In the United States of America, express companies for the rapid

transmission of parcels and luggage and light goods generally perform

the function of the post office or the railways in the United Kingdom

and the continent of Europe. Not only do they deliver goods, but by the

cash on delivery system (see CASH) the express companies act as agents

both for the purchaser and seller of goods. They also serve as a most

efficient agency for the transmission of money, the express money order

being much more easily convertible than the postal money orders, as the

latter can only be redeemed at offices in large and important towns. The

system dates back to 1839, when one William Frederick Harnden

(1813-1845), a conductor on the Boston and Worcester railway, undertook

on his own account the carrying of small parcels and the performance of

small commissions. Obliged to leave the company's service or abandon his

enterprise, he started an "express" service between Boston and New York,

carrying parcels, executing commissions and collecting drafts and bills.

Alvin Adams followed in 1840, also between Boston and New York. From

1840 to 1845 the system was adopted by many others between the more

important towns throughout the States. The attempt to carry letters

also was stopped by the government as interfering with the post office.

In 1854 began the amalgamation of many of the companies. Thus under the

name of the Adams Express Company the services started by Harnden and

Adams were consolidated. The lines connecting the west and east by

Albany, Buffalo and the lakes were consolidated in the American Express

Company, under the direction of William G. Fargo (q.v.), Henry Wells and

Johnston Livingston, while another company, Wells, Fargo & Co., operated

on the Pacific coast. The celebrated "Pony Express" was started in 1860

between San Francisco and St Joseph, Missouri, the time scheduled being

eight days. The service was carried on by relays of horses, with

stations 25 m. apart. The charge made for the service was $2.50 per 1/2

oz. The completion of the Pacific Telegraph Company line in 1861 was

followed by the discontinuance of the regular service.

The name "express" is applied to a rifle having high velocity, flat

trajectory and long fixed-sight ranges; and an "express-bullet" is a

light bullet with a heavy charge of powder used in such a rifle (see

RIFLE).

EXPROPRIATION, the taking away or depriving of property (Late Lat.

_expropriare_, to take away, _proprium_, i.e. that which is one's own).

The term is particularly applied to the compulsory acquisition of

private property by the state or other public authority.

EXPULSION (Lat. _expulsio_, from _expellere_), the act of driving out,

or of removing a person from the membership of a body or the holding of

an office, or of depriving him of the right of attending a meeting, &c.

In the United Kingdom the House of Commons can by resolution expel a

member. Such resolution cannot be questioned by any court of law. But

expulsion is only resorted to in cases where members are guilty of

offences rendering them unfit for a seat in the House, such as being in

open rebellion, being guilty of forgery, perjury, fraud or breach of

trust, misappropriation of public money, corruption, conduct unbecoming

the character of an officer and a gentleman, &c. It is customary to

order the member, if absent, to attend in his place, before an order is

made for his expulsion (see May, _Parliamentary Practice_, 1906, p. 56

seq.). Municipal corporations or other local government bodies have no

express power to expel a member, except in such cases where the law

declares the member to have vacated his seat, or where power is given by

statute to declare the member's seat vacant. In the cases of officers

and servants of the crown, tenure varies with the nature of the office.

Some officials hold their offices _ad vitam aut culpam or dum bene se

gesserunt_, others can be dismissed at any time and without reason

assigned and without compensation. In the case of membership of a

voluntary association (club, &c.) the right of expulsion depends upon

the rules, and must be exercised in good faith. Courts of justice have

jurisdiction to prevent the improper expulsion of the member of a

voluntary association where that member has a right of property in the

association. In the case of meetings, where the meeting is one of a

public body, any person not a member of the body is entitled to be

present only on sufferance, and may be expelled on a resolution of the

body. In the case of ordinary public meetings those who convene the

meeting stand in the position of licensors to those attending and may

revoke the licence and expel any person who creates disorder or makes

himself otherwise objectionable.

_Expulsion of Aliens._--Under the Naturalization Act of 1870, the last

of the civil disqualifications affecting aliens in England was removed.

The political disqualifications which remained only applied to electoral

rights. In the very exceptional cases in which it was retained in the

statute book, expulsion was considered to have fallen into desuetude,

but it has been revived by the Aliens Act of 1905 (5 Edw. VII. c. 13).

Under this act powers are given to the secretary of state to make an

order requiring an alien to leave the United Kingdom within a time fixed

by the order and thereafter to remain outside the United Kingdom,

subject to certain conditions, provided it is certified to him that the

alien has been convicted of any felony or misdemeanour or other offence

for which the court has power to impose imprisonment without the option

of a fine, &c., or that he has been sentenced in a foreign country with

which there is an extradition treaty, for a crime not being an offence

of a political character. There are also provisions applicable within

one year, after the alien has entered the United Kingdom in the case of

pauper aliens. Precautions are taken to prevent, as far as possible, any

abuse of the power of expulsion. Under the French law of expulsion

(December 3, 1849) there are no such precautions, the minister of the

interior having an absolute discretion to order any foreigner as a

measure of public policy to leave French territory and in fact to have

him taken immediately to the frontier.

EXTENSION (Lat. _ex_, out; _tendere_, to stretch), in general, the

action of straining or stretching out. It is usually employed

metaphorically (cf. the phrase an "extension of time," a period allowed

in excess of what has been agreed upon). It is used as a technical term

in logic to describe the total number of objects to which a given term

may be applied; thus the meaning of the term "King" in "extension" means

the kings of England, Italy, Spain, &c. (cf. DENOTATION), while in

"intension" it means the attributes which taken together make up the

idea of kinghood (see CONNOTATION). In psychology the literal sense of

extension is retained, i.e. "spread-outness." The perception of space by

the senses of sight and touch, as opposed to semi-spatial perceptions by

smell and hearing, is that of "continuous expanse composed of positions

separated and connected by distances" (Stout); to this the term

"extension" is applied. The perception of separate objects involves

position and distance, but these taken together are not extension, which

necessarily implies continuity. To move one's finger along the keys of a

piano gives both the position and the distance of the keys; to move it

along the frame gives the idea of extension. By expanding this idea we

obtain the conception of all space as an extended whole. To this

perception are necessary both form and material. It should be observed

the actual quality of a stimulus (rough, smooth, dry, &c.) has nothing

to do with the spatial perception as such, which is concerned purely

with what is known as "local signature." The elementary undifferentiated

sensation excited by the stimuli exerted by a continuous whole is known

as its "extensive quantity" or "extensity." The term has to do not with

the kind of object which excites the sensation, but simply with the

vague massiveness of the latter. As such it is distinguishable in

thought from extension, though it is not easy to say whether and if so

how far the quantitative aspect of space can exist apart from spatial

order. Extensity as an element in the complex of extension must be

carefully distinguished from intensity. Mere increase of pressure

implies increase of intensity of sensation; to increase the extensity

the _area_, so to speak, of the exciting stimulus must be increased.

Thus the extensity (also called "voluminousness," or "massiveness") of

the sensation produced by a roll of thunder is greater than that

produced by a whistle or the bark of a dog. It should be observed that

this application of the idea of extensity to sensation in general,

rather than to the matter which is the exciting stimulus, is only an

analogy, an attempt to explain a common psychic phenomenon by

terminology which is intrinsically suitable to the physical. As a

natural consequence the term represents different shades of meaning in

different treatises, verging sometimes towards the physical, sometimes

towards the psychic, meaning.

In connexion with extension elaborate psycho-physical experiments have

been devised,.e.g. with the object of comparing the accuracy of tactual

and visual perception and discovering what are the least differences

which each can observe. At a distance two lights appear as one, just as

two stars distinguishable through a telescope are one to the naked eye

(see VISION): again if the points of a compass are brought close

together and pressed lightly on the skin the sensation, though vague and

diffused, is a single one.

See PSYCHOLOGY and works there quoted; also SPACE AND TIME.

EXTENUATING CIRCUMSTANCES. This expression is used in law with reference

to crimes, to describe cases in which, though an offence has been

committed without legal justification or excuse, its gravity, from the

point of view of punishment or moral opprobrium, is mitigated or reduced

by reason of the facts leading up to or attending the commission of the

offence. According to English procedure, the jury has no power to

determine the punishment to be awarded for an offence. The sentence,

with certain exceptions in capital cases, is within the sole discretion

of the judge, subject to the statutory prescriptions as to the kind and

maximum of punishment. It is common practice for juries to add to their

verdict, guilty or not guilty, a rider recommending the accused to mercy

on the ground of grave provocation received, or other circumstances

which in their view should mitigate the penalty. This form of rider is

often added on a verdict of guilty of wilful murder, a crime as to which

the judge has no discretion as to punishment, but the recommendation is

sent to the Home Office for consideration in advising as to exercise of

the prerogative of mercy. Quite independently of any recommendation by

the jury, the judge is entitled to take into account matters proved

during the trial, or laid before him after verdict, as a guide to him in

determining the quantum of punishment.

Under the French law (_Code d'instruction criminelle_, art. 345), it is

the sole right and the duty of a jury in a criminal case to pronounce

whether or not the commission of the offence was attended by extenuating

circumstances (_circonstances attenuantes_). They are not bound to say

anything about the matter, but the whole or the majority may qualify the

verdict by finding extenuation, and if they do, the powers of the court

to impose the maximum punishment are taken away and the sentence to be

pronounced is reduced in accordance with the scale laid down in art. 463

of the _Code penal_. The most important result of this rule is to enable

a jury to prevent the infliction of capital punishment for murder. In

cases of what is termed "crime passionel," French juries, when they do

not acquit, almost invariably find extenuation; and a like verdict has

become common even in the case of cold-blooded and sordid murders, owing

to objections to capital punishment.

