hemorrhage recommences and continues till the patient is again exhausted. Thus by a succession of hæmorrhages and of temporary staunchings, he may at last be destroyed by extreme debility. From arteries of smaller size, as those about the fingers, &c., the blood flows at first in a rapid little stream, but after a few minutes, if they are exposed to the cold air, they retract; their orifices contract and close, and the bleeding altogether ceases, without much danger of returning.

Hæmorrhage from wounded veins is of less importance. It is much more slow, for the blood is prevented by the valves from flowing from that part of the vein which is between the heart and the orifice, and in

the part which is beyond the orifice it has only the force of that in the smaller arteries. Hence it is seldom immediately fatal, and when the patient becomes faint the edges of the vessel fall together, instead of remaining open as those of arteries. Thus a coagulum forms within and around them, and, except from the largest trunks, prevents any further flow. Other cases in which bleeding takes place from large vessels are those in which they are burst by sudden efforts, as sometimes happens in the aorta, especially when it or the heart is diseased; those in which the walls of an aneurism or otherwise diseased artery or vein burst or ulcerate; those in which ulceration, whether in internal or external organs, spreads from surrounding parts, and at last (though they always resist for a long time) invades the walls of arteries and veins. The bleeding so common from ulcerated surfaces, and from various vascular morbid growths, probably depends on rupture of the very delicate vessels which they contain; and the same delicacy of the walls of its vessels, with their great liability to disease in advanced life, may be assigned for many cases of hæmorrhage in the more vascular parts of the brain producing apoplexy.

But bleeding to a great extent may take place without visible rupture of any vessel. This form of hæmorrhage, which may take place in various parts of the body, is that popularly supposed to arise from the "bursting of a blood-vessel; " but in the large majority of cases where blood is poured forth in the interior of the body, the most careful examination can discover no aperture through which it had flowed. It is therefore called hæmorrhage by exhalation, from the idea that the vessels which in health are traversed only by the fluids of the exhalations or secretions, now permit the passage of the blood. The only instances in which the blood has been seen flowing in these cases are those extremely rare ones of hæmorrhage from the skin of the face, hands, feet, &c. In these the surface is covered by a dew of blood; if this be wiped away no unnatural appearance is perceptible, but the blood soon exudes again. From this the process would appear to be very similar to that of menstruation. When internal organs from which hemorrhage has taken place are examined after death, they are sometimes found loaded with blood, but at others quite pale, their vessels having been completely emptied; when pressed, small clots of blood like grains of sand sometimes ooze out on the surface, as if proceeding from the orifices of secreting ducts. From these and other circumstances it is probable that the blood does pass through the vessels which naturally are permeated by the secretions, though the minute details of neither process are yet wholly explicable. It cannot however be certainly affirmed that the minute blood-vessels are not ruptured, for neither the apertures nor the cicatrices in them could be in any way visible.

The circumstances under which these hæmorrhages take place are various. In some cases they arise from distension of the vessels in consequence of some local excitement, either with or without increased activity of the circulation generally; and in these the flow of blood is preceded by a sensation of fullness and throbbing in the part, which, if visible, appears red and swollen. Such are those which take place in bronchitis, producing some rare cases of hæmoptysis; in dysentery and acute inflammation of the intestines; from the membrane of the nose, producing the epistaxis so common in young persons in robust health; in the brain, producing some forms of apoplexy, especially those connected with hypertrophy of the heart; and occasionally in the acute inflammations of nearly all the tissues. In other cases the main cause of the hemorrhage is the existence of some obstacle to the free passage of the blood through the vessels. Such are those very frequent cases in which hæmoptysis, or spitting of blood, takes place in consumption, where the blood is obstructed in its passage through the pulmonary arteries by the masses of tuberculous matter deposited around them; those of hæmatemesis, or vomiting of blood, which arise from obstruction of the splenic or portal vein, by coagula, or by disease of the liver or other adjacent organs, and the consequent congestion of the vessels of the stomach; many of those which occur from the stomach, uterus, and other organs, in the early stages of various structural diseases; those which depend on disease of the heart, producing obstruction in the large vessels, and which may take place in the brain, lungs, and various other organs; and those arising from obstacles in the veins, as in hanging, or even from the influence of gravitation.

But a simply mechanical distension of the vessels, whether from an increased afflux of blood into them, or a retarded removal of it from them, cannot explain all the phenomena of these spontaneous hæmorrhages. In many cases a peculiar condition of the vessels, or of the blood itself, must be assumed, and is indeed nearly proved. To these must be referred many cases of what is called idiopathic hæmorrhage, as in some instances of hæmatemesis, hæmaturia, &c. In some persons, indeed, there appears to be a peculiar disposition to bleeding, a hæmorrhage diathesis. Mr. Abernethy (Surgical Lectures') used to speak of a bleeding family, in all of whom it was extremely difficult to staunch the blood from even the slightest wound; and among other similar cases are not a few in which fatal hæmorrhage has followed the extraction of a tooth, or, in children, the application of leeches. Every surgeon, also, must have observed that in the same operations in different persons the number of vessels requiring to be tied varies greatly; in some amputations, for example, it is not necessary to secure more than the main artery, while in others eight or more must be tied, and this not admitting of any explanation from local differences.

Many other circumstances might be adduced to show that there are conditions of the smaller vessels in which they may not only more easily permit hæmorrhages, but are less capable of effecting those changes which are necessary for arresting them, and on these conditions the majority of the hæmorrhages termed passive must be supposed to depend. Such are especially those from the nose, rectum, and other organs, which occur in persons of weak lax habit, and which may be distinguished from the first class we have noticed rather by the general appearance of the patient than by any local circumstances.

Lastly, there are cases in which the hæmorrhages that take place, often coincidently from several organs, may be presumed to depend on alterations of the blood itself. Such are those that occur in scurvy, in which the blood, when drawn from a vein, does not separate, as in health, into a firm coagulum and a clear serum, but settles into a loose, livid, or dark jelly-like mass, and rapidly putrefies. Such, too, are probably the petechial and other effusions of blood in fever. Hæmorrhages by exhalation may take place habitually or constitutionally, without injuring the health; most commonly the blood flows from the nose or rectum, more rarely from the lungs or stomach, or even from the skin. They are sometimes periodical; and when occurring in men, have seemed to favour the idea of a periodic action of the system in the male sex as in the female, and the more so as the menstrual evacuation, when suppressed in the latter, is not unfrequently compensated for by hæmorrhage from some other organ. Most of the cases of spontaneous bleeding from the skin are of this class; and in other instances the blood has flowed at regular periods from the gums, the breasts, umbilicus, axillæ, or kidneys, but most frequently from the stomach or lungs. Similar vicarious hæmorrhages occur in men when an habitual discharge from any organ has been suppressed, or when an old ulcer has been suddenly healed.

Of the means of arresting Hæmorrhages.--When an artery is wounded, unless death rapidly follow, a natural process takes place by which further bleeding may be prevented. If completely divided, both extremities retract into the sheath of cellular tissue in which they lie, so that a considerable interval is produced between them, bounded by loose and irregular walls, into which the blood as it flows infiltrates, and, coagulating, tends to fill it up and obstruct the vessel. The open mouths of the artery also contract, and gradually, but at last completely close, either at or just above their extremities. As the stream of blood is thus checked by the narrowing and closing of its canal, at the same time that, by the faintness induced by the previous loss, the action of the heart is weakened and the whole circulation retarded, it begins to coagulate within the vessel itself, till its tube is nearly filled by a clot adhering loosely to its walls. Further changes then ensue; the divided vessel and the parts around become inflamed; coagulating lymph is effused from the edges of the wound into the artery itself and over its extremities, forming a firmer plug than the blood alone had. In process of time this lymph becomes organised, vessels enter it from the parts around, and it becomes firmly and permanently united to them and the vessel, till at length its tube is rendered impervious from the point of division up to the first branch given off from it, and is at last converted into a solid cord, closely connected with the substance of the cicatrix around it. If the artery be only partially divided, the same effects follow; though, if the cut be extensive transversely, with less certainty, because retraction cannot take place, and the internal coagulum, if formed, is washed away by the stream which still partly passes along the vessel. The natural cessation of hæmorrhages from veins is effected in the same manner, but far more easily; for the valves prevent any bleeding from the part nearest to the heart, and both orifices, instead of gaping open, fall together, and soon become

adherent.

But in the human subject it is only in the very small arteries that the hæmorrhage can be confidently expected to terminate thus naturally, and hence various artificial means of checking bleeding from the larger ones have been invented. The simplest of these is pressure: if the finger be placed with moderate firmness over the mouth of a small bleeding vessel for a minute or two, on removing it the orifice will be found closed, and no more blood will flow. Pressure is also especially useful when a number of small arteries are bleeding together, with a constant oozing rather than a rapid flow of blood: in such cases, when the edges of the wound are brought together, a compress should be laid on, and bandaged firmly and steadily over them. The same means, or a tourniquet applied a short distance above the wound, so as to compress the trunk of the artery, may be useful by lessening the force and volume of the current, and thus permitting the natural processes to take place undisturbed. But if these means be insufficient, the artery must be tied; if it be completely divided, ligatures must be placed on both extremities; and if only partially cut, then on both sides of the opening-for, from the numerous communications of the arteries, when the main current is checked, another in a retrograde direction is always established into the part beyond the ligature. The operation of the ligature is not merely to prevent mechanically the flow of blood from the opened vessel. When a fine cord is drawn tightly round an artery, something is felt to give way under it, and, on removing it and opening the artery, its inner and middle membranous coats are found cleanly cut through as with a knife, while the outer coat remains. When the ligature is left on, it embraces this outer coat

loosely, and thus rendering the canal impervious, completely prevents further bleeding. The blood thus becoming stagnant, coagulates in the lower part of the vessel and adheres to its walls; these at the same time inflame, coagulating lymph is effused from their cut edges, and becoming organised, at last, as in the natural process, completely fills up the canal of the vessel, while the part constricted by the ligature ulcerates and gives way, permitting the cord to be safely drawn away at the end of from six to sixteen days.