EXTERRITORIALITY, a term of international law, used to denominate

certain immunities from the application of the rule that every person is

subject for all acts done within the boundaries of a state to its local

laws. It is also employed to describe the quasi-extraterritorial

position, to borrow the phrase of Grotius, of the dwelling-place of an

accredited diplomatic agent, and of the public ships of one state while

in the waters of another. Latterly its sense has been extended to all

cases in which states refrain from enforcing their laws within their

territorial jurisdiction. The cases recognized by the law of nations

relate to: (1) the persons and belongings of foreign sovereigns, whether

incognito or not; (2) the persons and belongings of ambassadors,

ministers plenipotentiary, and other accredited diplomatic agents and

their suites (but not consuls, except in some non-Christian countries,

in which they sometimes have a diplomatic character); (3) public ships

in foreign waters. Exterritoriality has also been granted by treaty to

the subjects and citizens of contracting Christian states resident

within the territory of certain non-Christian states. Lastly, it is held

that when armies or regiments are allowed by a foreign state to cross

its territory, they necessarily have exterritorial rights. "The ground

upon which the immunity of sovereign rulers from process in our courts,"

said Mr Justice Wills in the case of _Mighell_ v. _Sultan of Johore_,

1804, "is recognized by our law, is that it would be absolutely

inconsistent with the status of an independent sovereign that he should

be subject to the process of a foreign tribunal," unless he deliberately

submits to its jurisdiction. It has, however, been held where the

foreign sovereign was also a British subject (_Duke of Brunswick_ v.

_King of Hanover_, 1844), that he is amenable to the jurisdiction of the

English Courts in respect of transactions done by him in his capacity as

a subject. A "foreign sovereign" may be taken to include the president

of a republic, and even a potentate whose independence is not complete.

Thus in the case, cited above, of _Mighell_ v. _Sultan of Johore_, the

sultan was ascertained to have abandoned all right to contract with

foreign states, and to have placed his territory under British

protection. The court held that he was, nevertheless, a foreign

sovereign in so far as immunity from British jurisdiction was concerned.

The immunity of a foreign diplomatic agent, as the direct representative

of a foreign sovereign (or state), is based on the same grounds as that

of the sovereign authority itself. The international practice in the

case of Great Britain was confirmed by an act of parliament of the reign

of Queen Anne, which is still in force. The preamble to this act states

that "turbulent and disorderly persons in a most outrageous manner had

insulted the person of the then ambassador of his Czarish Majesty,

emperor of Great Russia," by arresting and detaining him in custody for

several hours, "in contempt to the protection granted by Her Majesty,

contrary to the law of nations, and in prejudice of the rights and

privileges which ambassadors and other public ministers, authorized and

received as such, have at all times been thereby possessed of, and ought

to be kept sacred and inviolable." This preamble has been repeatedly

held by our courts to be declaratory of the English common law. The act

provides that all suits, writs, processes, against any accredited

ambassador or public minister or his domestic servant, and all

proceedings and judgments had thereupon, are "utterly null and void,"

and that any person violating these provisions shall be punished for a

breach of the public peace. Thus a foreign diplomatic agent cannot, like

the sovereign he represents, waive his immunity by submitting to the

British jurisdiction. The diplomatic immunity necessarily covers the

residence of the diplomatic agent, which some writers describe as

assimilated to territory of the state represented by the agent; but

there is no consideration which can justify any extension of the

immunity beyond the needs of the diplomatic mission resident within it.

It is different with public ships in foreign waters. In their case the

exterritoriality attaches to the vessel. Beyond its bulwarks captain and

crew are subject to the ordinary jurisdiction of the state upon whose

territory they happen to be. By a foreign public ship is now understood

any ship in the service of a foreign state. It was even held in the case

of the "Parlement Belge" (1880), a packet belonging to the Belgian

government, that the character of the vessel as a public ship was not

affected by its carrying passengers and merchandise for hire. In a more

recent case an action brought by the owners of a Greek vessel against a

vessel belonging to the state of Rumania was dismissed, though the

agents of the Rumanian government had entered an appearance

unconditionally and had obtained the release of the vessel on bail, on

the ground that the Rumanian government had not authorized acceptance of

the British jurisdiction (The "Jassy," 1906, 75 L.J.P. 93).

Writers frequently describe the exterritoriality of both embassies and

ships as absolute. There is, however, this difference, that the

exterritoriality of the latter not being, like that of embassies, a

derived one, there seems to be no ground for limitation of it. It was,

nevertheless, laid down by the arbitrators in the "Alabama" case

(Cockburn dissenting), that the privilege of exterritoriality accorded

to vessels had not been admitted into the law of nations as an absolute

right, but solely as a proceeding founded on the principle of courtesy

and mutual deference between different nations, and that it could

therefore "never be appealed to for the protection of acts done in

violation of neutrality."

The exterritorial settlements in the Far East, the privileges of

Christians under the arrangements made with the Ottoman Porte, and other

exceptions from local jurisdictions, are subject to the conditions laid

down in the treaties by which they have been created. There are also

cases in which British communities have grown up in barbarous countries

without the consent of any local authority. All these are regulated by

orders in council, issued now in virtue of the Foreign Jurisdiction Act

1890, an act enabling the crown to exercise any jurisdiction it may have

"within a foreign country" in as ample a manner as if it had been

acquired "by cession or conquest of territory." A very exceptional case

of exterritoriality is that granted to the pope under a special Italian

enactment. (T. Ba.)

EXTORTION (Lat. _extorsio_, from _extorquere_, to twist out, to take

away by force), in English law the term applied to the exaction by

public officers of money or money's worth not due at all, or in excess

of what is due, or before it is due. Such exaction, unless made in good

faith (i.e. in honest mistake as to the sum properly payable), is a

misdemeanour by the common law and is punishable by fine and (or)

imprisonment. Besides the punishment above stated, an action for twice

the value of the thing extorted lies against officers of the king (1275,

3 Edw. I. c. 26). There are numerous provisions for the punishment of

particular officers who make illegal exactions or take illegal fees:

e.g. sheriffs and their officers (Sheriffs Act 1887), county court

bailiffs (County Courts Act 1888), clerks of courts of justice, and

gaolers who exact fees from prisoners. A gaoler is also punishable for

detaining the corpse of a prisoner as security for debt. The term

"public officer" is not limited to offices under the crown; and there

are old precedents of criminal proceedings for extortion against

churchwardens, and against millers and ferrymen who demand tolls in

excess of what is customary under their franchise.

The term extortion is also applied to the exaction of money or money's

worth by menaces of personal violence or by threats to accuse of crime

or to publish defamatory matter about another person. These offences

fall partly under the head of robbery and partly under blackmail, or

what in French is termed _chantage_.

See _Russell on Crimes_ (6th ed., vol. i. p. 423; vol. iii. p. 348).

EXTRACT (from Lat. _extrahere_, to draw out), in pharmacy, the name

given to preparations formed by evaporating or concentrating solutions

of active principles; _tinctures_ are solutions which have not been

subjected to any evaporation. "Liquid extracts" are those of a syrupy

consistency, and are generally prepared by treating the drug with the

solvent (water, alcohol, &c.) and concentrating the solution until it

attains the desired consistency. "Ordinary extracts" are thick,

tenacious and sometimes even dry preparations; they are obtained by

evaporating solutions as obtained above, or the juices expressed from

the plants.

Extraction, in chemical technology, is a process for separating one

substance from another by taking advantage of the varying solubility of

the components in some chosen solvent. The term "lixiviation" is used

when water is the solvent. In laboratory practice all the common

solvents are employed. With small quantities it may suffice to shake the

substance with the solvent, the mixture being heated if necessary,

filter and distil or otherwise remove the solvent from the distillate.

For larger quantities continuous extraction is advisable. This may be

carried out in many forms of apparatus; one of the most convenient is

the Soxhlet extractor, in which the extract siphons into the flask

containing the solvent, and so maintains the quantity of available

solvent practically constant. Continuous extraction is generally the

practice in technology. One of the most important applications is in the

fat and gelatine industries.

EXTRADITION (Lat. _ex_, out, and _traditio_, handing over), the

surrender of an alleged criminal for trial by a foreign state where he

has taken refuge, to the state against which the alleged offence has

been committed. When a person who has committed an offence in one

country escapes to another, what is the duty of the latter with regard

to him? Should the country of refuge try him in its own courts according

to its own laws, or deliver him up to the country whose laws he has

broken? To the general question international law gives no certain

answer. Some jurists, Grotius among them, incline to hold that a state

is bound to give up fugitive criminals, but the majority appear to deny

the obligation as a matter of right, and prefer to put it on the ground

of comity. And the universal practice of nations is to surrender

criminals only in consequence of some special treaty with the country

which demands them.

There are two practical difficulties about extradition which have

probably prevented the growth of any uniform rule on the subject. One is

the variation in the definitions of crime adopted by different

countries. The second is the possibility of the process of extradition

being employed to get hold of a person who is wanted by his country, not

really for a criminal, but for a political offence. In modern states,

and more particularly in England, offences of a political character have

always been carefully excluded from the operation of the law of

extradition.

1. UNITED KINGDOM.--The Extradition Acts 1870-1873 (33 & 34 Vict. cc.

62, and 36 & 37 Vict. c. 60) and the Fugitive Offenders Act 1881 (44 &

45 Vict. c. 69) deal with different branches of the same subject, the

recovery and surrender of fugitive criminals. The Extradition Acts apply

in the case of countries with which Great Britain has extradition

treaties. The Fugitive Offenders Act applies--(1) as between the United

Kingdom and any British possession, (2) as between any two British

possessions, and (3) as between the United Kingdom or a British

possession and certain foreign countries, such as Turkey and China, in

which the crown exercises foreign jurisdiction.

_Conditions of Surrender._--In spite of some earlier authorities it has

long been settled that in English law there is no power to surrender

fugitive criminals to a foreign country without express statutory

authority. Such authority is now given by the Extradition Acts

1870-1873, but only in the case of the offences therein specified, and

with regard to countries with which an arrangement has been entered

into, and to which the acts have been applied by order in council. The

acts are further to be applied, subject to such "conditions, exceptions

and qualifications as may be deemed expedient" (s. 2); and these

conditions, &c., are invariably to be found in the extradition treaty

which is set out in the order in council applying the Extradition Acts

to a particular country. To support a demand for extradition from Great

Britain it is therefore necessary to show that the offence is one of

those enumerated in the Extradition Acts, and also in the particular

treaty, and that the acts charged amount to the offence according to the

laws both of Great Britain and of the state demanding the surrender.

_Surrender of Subjects._--A further question arises where a state is

called on to surrender one of its own subjects. Some of the treaties,

such as those with France and Germany, stipulate that neither

contracting party shall surrender its own subjects, and in such cases a

British subject cannot be surrendered by his own country. The treaties

with Spain, Switzerland and Luxemburg provide for the surrender by Great

Britain of her own subjects, but there is no reciprocity. Other

treaties, such as those with Austria, Belgium, Russia and the

Netherlands, give each party the option of surrendering or refusing to

surrender its own subjects in each particular case. Under such treaties

British subjects are surrendered unless the secretary of state

intervenes to forbid it. Lastly, some treaties, such as that with the

United States, contain no restriction of this kind, and the subjects of

each power are freely surrendered to the other. Surrender by Great

Britain is also subject to the following restrictions contained in s. 3

of the Extradition Act 1870:--(1) that the offence is not of a political

character, and the requisition has not been made with a view to try and

punish for an offence of a political character; (2) that the prisoner

shall not be liable to be tried for any but the specified extradition

offences; (3) that he shall not be surrendered until he has been tried

and served his sentence for offences committed in Great Britain; and (4)

that he shall not be actually given up until fifteen days after his

committal for extradition, so as to allow of an application to the

courts.

_Political Offences._--The question as to what constitutes a political

offence is one of some nicety. It was discussed in _In re Castioni_

(1890, 1 Q.B. 149), where it was held, following the opinion of Mr

Justice Stephen in his _History of the Criminal Law_, that to give an

offence a political character it must be "incidental to and form part of

political disturbances." Extradition was accordingly refused for

homicide committed in the course of an armed rising against the

constituted authorities. In the more recent case of _In re Meunier_

(1894, 2 Q.B. 415), an Anarchist was charged with causing two explosions

in Paris--one at the Cafe Very resulting in the death of two persons,

and the other at certain barracks. It was not contended that the outrage

at the cafe was a political crime, but it was argued that the explosion

at the barracks came within the description. The court, however, held

that to constitute a political offence there must be two or more parties

in the state, each seeking to impose a government of its own choice on

the other, which was not the case with regard to Anarchist crimes. The

party of anarchy was the enemy of all governments, and its effects were

directed primarily against the general body of citizens. The test

applied in the earlier case is perhaps the more satisfactory of the two.

With regard to the provision that surrender shall not be granted if the

requisition has in fact been made with a view to try and punish for an

offence of a political character, it, was decided in the case of _Arton_

(1896, 1 Q.B. 108) that a mere suggestion, that after his surrender for

a non-political crime, the prisoner would be interrogated on political

matters (his alleged complicity in the Panama scandal), and punished for

his refusal to answer, was not enough to bring him within the provision.

The court also held that it had no jurisdiction to entertain a

suggestion that the request of the French government for his extradition

was not made in good faith and in the interests of justice.

_Extradition Offences._--The following is a list of crimes in respect of

which extradition may be provided for under the Extradition Acts

1870-1873, and the Slave Trade Act 1873. _Extradition Act_ 1870:--(1)

Murder; (2) Attempt to murder; (3) Conspiracy to murder; (4)

Manslaughter; (5) Counterfeiting and altering money, uttering

counterfeit or altered money; (6) Forgery, counterfeiting, and altering

and uttering what is forged or counterfeited or altered; (7)

Embezzlement and larceny; (8) Obtaining money or goods by false

pretences; (9) Crimes by bankrupts against bankruptcy law; (10) Fraud by

a bailee, banker, agent, factor, trustee or director, or member or

public officer of any company made criminal by any law for the time

being in force; (11) Rape; (12) Abduction; (13) Child-stealing; (14)

Burglary and housebreaking; (15) Arson; (16) Robbery with violence; (17)

Threats by letter or otherwise with intent to extort; (18) Crimes

committed at sea: (a) Piracy by the law of nations; (b) Sinking or

destroying a vessel at sea, or attempting or conspiring to do so; (c)

Assault on a ship on the high seas, with intent to destroy life or to do

grievous bodily harm; (d) Revolt, or conspiring to revolt, by two or

more persons on board a ship on the high seas against the authority of

the master; (19) Bribery. _Extradition Act_ 1873:-(20) Kidnapping and

false imprisonment; (21) Perjury and subornation of perjury. This act

also extends to indictable offences under 24 & 25 Vict. cc. 96, 97, 98,

99, 100, and amending and substituted acts. Among such offences included

in various extradition treaties are the following:--(22) Obtaining

valuable securities by false pretences; (23) Receiving any money,

valuable security or other property, knowing the same to have been

stolen or unlawfully obtained; (24) Falsification of accounts (see _In

re Arton_, 1896, 1 Q.B. 509); (25) Malicious injury to property, if such

offence be indictable;. (26) Knowingly making, without lawful authority,

any instrument, tool or engine adapted and intended for the

counterfeiting of coin of the realm; (27) Abandoning children; exposing

or unlawfully detaining them; (28) Any malicious act done with intent to

endanger the safety of any person in a railway train; (29) Wounding or

inflicting grievous bodily harm; (30) Assault occasioning actual bodily

harm; (31) Assaulting a magistrate or peace or public officer; (32)

Indecent assault; (33) Unlawful carnal knowledge, or any attempt to have

unlawful carnal knowledge, of a girl under age; (34) Bigamy; (35)

Administering drugs or using instruments with intent to procure the

miscarriage of women; (36) Any indictable offence under the laws for the

time being in force in relation to bankruptcy. _Slave Trade Act_ 1873

(36 & 37 Vict. c. 88, s. 27):--(37) Dealing in slaves in such manner as

to constitute a criminal offence against the laws of both states.

The United Kingdom has extradition treaties with practically all

civilized foreign countries; and though it is not practicable to state

which of the statutory extradition offences are included in each, it may

be said generally that crimes 1 to 17 inclusive are covered in all,

though Rumania has reserved the right to refuse, and Portugal does

refuse, to surrender for a crime punishable with death.

The act of 1873 provides for the surrender of accessories before and

after the fact to extradition crimes, and most of the treaties contain a

clause by which extradition is to be granted for participation in any of

the crimes specified in the treaty, provided that such participation is

punishable by the laws of both countries. Several of the treaties also

contain clauses, providing for optional surrender in respect of any

crime not expressly mentioned for which extradition can be granted by

the laws of both countries.

It is further to be noted that the restrictions on surrender in the

Extradition Acts apply only to surrenders by Great Britain. Foreign

countries may surrender fugitives to Great Britain without any treaty,

if they are willing to do so and their law allows of it, and such

surrenders have not infrequently been made. But when surrendered for an

extradition crime, the prisoner cannot be tried in England for any other

crime committed before such surrender, until he has been restored, or

has had an opportunity of returning, to the foreign state from which he

was extradited.

_Procedure._--To obtain from a foreign country the extradition of a

fugitive from the United Kingdom, it is necessary to procure a warrant

for his arrest, and to send it, or a certified copy, to the home

secretary together with such further evidence as is required by the

treaty with the country in question. In most, cases an information or

deposition containing evidence which would justify a committal for trial

in Great Britain will be required. The home secretary will then

communicate through the foreign secretary and the proper diplomatic

channels with the foreign authorities, and in case of urgency will ask

them by telegraph for a provisional arrest. For the arrest in the United

Kingdom of fugitive criminals whose extradition is requested by a

foreign state, two procedures are provided in ss. 7 and 8 of the act of

1870:--(1) On a diplomatic requisition supported by the warrant of

arrest and documentary evidence, the home secretary, if he thinks the

crime is not of a political character, will order the chief magistrate

at Bow Street to proceed; and such magistrate will then issue a warrant

of arrest on such evidence as would be required if the offence had been

committed in the United Kingdom. (2) More summarily, any magistrate or

justice of the peace may issue a provisional warrant of arrest on

evidence which would support such a warrant if the crime had been

committed within his jurisdiction. In practice a sworn information is

required, but this may be based on a telegram from the foreign

authorities. The magistrate or justice must then report the issue of the

warrant to the home secretary, who may cancel it and discharge the

prisoner. When arrested on the provisional warrant, the prisoner will be

brought up before a magistrate and remanded to Bow Street, and will then

be further remanded until the magistrate at Bow Street is notified that

a formal requisition for surrender has been made; and unless such

requisition is made in reasonable time the prisoner is entitled to be

discharged. The examination of the prisoner prior to his committal for

extradition ordinarily takes place at Bow Street. The magistrate is

required to hear evidence that the alleged offence is of a political

character or is not an extradition crime. If satisfied in these

respects, and if the foreign warrant of arrest is duly authenticated,

and evidence is given which according to English law would justify a

committal for trial, if the prisoner has not yet been tried, or would

prove a conviction if he has already been convicted, the magistrate will

commit him for extradition. Under the Extradition Act, 1895 the home

secretary, if of opinion that removal to Bow Street would be dangerous

to the prisoner's life, or prejudicial to his health, may order the case

to be taken by a magistrate at the place where the prisoner was

apprehended, or then is, and the magistrate may order the prisoner to

be detained in such place. After committal for extradition, every

prisoner has fifteen days in which to apply for _habeas corpus_, and

after such period, or at the close of the _habeas corpus_ proceedings if

they are unsuccessful, the home secretary issues his warrant for

surrender, and the prisoner is handed over to the officers of the

foreign government.

The Extradition Acts apply to the British colonies, the governor being

substituted for the secretary of state. Their operation may, however, be

suspended by order in council, as in the case of Canada, where the

colony has passed an Extradition Act of its own (see Statutory Rules and

Orders).