Previous to the general use of the ligature, introduced by Ambrose Paré in the 16th century, numberless means for checking hæmorrhages, then so frequently fatal, were resorted to by surgeons, under the names of styptics, astringents, &c. They were in the habit of applying hot irons to the stumps of amputated limbs to stop the bleeding, which it is probable the eschar thus formed would generally effect. At present however the use of the actual cautery is nearly abolished in this country; it can only be justifiable in the few cases where, from peculiarity of situation, the vessel can neither be tied nor compressed, and for such cases it is certainly the most effectual styptic known. Cold air or ice is nearly as useful, and far oftener applicable: it is quite sufficient in all common cases where only small vessels are divided. In the very few cases where any astringents are required, as in some of external bleeding from diseased surfaces or from tumours, the best are solutions of sulphate of copper and of alum. Another class of remedies that may be usefully employed are those which act mechanically-as sponge, agaric, lint, and other light very porous bodies, which placed over a small bleeding orifice will soon completely obstruct it by favouring the coagulation of the blood.

Such are the principal modes of treatment applicable in cases of external or surgical hemorrhage in which vessels are divided by external injury, and are within reach of the eye or fingers. In internal hæmorrhages however it is obvious that mechanical means can rarely be employed. From the varied nature of the cases from which they arise it is evident that different means may be required in the several kinds of cases. In those so closely related to inflammation, in which there is accumulation of blood from local or general excitement, the hæmorrhage is itself a naturally curative means of its cause, and need not be checked unless it implicates some important organ, as the brain, and then the most advisable means of arresting it is to bleed from the arm. So, too, in cases of habitual or vicarious hæmorrhages, if not dangerous or very inconvenient from locality, it will seldom be advisable to check them, for they are generally outlets by which a plethoric condition that would else be highly injurious is cured; at any rate they should be arrested gradually and cautiously. Where external means are applicable none are so useful as cold, or, as a last resource, pressure; as by plugs put in the nostrils, &c. Where a mechanical obstacle to the passage of the blood exists, medicine can often do nothing for the permanent cure of the hemorrhage that it produces. For the time, the most effectual means are cool air, cold water or ice applied as near as convenient to the seat of bleeding, iced drinks, perfect quietude, and the avoidance of all stimuli; the body should be placed in that position in which blood may gravitate from the affected part, and if there be any indication of plethora or accelerated circulation blood should be drawn from the arm to an amount to be determined by the circumstances of the case. In many cases great benefit results from exciting the vessels, of and near the part, to a copious secretion of the usual fluids, as in some cases of hæmatemesis by administering purgatives. If astringent remedies be deemed advisable, and in many cases they are highly useful, the acetate of lead will generally be preferable, and next to it the different vegetable compounds of gallic acid. [ASTRINGENTS.] The treatment of the peculiar class of hæmorrhages from alteration of the blood is considered under FEVER, &c. Bleeding from the nose is treated under EPISTAXIS. (J. F. D. Jones, On Hamorrhage and the Ligature; T. Watson, Cyclopædia of Medicine, art. Hæmorrhage.') HÆMORRHOIDS (from alua blood, and pèw, to flow), varicose tumours of the veins of the rectum. [ANUS, DISEASES OF THE.] HÆRETICO COMBURENDO, WRIT DE. [HERESY.] HAGUE, ALLIANCE OF THE. [TREATIES, CHRONOLOGICAL TABLE OF.]

HAIL, HAILSTONES, HAILSTORMS. The conversion of the aqueous vapour which is an essential constituent of the atmosphere, by the depression of its temperature, either successively into water and ice, or immediately into the latter without the sensible intervention of the former state; and whether in the atmosphere itself, or on the ground, or against the surfaces of bodies resting upon it or extended into the air, presents several subjects for philosophical investigation, all of them having important relations to the welfare of man and of the various beings of organic nature he associates around him, as well as to the operations of human life. Water in the solid state is produced from the atmosphere in several ways, and in different forms. portion of the vapour in the air at certain elevations freezes, by the sudden reduction in temperature of its entire mass, it becomes converted into innumerable separate congeries of minute perfect crystals of ice, which are called flakes of snow; when that in contact with solid bodies forming part of the surface of the earth, or immersed in the atmosphere, becomes sufficiently lowered in temperature by their loss of heat by radiation, hoar-frost appears; and under other physical

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