_Fugitive Offenders Act._--There are no extradition treaties with

certain countries in which the crown exercises foreign jurisdiction,

such as Cyprus, Turkey, Egypt, China, Japan, Corea, Zanzibar, Morocco,

Siam, Persia, Somali, &c. In these countries the Fugitive Offenders Act

1881 (44 & 45 Vict. c. 69) has been applied, pursuant to s. 36 of that

statute, and the measures for obtaining surrender of a fugitive criminal

are the same as in a British colony. The act, however, only applies to

persons over whom the crown has jurisdiction in these territories, and

generally is expressly restricted to British subjects.

Under this act a fugitive from one part of the king's dominions to

another, or to a country where the crown exercises foreign jurisdiction,

may be brought back by a procedure analogous to extradition, but

applicable only to treason, piracy and offences punishable with twelve

months' imprisonment with hard labour or more. The original warrant of

arrest must be endorsed by one of several authorities where the

offenders happen to be,--in practice by the home secretary in the United

Kingdom and by the governor in a colony. Pending the arrival of the

original warrant a provisional arrest may be made, as under the

Extradition Acts. The fugitive must then be brought up for examination

before a local magistrate, who, if the endorsed warrant is duly

authenticated, and evidence is produced "which, according to the law

administered by the magistrate, raises a strong or probable presumption

that the offender committed the offence, and that the act applies to

it," may commit him for return. An interval of fifteen days is allowed

for _habeas corpus_ proceedings, and (s. 10) the court has a large

discretion to discharge the prisoner, or impose terms, if it thinks the

case frivolous, or that the return would be unjust or oppressive, or too

severe a punishment. The next step is for the home secretary in the

United Kingdom, and the governor in a colony, to issue a warrant for the

return of the prisoner. He must be removed within a month, in the

absence of reasonable cause to the contrary. If not prosecuted within

six months after arrival, or if acquitted, he is entitled to be sent

back free of cost.

In the case of fugitive offenders from one part of the United Kingdom to

another, it is enough to get the warrant of arrest backed by a

magistrate having jurisdiction in that part of the United Kingdom where

the offender happens to be. A warrant issued by a metropolitan police

magistrate may be executed, without backing, by a metropolitan police

officer anywhere, and there are certain other exceptions, but as a rule

a warrant cannot be executed without being backed by a local magistrate.

(J. E. P. W.)

2. UNITED STATES.--Foreign extradition is purely an affair of the United

States, and not for the individual states themselves. Upon a demand upon

the United States for extradition, there is a preliminary examination

before a commissioner or judge before there can be a surrender to the

foreign government (Revised Statutes, Title LXVI.; 22 Statutes at Large,

215). It is enough to show probable guilt (_Ornelas_ v. _Ruiz_, 161

United States Reports, 502). An extradition treaty covers crimes

previously committed. If a Power, with which the United States have such

a treaty, surrenders a fugitive charged with a crime not included in the

treaty, he may be tried in the United States for such crime. Inter-state

extradition is regulated by act of Congress under the Constitution of

the United States (Article IV. s. 2; United States Revised Statutes, s.

5278). A surrender may be demanded of one properly charged with an act

which constitutes a crime under the laws of the demanding state,

although it be no crime in the other state. A party improperly

surrendered may be released by writ of _habeas corpus_, either from a

state or United States court (_Robb_ v. _Conolly_, 111 U.S. Reports,

624). On his return to the state from which he fled, he is subject to

prosecution for any crime, though on a foreign extradition the law is

otherwise (_Lascelles_ v. _Georgia_, 148 U.S. Reports, 537).

(S. E. B.).

See Sir E. Clarke, _Treatise upon the Law of Extradition_ (4th ed.,

1904); Biron and Chalmers, _Law and Practice of Extradition_ (1903).

EXTRADOS (_extra_, outside, Fr. _dos_, back), the architectural term for

the outer boundary of the voussoirs of an arch (q.v.).

EXTREME UNCTION, a sacrament of the Roman Catholic Church. In James v.

14 it is ordained that, if any believer is sick, he shall call for the

elders of the church; and they shall pray over him, anointing him with

oil in the name of the Lord; and the prayer of faith shall save him that

is sick, and the Lord shall raise him up; and if he have committed sins,

it shall be forgiven him.

Origen reprobated medical art on the ground that the prescription here

cited is enough; modern faith-healers and Peculiar People have followed

in his wake. The Catholic Church has more wisely left physicians in

possession, and elevated the anointing of the sick into a sacrament to

be used only in cases of mortal sickness, and even then not to the

exclusion of the healing art.

It has been general since the 9th century. The council of Florence A.D.

1439 thus defined it:--

"The fifth sacrament is extreme unction. Its matter is olive oil,

blessed by a bishop. It shall not be given except to a sick person

whose death is apprehended. He shall be anointed in the following

places: the eyes, ears, nostrils, mouth, hands, feet, reins. The form

of the sacrament, is this: Through this anointing of thee and through

its most pious mercy, be forgiven all thy sins of sight, &c. ... and

so in respect of the other organs. A priest can administer this

sacrament. But its effect is to make whole the mind, and, so far as it

is expedient, the body as well."

This sacrament supplements that of penance (viz. remission of

post-baptismal sin) in the sense that any guilt unconfessed or left over

after normal penances imposed by confessors is purged thereby. It was

discussed in the 12th century whether this sacrament is indelible like

baptism, or whether it can be repeated; and the latter view, that of

Peter Lombard, prevailed.

It was a popular opinion in the middle ages that extreme unction

extinguishes all ties and links with this world, so that he who has

received it must, if he recovers, renounce the eating of flesh and

matrimonial relations. A few peasants of Lombardy still believe that one

who has received extreme unction ought to be left to die, and that sick

people may be starved to death through the withholding of food on

superstitious grounds. Such opinions, combated by bishops and councils,

were due to the influence of the _consolamentum_ of the Cathars (q.v.).

In both sacraments the death-bed baptism of an earlier age seems to

survive, and they both fulfil a deep-seated need of the human spirit.

Some Gnostics sprinkled the heads of the dying with oil and water to

render them invisible to the powers of darkness; but in the East

generally, where the need to compete with the Cathar sacrament of

_Consolatio_ was less acutely felt, extreme unction is unknown. The

Latinizing Armenians adopted it from Rome in the crusading epoch. At an

earlier date, however, it was usual to anoint the dead.

In the Roman Church the bishop blesses the oil of the sick used in

extreme unctions on Holy Thursday at the Chrismal Mass,[1] using the

following prayer of the sacramentaries of Gelasius and Hadrian:--

"Send forth, we pray Thee, O Lord, Thy holy spirit, the Paraclete from

Heaven, into this fatness of oil, which Thou hast deigned to produce

from the green wood for refreshment of mind and body; and through Thy

holy benediction may it be for all that anoint, taste, touch, a

protection of mind and body, of soul and spirit, unto the easing away

of all pain, all weakness, all sickness of mind and body; wherefore

Thou hast anointed priest, kings and prophets and martyrs with thy

chrism, perfected by Thee, O Lord, blessed and abiding in our bowels

in the name of our Lord Jesus Christ."

See L. Duchesne, _Origines du Culte Chretien_ (Paris, 1898).

(F. C. C.)

FOOTNOTE:

[1] The oil left over from the year before is burnt.

EYBESCHUTZ, JONATHAN (1690-1764), German rabbi, was from 1750 rabbi in

Altona. He was a man of erudition, but he owed his fame chiefly to his

personality. Few men of the period so profoundly impressed their mark on

Jewish life. He became specially notorious because of a curious

controversy that arose concerning the amulets which Eybeschutz was

suspected of issuing. These amulets recognized the Messianic claims of

Sabbatai Sebi (q.v.), and a famous rabbinic contemporary of Eybeschutz,

Jacob Emden, boldly accused him of heresy. The controversy was a

momentous incident in the Jewish life of the period, and though there is

insufficient evidence against Eybeschutz, Emden may be credited with

having crushed the lingering belief in Sabbatai current even in some

orthodox circles. (I. A.)

EYCK, VAN, the name of a family of Flemish painters in whose works the

rise and mature development of art in western Flanders are represented.

Though bred in the valley of the Meuse, they finally established their

professional domicile in Ghent and in Bruges; and there, by skill and

inventive genius, they changed the traditional habits of the earlier

schools, remodelled the primitive forms of Flemish design, and

introduced a complete revolution into the technical methods of execution

familiar to their countrymen.

1. HUBERT (Huybrecht) VAN EYCK (? 1366-1426) was the oldest and most

remarkable of this race of artists. The date of his birth and the

records of his progress are lost amidst the ruins of the earlier

civilization of the valley of the Meuse. He was born about 1366, at

Maeseyck, under the shelter or protection of a Benedictine convent, in

which art and letters had been cultivated from the beginning of the 8th

century. But after a long series of wars--when the country became

insecure, and the schools which had flourished in the towns decayed--he

wandered to Flanders, and there for the first time gained a name. As

court painter to the hereditary prince of Burgundy, and as client to one

of the richest of the Ghent patricians, Hubert is celebrated. Here, in

middle age, between 1410 and 1420, he signalized himself as the inventor

of a new method of painting. Here he lived in the pay of Philip of

Charolais till 1421. Here he painted pictures for the corporation, whose

chief magistrates honoured him with a state visit in 1424. His principal

masterpiece, the "Worship of the Lamb," commissioned by Jodocus Vijdts,

lord of Pamele, is the noblest creation of the Flemish school, a piece

of which we possess all the parts dispersed from St Bavon in Ghent to

the galleries of Brussels and Berlin,--one upon which Hubert laboured

till he died, leaving it to be completed by his brother. Almost unique

as an illustration of contemporary feeling for Christian art, this great

composition can only be matched by the "Fount of Salvation," in the

museum of Madrid. It represents, on numerous panels, Christ on the

judgment seat, with the Virgin and St John the Baptist at His sides,

hearing the songs of the angels, and contemplated by Adam and Eve, and,

beneath him, the Lamb shedding His blood in the presence of angels,

apostles, prophets, martyrs, knights and hermits. On the outer sides of

the panels are the Virgin and the angel annunciate, the sibyls and

prophets who foretold the coming of the Lord, and the donors in prayer

at the feet of the Baptist and Evangelist. After this great work was

finished it was placed, in 1432, on an altar in St Bavon of Ghent, with

an inscription on the framework describing Hubert as "maior quo nemo

repertus," and setting forth, in colours as imperishable as the picture

itself, that Hubert began and John afterwards brought it to perfection.

John van Eyck certainly wished to guard against an error which

ill-informed posterity showed itself but too prone to foster, the error

that he alone had composed and carried out an altarpiece executed

jointly by Hubert and himself. His contemporaries may be credited with

full knowledge of the truth in this respect, and the facts were equally

well known to the duke of Burgundy or the chiefs of the corporation of

Bruges, who visited the painter's house in state in 1432, and the

members of the chamber of rhetoric at Ghent, who reproduced the Agnus

Dei as a _tableau vivant_ in 1456. Yet a later generation of Flemings

forgot the claims of Hubert, and gave the honours that were his due to

his brother John exclusively.

The solemn grandeur of church art in the 15th century never found, out

of Italy, a nobler exponent than Hubert van Eyck. His representation of

Christ as the judge, between the Virgin and St John, affords a fine

display of realistic truth, combined with pure drawing and gorgeous

colour, and a happy union of earnestness and simplicity with the deepest

religious feeling. In contrast with earlier productions of the Flemish

school, it shows a singular depth of tone and great richness of detail.

Finished with surprising skill, it is executed with the new oil medium,

of which Hubert shared the invention with his brother, but of which no

rival artists at the time possessed the secret,--a medium which consists

of subtle mixtures of oil and varnish applied to the moistening of

pigments after a fashion, only kept secret for a time from gildsmen of

neighbouring cities, but unrevealed to the Italians till near the close

of the 15th century. When Hubert died on the 18th of September 1426 he

was buried in the chapel on the altar of which his masterpiece was

placed. According to a tradition as old as the 16th century, his arm was

preserved as a relic in a casket above the portal of St Bavon of Ghent.

During a life of much apparent activity and surprising successes he

taught the elements of his art to his brother John, who survived him.

2. JOHN (Jan) VAN EYCK (? 1385-1440). The date of his birth is not more

accurately known than that of his elder brother, but he was born much

later than Hubert, who took charge of him and made him his "disciple."

Under this tuition John learnt to draw and paint, and mastered the

properties of colours from Pliny. Later on, Hubert admitted him into

partnership, and both were made court painters to Philip of Charolais.

After the breaking up of the prince's household in 1421, John became his

own master, left the workshop of Hubert, and took an engagement as

painter to John of Bavaria, at that time resident at the Hague as count

of Holland. From the Hague he returned in 1424 to take service with

Philip, now duke of Burgundy, at a salary of 100 livres per annum, and

from that time till his death John van Eyck remained the faithful

servant of his prince, who never treated him otherwise than graciously.

He was frequently employed in missions of trust; and following the

fortunes of a chief who was always in the saddle, he appears for a time

to have been in ceaseless motion, receiving extra pay for secret

services at Leiden, drawing his salary at Bruges, yet settled in a fixed

abode at Lille. In 1428 he joined the embassy sent by Philip the Good to

Lisbon to beg the hand of Isabella of Portugal. His portrait of the

bride fixed the duke's choice. After his return he settled finally at

Bruges, where he married, and his wife bore him a daughter, known in

after years as a nun in the convent of Maeseyck. At the christening of

this child the duke was sponsor, and this was but one, of many

distinctions by which Philip the Good rewarded his painter's merits.

Numerous altarpieces and portraits now give proof of van Eyck's

extensive practice. As finished works of art and models of conscientious

labour they are all worthy of the name they bear, though not of equal

excellence, none being better than those which were completed about

1432. Of an earlier period, a "Consecration of Thomas a Becket" has been

preserved, and may now be seen at Chatsworth, bearing the date of 1421;

no doubt this picture would give a fair representation of van Eyck's

talents at the moment when he started as an independent master, but that

time and accidents of omission and commission have altered its state to

such an extent that no conclusive opinion can be formed respecting it.

The panels of the "Worship of the Lamb" were completed nine years later.

They show that John van Eyck was quite able to work in the spirit of his

brother. He had not only the lines of Hubert's compositions to guide

him, he had also those parts to look at and to study which Hubert had

finished. He continued the work with almost as much vigour as his

master. His own experience had been increased by travel, and he had seen

the finest varieties of landscape in Portugal and the Spanish provinces.

This enabled him to transfer to his pictures the charming scenery of

lands more sunny than those of Flanders, and this he did with accuracy

and not without poetic feeling. We may ascribe much of the success which

attended his efforts to complete the altarpiece of Ghent to the

cleverness with which he [reproduced the varied aspect of changing

scenery, reminiscent here of the orange groves of Cintra, there of the

bluffs and crags of his native valley. In all these backgrounds, though

we miss the scientific rules of perspective with which the van Eycks

were not familiar, we find such delicate perceptions of gradations in

tone, such atmosphere, yet such minuteness and perfection of finish,

that our admiration never flags. Nor is the colour less brilliant or the

touch less firm than in Hubert's panels. John only differs from his

brother in being less masculine and less sternly religious. He excels in

two splendid likenesses of Jodocus Vijdts and his wife Catherine

Burluuts. The same vigorous style and coloured key of harmony

characterizes the small "Virgin and Child" of 1432 at Ince, and the

"Madonna," probably of the same date, at the Louvre, executed for

Rollin, chancellor of Burgundy. Contemporary with these, the male

portraits in the National Gallery, and the "Man with the Pinks," in the

Berlin Museum (1432-1434), show no relaxation of power; but later

creations display no further progress, unless we accept as progress a

more searching delicacy of finish, counterbalanced by an excessive

softness of rounding in flesh contours. An unfaltering minuteness of

hand and great tenderness of treatment may be found, combined with

angularity of drapery and some awkwardness of attitude in the full

length portrait couple (John Arnolfini and his wife) at the National

Gallery (1434), in which a rare insight into the detail of animal nature

is revealed in a study of a terrier dog. A "Madonna with Saints," at

Dresden, equally soft and minute, charms us by the mastery with which an

architectural background is put in. The bold and energetic striving of

earlier days, the strong bright tone, are not equalled by the soft

blending and tender tints of the later ones. Sometimes a crude ruddiness

in flesh strikes us as a growing defect, an instance of which is the

picture in the museum of Bruges, in which Canon van der Paelen is

represented kneeling before the Virgin under the protection of St George

(1434). From first to last van Eyck retains his ability in portraiture.

Fine specimens are the two male likenesses in the gallery of Vienna

(1436), and a female, the master's wife, in the gallery of Bruges

(1439). His death in 1440/41 at Bruges is authentically recorded. He was

buried in St Donat. Like many great artists he formed but few pupils.

Hubert's disciple, Jodocus of Ghent, hardly does honour to his master's

teaching, and only acquires importance after he has thrown off some of

the peculiarities of Flemish teaching. Petrus Cristus, who was taught by

John, remains immeasurably behind him in everything that relates to art.

But if the personal influence of the van Eycks was small, that of their

works was immense, and it is not too much to say that their example,

taken in conjunction with that of van der Weyden, determined the current

and practice of painting throughout the whole of Europe north of the

Alps for nearly a century.

See also Waagen, _Hubert and Johann van Eyck_ (1822); Voll, _Werke des

Jan van Eyck_ (1900); L. Kammerer on the two families in Knackfuss's

_Kunstler-Monographien_ (1898). (J. A. C.)

EYE, a market-town and municipal borough in the Eye parliamentary

division of Suffolk; England; 94-1/2 m. N.E. from London by the Great

Eastern railway, the terminus of a branch from the Ipswich-Norwich line.

Pop. (1901) 2004. The church of St Peter and St Paul is mainly of

Perpendicular flint work, with Early English portions and a fine

Perpendicular rood screen. It was formerly attached to a Benedictine

priory. Slight fragments of a Norman castle crown a mound of probably

earlier construction. There are a town hall, corn exchange, and grammar

school founded in 1566. Brewing is the chief industry. The town is

governed by a mayor, 4 aldermen and 12 councillors. Area, 4410 acres.

Eye (_Heya_, _Aye_) was once surrounded by a stream, from which it is

said to have derived its name. Leland says it was situated in a marsh

and had formerly been accessible by river vessels from Cromer, though

the river was then only navigable to Burston, 12 m. from Eye. From the

discovery of numerous bones and Roman urns and coins it has been thought

that the place was once the cemetery of a Roman camp. William I. gave

the lordship of Eye to Robert Malet, a Norman, who built a castle and a

Benedictine monastery which was at first subordinate to the abbey of

Bernay in Normandy. Eye is a borough by prescription. In 1205 King John

granted to the townsmen a charter freeing them from various tolls and

customs and from the jurisdiction of the shire and hundred courts. Later

charters were granted by Elizabeth in 1558 and 1574, by James I. in

1604, and by William III. in 1697. In 1574 the borough was newly

incorporated under two bailiffs, ten chief and twenty-four inferior

burgesses, and an annual fair on Whit-Monday and a market on Saturday

were granted. Two members were returned to each parliament from 1571

till 1832, when the Reform Act reduced the membership to one. By the

Redistribution Act of 1885 the representation was merged in the Eye

division of the county. The making of pillow-lace was formerly carried

on extensively, but practically ceased with the introduction of

machinery.

EYE (O. Eng. _eage_, Ger. _Auge_); derived from an Indo-European root

also seen in Lat. _oc-ulus_, the organ of vision (q.v.).

ANATOMY.--The eye consists of the eyeball, which is the true organ of

sight, as well as of certain muscles which move it, and of the lachrymal

apparatus which keeps the front of it in a moist condition. The

_eyeball_ is contained in the front of the orbit and is a sphere of

about an inch (24 mm.) in diameter. From the front of this a segment of

a lesser sphere projects slightly and forms the _cornea_ (fig. 1, co).

There are three coats to the eyeball, an external (protective), a middle

(vascular), and an internal (sensory). There are also three refracting

media, the aqueous humour, the lens and the vitreous humour or body.

[Illustration: FIG. 1.--Diagrammatic Section through the Eyeball.

cj, Conjunctiva. L, Lens.

co, Cornea. V, Vitreous body.

Sc, Sclerotic. Z, Zonule of Zinn, the ciliary

ch, Choroid. process being removed to

pc, Ciliary processes. show it.

mc, Ciliary muscle. p, Canal of Petit.

O, Optic nerve. m, Yellow spot.

R, Retina The dotted line behind the

I, Iris. cornea represents its posterior

aq, Anterior chamber of epithelium.]

aqueous humour.

The protective coat consists of the _sclerotic_ in the posterior

five-sixths and the cornea in the anterior sixth. The sclerotic (fig. 1,

Sc) is a firm fibrous coat, forming the "white of the eye," which

posteriorly is pierced by the optic nerve and blends with the sheath of

that nerve, while anteriorly it is continued into the cornea at the

_corneo-scleral junction_. At this point a small canal, known as the

_canal of Schlemm_, runs round the margin of the cornea in the substance

of the sclerotic (see fig. 1). Between the sclerotic and the subjacent

choroid coat is a lymph space traversed by some loose pigmented

connective tissue,--the _lamina fusca_. The cornea is quite continuous

with the sclerotic but has a greater convexity. Under the microscope it

is seen to consist of five layers. Most anteriorly there is a layer of

stratified epithelium, then an anterior elastic layer, then the

_substantia propria_ of the cornea which is fibrous with spaces in which

the stellate _corneal corpuscles_ lie, while behind this is the

posterior elastic layer and then a delicate layer of endothelium. The

transparency of the cornea is due to the fact that all these structures

have the same refractive index.

The middle or vascular coat of the eye consists of the _choroid_, the

_ciliary processes_ and the _iris_. The choroid (fig. 1, ch) does not

come quite as far forward as the corneo-scleral junction: it is composed

of numerous blood-vessels and pigment cells bound together by connective

tissue and, superficially, is lined by a delicate layer of pigmented

connective tissue called the _lamina suprachoroidea_ in contact with the

already-mentioned perichoroidal lymph space. On the deep surface of the

choroid is a structureless basal lamina.

The _ciliary processes_ are some seventy triangular ridges, radially

arranged, with their apices pointing backward (fig. 1, pc), while their

bases are level with the corneo-scleral junction. They are as vascular

as the rest of the choroid, and contain in their interior the _ciliary

muscle_, which consists of radiating and circular fibres. The radiating

fibres (fig. 1, mc) rise, close to the canal of Schlemm, from the margin

of the posterior elastic lamina of the cornea, and pass backward and

outward into the ciliary processes and anterior part of the choroid,

which they pull forward when they contract. The circular fibres lie just

internal to these and are few or wanting in short-sighted people.

The _iris_ (fig. 1, I) is the coloured diaphragm of the eye, the centre

of which is pierced to form the pupil; it is composed of a connective

tissue stroma containing blood-vessels, pigment cells and muscle fibres.

In front of it is a reflection of the same layer of endothelium which

lines the back of the cornea, while behind both it and the ciliary

processes is a double layer of epithelium, deeply pigmented, which

really belongs to the retina. The pigment in the substance of the iris

is variously coloured in different individuals, and is often deposited

after birth, so that, in newly-born European children, the colour of the

eyes is often slate-blue owing to the black pigment at the back of the

iris showing through. White, yellow or reddish-brown pigment is

deposited later in the substance of the iris, causing the appearance,

with the black pigment behind, of grey, hazel or brown eyes. In

blue-eyed people very little interstitial pigment is formed, while in

Albinos the posterior pigment is also absent and the blood vessels give

the pink coloration. The muscle fibres of the iris are described as

circular and radiating, though it is still uncertain whether the latter

are really muscular rather than elastic. On to the front of the iris, at

its margin, the posterior layer of the posterior elastic lamina is

continued as a series of ridges called the _ligamentum pectinatum

iridis_, while between these ridges are depressions known as the _spaces

of Fontana_.

The inner or sensory layer of the wall of the eyeball is the _retina_;

it is a delicate transparent membrane which becomes thinner as the front

of the eye is approached. A short distance behind the ciliary processes

the nervous part of it stops and forms a scalloped border called the

_ora serrata_, but the pigmented layer is continued on behind the

ciliary processes and iris, as has been mentioned, and is known as the

_pars ciliaris retinae_ and _pars iridica retinae_. Under the microscope

the posterior part of the retina is seen to consist of eight layers. In

its passage from the lens and vitreous the light reaches these layers in

the following order:--(1) Layer of nerve fibres; (2) Layer of ganglion

cells; (3) Inner molecular layer; (4) Inner nuclear layer; (5) Outer

molecular layer; (6) Outer nuclear layer; (7) Layer of rods and cones;

(8) Pigmented layer.

The layer of nerve fibres (fig. 2, 2) is composed of the

axis-cylinders only of the fibres of the optic nerve which pierce the

sclerotic, choroid and all the succeeding layers of the retina to

radiate over its surface.

The ganglionic layer (fig. 2, 3) consists of a single stratum of large

ganglion cells, each of which is continuous with a fibre of the

preceding layer which forms its axon. Each also gives off a number of

finer processes (dendrites) which arborize in the next layer.

The inner molecular layer (fig. 2, 4) is formed by the interlacement

of the dendrites of the last layer with those of the cells of the

inner nuclear layer which comes next.

The inner nuclear layer (fig. 2, 5) contains three different kinds of

cells, but the most important and numerous are large bipolar cells,

which send one process into the inner molecular layer, as has just

been mentioned, and the other into the outer molecular layer, where

they arborize with the ends of the rod and cone fibres.

The outer molecular layer (fig. 2, 6) is very narrow and is formed by

the arborizations just described. The outer nuclear layer (fig. 2, 7),

like the inner, consists of oval cells, which are of two kinds. The

rod granules are transversely striped, and are connected externally

with the rods, while internally processes pass into the outer

molecular layer to end in a knob around which the arborizations of the

inner nuclear cells lie. The cone granules are situated more

externally, and are in close contact with the cones; internally their

processes form a foot-plate in the outer molecular layer from which

arborizations extend.

The layer of rods and cones (fig. 2, 9) contains these structures, the

rods being more numerous than the cones. The rods are spindle-shaped

bodies, of which the inner segment is thicker than the outer. The

cones are thicker and shorter than the rods, and resemble Indian

clubs, the handles of which are directed outward and are transversely

striped. In the outer part of the rods the visual purple or rhodopsin

is found.

The pigmented layer consists of a single layer of hexagonal cells

containing pigment, which is capable of moving towards the rods and

cones when the eye is exposed to light and away from them in the dark.

[Illustration: FIG. 2.--Diagrammatic section through the retina to show

the several layers, which are numbered as in the text. Ct, The radial

fibres of the supporting connective tissue.]

Supporting the delicate nervous structures of the retina are a series of

connective tissue rods known as the _fibres of Muller_ (fig. 2, Ct);

these run through the thickness of the retina at right angles to its

surface, and are joined together on the inner side of the layer of nerve

fibres to form the _inner limiting membrane_. More externally, at the

bases of the rods and cones, they unite again to form the outer limiting

membrane.

When the retina is looked at with the naked eye from in front two small

marks are seen on it. One of these is an oval depression about 3 mm.

across, which, owing to the presence of pigment, is of a yellow colour

and is known as the yellow spot (_macula lutea_); it is situated

directly in the antero-posterior axis of the eyeball, and at its margin

the nerve fibre layer is thinned and the ganglionic layer thickened. At

its centre, however, both these layers are wanting, and in the layer of

rods and cones only the cones are present. This central part is called

the _fovea centralis_ and is the point of acutest vision. The second

mark is situated a little below and to the inner side of the yellow

spot; it is a circular disk with raised margins and a depressed centre

and is called the _optic disk_; in structure it is a complete contrast

to the yellow spot, for all the layers except that of the nerve fibres

are wanting, and consequently, as light cannot be appreciated here, it

is known as the "blind spot." It marks the point of entry of the optic

nerve, and at its centre the retinal artery appears and divides into

branches. An appreciation of the condition of the optic disk is one of

the chief objects of the ophthalmoscope.

The _crystalline lens_ (fig. 1, L) with its ligament separates the

aqueous from the vitreous chamber of the eye; it is a biconvex lens the

posterior surface of which is more curved than the anterior. Radiating

from the anterior and posterior poles are three faint lines forming a Y,

the posterior Y being erect and the anterior inverted. Running from

these figures are a series of lamellae, like the layers of an onion,

each of which is made up of a number of fibrils called the lens fibres.

On the anterior surface of the lens is a layer of epithelial cells,

which, towards the margin or equator, gradually elongate into lens

fibres. The whole lens is enclosed in an elastic structureless membrane,

and, like the cornea, its transparency is due to the fact that all its

constituents have the same refractive index.

The ligament of the lens is the thickened anterior part of the hyaloid

membrane which surrounds the vitreous body; it is closely connected to

the iris at the ora serrata, and then splits into two layers, of which

the anterior is the thicker and blends with the anterior part of the

elastic capsule of the lens, so that, when its attachment to the ora

serrata is drawn forward by the ciliary muscle, the lens, by its own

elasticity, increases its convexity. Between the anterior and posterior

splitting of the hyaloid membrane is a circular lymph space surrounding

the margin of the lens known as the _canal of Petit_ (fig. 1, p).

The _aqueous humour_ (fig. 1, aq) is contained between the lens and its

ligament posteriorly and the cornea anteriorly. It is practically a very

weak solution of common salt (chloride of sodium 1.4%). The space

containing it is imperfectly divided into a large anterior and a small

posterior chamber by a perforated diaphragm--the iris.

The _vitreous body_ or _humour_ is a jelly which fills all the contents

of the eyeball behind the lens. It is surrounded by the hyaloid

membrane, already noticed, and anteriorly is concave for the reception

of the lens.

From the centre of the optic disk to the posterior pole of the lens a

lymph canal formed by a tube of the hyaloid membrane stretches through

the centre of the vitreous body; this is the _canal of Stilling_, which

in the embryo transmitted the hyaloid artery to the lens. The

composition of the vitreous is practically the same as that of the

aqueous humour.

The _arteries of the eyeball_ are all derived from the ophthalmic branch

of the internal carotid, and consist of the retinal which enters the

optic nerve far back in the orbit, the two long ciliaries, which run

forward in the choroid and join the anterior ciliaries, from muscular

branches of the ophthalmic, in the circulus iridis major round the

margin of the iris, and the six to twelve short ciliaries which pierce

the sclerotic round the optic nerve and supply the choroid and ciliary

processes.

The _veins of the eyeball_ emerge as four or five trunks rather behind

the equator; these are called from their appearance _venae vorticosae_,

and open into the superior ophthalmic vein. In addition to these there

is a retinal vein which accompanies its artery.

_Accessory Structures of the Eye._--The _eyelids_ are composed of the

following structures from in front backward: (1) Skin; (2) Superficial

fascia; (3) Orbicularis palpebrarum muscle; (4) _Tarsal plates_ of

fibrous tissue attached to the orbital margin by the superior and

inferior _palpebral ligaments_, and, at the junction of the eyelids, by

the external and internal _tarsal ligaments_ of which the latter is also

known as the _tendo oculi_; (5) _Meibomian glands_, which are large

modified sebaceous glands lubricating the edges of the lids and

preventing them adhering, and _Glands of Moll_, large sweat glands

which, when inflamed, cause a "sty"; (6) the _conjunctiva_, a layer of

mucous membrane which lines the back of the eyelids and is reflected on

to the front of the globe, the reflection forming the fornix: on the

front of the cornea the conjunctiva is continuous with the layer of

epithelial cells already mentioned.

The _lachrymal_ gland is found in the upper and outer part of the front

of the orbit. It is about the size of an almond and has an upper

(orbital) and a lower (palpebral) part. Its six to twelve ducts open on

to the superior fornix of the conjunctiva.

The _lachrymal canals_ (canaliculi) (see fig. 3, 2 and 3) are superior

and inferior, and open by minute orifices (puncta) on to the free

margins of the two eyelids near their inner point of junction. They

collect the tears, secreted by the lachrymal gland, which thus pass

right across the front of the eyeball, continually moistening the

conjunctiva. The two ducts are bent round a small pink tubercle called

the _caruncula lachrymalis_ (fig. 3, 4) at the inner angle of the

eyelids, and open into the _lachrymal sac_ (fig. 3, 5), which lies in a

groove in the lachrymal bone. The sac is continued down into the _nasal

duct_ (fig. 3, 6), which is about 3/4 inch long and opens into the

inferior meatus of the nose, its opening being guarded by a valve.

[Illustration: FIG. 3.--Lachrymal Canals and Duct.

1, Orbicular muscle. 5, Lachrymal sac.

2, Lachrymal canal. 6, Lachrymal duct.

3, Punctum. 7, Angular artery.

4, Caruncula.]

The orbit contains seven muscles, six of which rise close to the optic

foramen. The _levator palpebrae superioris_ is the highest, and passes

forward to the superior tarsal plate and fornix of the conjunctiva. The

_superior_ and _inferior recti_ are inserted into the upper and lower

surfaces of the eyeball respectively; they make the eye look inward as

well as up or down. The external and internal recti are inserted into

the sides of the eyeball and make it look outward or inward. The

superior oblique runs forward to a pulley in the inner and front part of

the roof of the orbit, round which it turns to be inserted into the

outer and back part of the eyeball. It turns the glance downward and

outward. The inferior oblique rises from the inner and front part of the

floor of the orbit, and is also inserted into the outer and back part of

the eyeball. It directs the glance upward and outward. Of all these

muscles the superior oblique is supplied by the fourth cranial nerve,

the external rectus by the sixth and the rest by the third.

The posterior part of the eyeball and the anterior parts of the muscles

are enveloped in a lymph space, known as the _capsule of Tenon_, which

assists their movements.

[Illustration:

FIG. 4. FIG. 5.

Diagram of Developing Diagram of Developing

Eye (1st stage). Eye (2nd stage).

[alpha], Forebrain. [beta], Optic cup.

[beta], Optic vesicle. [delta], Invagination of lens.

[gamma], Superficial ectoderm. Other letters as in fig. 4.]

[delta], Thickening for lens.

EMBRYOLOGY.--As is pointed out in the article BRAIN, the _optic

vesicles_ grow out from the fore-brain, and the part nearest the brain

becomes constricted and elongated to form the optic stalk (see figs. 4

and 5, [beta]). At the same time the ectoderm covering the side of the

head thickens and becomes invaginated to form the lens vesicle (see

figs. 4 and 5, [delta]), which later loses its connexion with the

surface and approaches the optic vesicle, causing that structure to

become cupped for its reception, so that what was the optic vesicle

becomes the optic cup and consists of an external and an internal layer

of cells (fig. 6 [beta] and [delta]). Of these the outer cells become

the retinal pigment, while the inner form the other layers of the

retina. The invagination of the optic cup extends, as the _choroidal

fissure_ (not shown in the diagrams), along the lower and back part of

the optic stalk, and into this slit sinks some of the surrounding

mesoderm to form the vitreous body and the hyaloid arteries, one of

which persists.[1] When this has happened the fissure closes up. The

anterior epithelium of the lens vesicle remains, but from the posterior

the lens fibres are developed and these gradually fill up the cavity.

The superficial layer of head ectoderm, from which the lens has been

invaginated and separated, becomes the anterior epithelium of the

cornea (fig. 6, [epsilon]), and between it and the lens the mesoderm

sinks in to form the cornea, iris and anterior chamber of the eye, while

surrounding the optic cup the mesoderm forms the sclerotic and choroid

coats (fig. 7, [eta] and [zeta]). Up to the seventh month the pupil is

closed by the _membrana pupillaris_, derived from the capsule of the

lens which is part of the mesodermal ingrowth through the choroidal

fissure already mentioned. The hyaloid artery remains, as a prolongation

of the retinal artery to the lens, until just before birth, but after

that its sheath forms the canal of Stilling. Most of the fibres of the

optic nerve are centripetal and begin as the axons of the ganglionic

cells of the retina; a few, however, are centrifugal and come from the

nerve cells in the brain.

[Illustration: FIG. 6.

Diagram of Developing Eye (3rd stage).

[delta], Solid lens.

[epsilon], Corneal epithelium.

Other letters as in figs. 4 and 5.]

[Illustration: FIG. 7.

Diagram of Developing Eye (4th stage). The mesodermal tissues are

dotted.

[zeta], Choroid and Iris.

[eta], Sclerotic and Cornea.

[theta], Vitreous.

[epsilon], Aqueous.

[kappa], Eyelids.]

The eyelids are developed as ectodermal folds, which blend with one

another about the third month and separate again before birth in Man

(fig. 7, [Greek: kappa]). The lachrymal sac and duct are formed from

solid ectodermal thickenings which later become canalized.

It will thus be seen that the optic nerve and retina are formed from the

brain ectoderm; the lens, anterior epithelium of the cornea, skin of the

eyelids, conjunctiva and lachrymal apparatus from the superficial

ectoderm; while the sclerotic, choroid, vitreous and aqueous humours as

well as the iris and cornea are derived from the mesoderm.

See _Human Embryology_, by C.S. Minot (New York); Quain's _Anatomy_,

vol. i. (1908); "Entwickelung des Auges der Wirbeltiere," by A.

Froriep, in _Handbuch der vergleichenden und experimentellen

Entwickelungslehre der Wirbeltiere_ (O. Hertwig, Jena, 1905).

COMPARATIVE ANATOMY.--The Acrania, as represented by Amphioxus (the

lancelet), have a patch of pigment in the fore part of the brain which

is regarded as the remains of a degenerated eye. In the Cyclostomata the

hag (Myxine) and larval lamprey (Ammocoetes) have ill-developed eyes

lying beneath the skin and devoid of lens, iris, cornea and sclerotic as

well as eye muscles. In the adult lamprey (Petromyzon) these structures

are developed at the metamorphosis, and the skin becomes transparent,

rendering sight possible. Ocular muscles are developed, but, unlike most

vertebrates, the inferior rectus is supplied by the sixth nerve while

all the others are supplied by the third. In all vertebrates the retina

consists of a layer of senso-neural cells, the rods and cones, separated

from the light by the other layers which together represent the optic

ganglia of the invertebrates; in the latter animals, however, the

senso-neural cells are nearer the light than the ganglia.

In fishes the eyeball is flattened in front, but the flat cornea is

compensated by a spherical lens, which, unlike that of other

vertebrates, is adapted for near vision when at rest. The iris in some

bony fishes (Teleostei) is not contractile. In the Teleostei, too, there

is a process of the choroid which projects into the vitreous chamber and

runs forward to the lens; it is known as the _processus falciformis_,

and, besides nourishing the lens, is concerned in accommodation. This

specialized group of fishes is also remarkable for the possession of a

so-called _choroid gland_, which is really a _rete mirabile_ (see

ARTERIES) between the choroid and sclerotic. The sclerotic in fishes is

usually chondrified and sometimes calcified or ossified. In the retina

the rods and cones are about equal in number, and the cones are very

large. In the cartilaginous fishes (Elasmobranchs) there is a silvery

layer, called the _tapetum lucidum_, on the retinal surface of the

choroid.

In the Amphibia the cornea is more convex than in the fish, but the lens

is circular and the sclerotic often chondrified. There is no processus

falciformis or tapetum lucidum, but the class is interesting in that it

shows the first rudiments of the ciliary muscle, although accommodation

is brought about by shifting the lens. In the retina the rods outnumber

the cones and these latter are smaller than in any other animals. In

some Amphibians coloured oil globules are found in connexion with the

cones, and sometimes two cones are joined, forming double or twin cones.

In Reptilia the eye is spherical and its anterior part is often

protected by bony plates in the sclerotic (Lacertilia and Chelonia). The

ciliary muscle is striated, and in most reptiles accommodation is

effected by relaxing the ciliary ligament as in higher vertebrates,

though in the snakes (Ophidia) the lens is shifted as it is in the lower

forms. Many lizards have a vascular projection of the choroid into the

vitreous, foreshadowing the pecten of birds and homologous with the

processus falciformis of fishes. In the retina the rods are scarce or

absent.

In birds the eye is tubular, especially in nocturnal and raptorial

forms: this is due to a lengthening of the ciliary region, which is

always protected by bony plates in the sclerotic. The pecten, already

mentioned in lizards, is a pleated vascular projection from the optic

disk towards the lens which in some cases it reaches. In Apteryx this

structure disappears. In the retina the cones outnumber the rods, but

are not as numerous as in the reptiles. The ciliary muscle is of the

striped variety.

In the Mammalia the eye is largely enclosed in the orbit, and bony

plates in the sclerotic are only found in the monotremes. The cornea is

convex except in aquatic mammals, in which it is flattened. The lens is

biconvex in diurnal mammals, but in nocturnal and aquatic it is

spherical. There is no pecten, but the numerous hyaloid arteries which

are found in the embryo represent it. The iris usually has a circular

pupil, but in some ungulates and kangaroos it is a transverse slit. In

the Cetacea this transverse opening is kidney-shaped, the hilum of the

kidney being above. In many carnivores, especially nocturnal ones, the

slit is vertical, and this form of opening seems adapted to a feeble

light, for it is found in the owl, among birds. The tapetum lucidum is

found in Ungulata, Cetacea and Carnivora. The ciliary muscle is

unstriped. In the retina the rods are more numerous than the cones,

while the macula lutea only appears in the Primates in connexion with

binocular vision.

Among the accessory structures of the eye the retractor bulbi muscle is

found in amphibians, reptiles, birds and many mammals; its nerve supply

shows that it is probably a derivative of the external or posterior

rectus. The nictitating membrane or third eyelid is well-developed in

amphibians, reptiles, birds and some few sharks; it is less marked in

mammals, and in Man is only represented by the little _plica

semilunaris_. When functional it is drawn across the eye by special

muscles derived from the retractor bulbi, called the _bursalis_ and

_pyramidalis_. In connexion with the nictitating membrane the Harderian

gland is developed, while the lachrymal gland secretes fluid for the

other eyelids to spread over the conjunctiva. These two glands are

specialized parts of a row of glands which in the Urodela (tailed

amphibians) are situated along the lower eyelid; the outer or posterior

part of this row becomes the lachrymal gland, which in higher

vertebrates shifts from the lower to the upper eyelid, while the inner

or anterior part becomes the Harderian gland. Below the amphibians

glands are not necessary, as the water keeps the eye moist.

The lachrymal duct first appears in the tailed amphibians; in snakes and

gecko lizards, however, it opens into the mouth.

For literature up to 1900 see R. Wiedersheim's _Vergleichende Anatomie

der Wirbeltiere_ (Jena, 1902). Later literature is noticed in the

catalogue of the Physiological Series of the R. College of Surgeons of

England Museum, vol. iii. (London, 1906). (F. G. P.)

EYE DISEASES.--The specially important diseases of the eye are those

which temporarily or permanently interfere with sight. In considering

the pathology of the eye it may be remembered that (1) it is a double

organ, while (2) either eye may have its own trouble.

1. The two eyes act together, under normal conditions, for all practical

purposes exactly as if there were but one eye placed in the middle of

the face. All impressions made upon either retina, to the one side of a

vertical line through the centre, the _fovea centralis_, before giving

rise to conscious perception cause a stimulation of the same area in the

brain. Impressions formed simultaneously, for instance, on the right

side of the right retina and on corresponding areas of the right side of

the left retina, are conveyed to the same spots in the right occipital

lobe of the brain. Pathological processes, therefore, which are

localized in the right or left occipital lobes, or along any part of the

course of the fibres which pass from the right or left optic tracts to

these "visual centres," cause defects in function of the right or left

halves of the two retinae. _Hemianopia_, or half-blindness, arising from

these pathological changes, is of very varying degrees of severity,

according to the nature and extent of the particular lesion. The blind

areas in the two fields of vision, corresponding to the outward

projection of the paralysed retinal areas, are always symmetrical both

in shape and degree. The central lesion may for instance be very small,

but at the same time destructive to the nerve tissue. This will be

revealed as a sector-shaped or insular symmetrical complete blindness in

the fields of vision to the opposite side. Or a large central area, or

an area comprising many or all of the nerve fibres which pass to the

visual centre on one side, may be involved in a lesion which causes

impairment of function, but no actual destruction of the nerve tissue.

There is thus caused a symmetrical weakening of vision (_amblyopia_) in

the opposite fields. In such cases the colour vision is so much more

evidently affected than the sense of form that the condition has been

called _hemiachromatopsia_ or half-colour blindness. Hemianopia may be

caused by haemorrhage, by embolism, by tumour growth which either

directly involves the visual nerve elements or affects them by

compression and by inflammation. Transitory hemianopia is rare and is no

doubt most frequently of toxic origin.

The two eyes also act as if they were one in accommodating. It is

impossible for the two eyes to accommodate simultaneously to different

extents, so that where there is, as occasionally happens, a difference

in focus between them, this difference remains the same for all

distances for which they are adapted. In such cases, therefore, both

eyes cannot ever be accurately adapted at the same time, though either

may be alone. It often happens as a consequence that the one eye is used

to receive the sharpest images of distant, and the other of near

objects. Any pathological change which leads to an interference in the

accommodating power of one eye alone must have its origin in a lesion

which lies peripherally to the nucleus of the third cranial nerve. Such

a lesion is usually one of the third nerve itself. Consequently, a

unilateral accommodation paresis is almost invariably associated with

pareses of some of the oculo-motor muscles. A bilateral accommodation

paresis is not uncommon. It is due to a nuclear or more central cerebral

disturbance. Unlike a hemianopia, which is mostly permanent, a double

accommodation paresis is frequently transitory. It is often a

post-diphtheritic condition, appearing alone or associated with other

paresis.

Both eyes are also normally intimately associated in their movements.

They move in response to a stimulus or a combination of stimuli,

emanating from different centres of the brain, but one which is always

equally distributed to the corresponding muscles in both eyes, so that

the two lines of fixation meet at the succession of points on which

attention is directed. The movements are thus associated in the same

direction, to the right or left, upwards or downwards, &c. In addition,

owing to the space which separates the two eyes, convergent movements,

caused by stimuli equally distributed between the two internal recti,

are required for the fixation of nearer and nearer-lying objects. These

movements would not be necessary in the case of a single eye. It would

merely have to accommodate. The converging movements of the double eye

occur in association with accommodation, and thus a close connexion

becomes established between the stimuli to accommodation and

convergence. All combinations of convergent and associated movements are

constantly taking place normally, just as if a single centrally-placed

eye were moved in all directions and altered its accommodation according

to the distance, in any direction, of the object which is fixed.

Associated and convergent movements may be interfered with

pathologically in different ways. Cerebral lesions may lead to their

impairment or complete abolition, or they may give rise to involuntary

spasmodic action, as the result of paralysing or irritating the centres

from which the various co-ordinated impulses are controlled or emanate.

Lesions which do not involve the centres may prevent the response to

associated impulses in one eye alone by interfering with the functional

activity of one or more of the nerves along which the stimuli are

conveyed. Paralysis of oculo-motor nerves is thus a common cause of

defects of association in the movements of the double eye. The great

advantage of simultaneous binocular vision--viz. the appreciation of

depth, or stereoscopic vision--is thus lost for some, or it may be all

directions of fixation. Instead of seeing singly with two eyes, there is

then double-vision (_diplopia_). This persists so long as the defect of

association continues, or so long as the habit of mentally suppressing

the image of the faultily-directed eye is not acquired.

In the absence of any nerve lesions, central or other, interfering with

their associated movements, the eyes continue throughout life to respond

equally to the stimuli which cause these movements, even when, owing to

a visual defect of the one eye, binocular vision has become impossible.

It is otherwise, however, with the proper co-ordination of convergent

movements. These are primarily regulated by the unconscious desire for

binocular vision, and more or less firmly associated with accommodation.

When one eye becomes blind, or when binocular vision for other reasons

is lost, the impulse is gradually, as it were, unlearnt. This is the

cause of _divergent concomitant squint_. Under somewhat similar

conditions a degree of convergence, which is in excess of the

requirements of fixation, may be acquired from different causes. This

gives rise to _convergent concomitant squint_.

For _Astigmatism_, &c., see the article VISION.

2. Taking each eye as a single organ, we find it to be subject to many

diseases. In some cases both eyes may be affected in the same way, e.g.

where the local disease is a manifestation of some general disturbance.

Apart from the fibrous coat of the eye, the sclera, which is little

prone to disease, and the external muscles and other adnexa, the eye may

be looked upon as composed of two elements, (a) the dioptric media, and

(b) the parts more or less directly connected with perception.

Pathological conditions affecting either of these elements may interfere

with sight.

The dioptric media, or the transparent portions which are concerned in

the transmission of light to, and the formation of images upon, the

retina, are the following: the _cornea_, the _aqueous humour_, the

_crystalline lens_ and the _vitreous humour_. Loss of transparency in

any of these media leads to blurring of the retinal images of external

objects. In addition to loss of transparency the cornea may have its

curvature altered by pathological processes. This necessarily causes

imperfection of sight. The crystalline lens, on the other hand, may be

dislocated, and thus cause image distortion.

_The Cornea._--The transparency of the cornea is mainly lost by

imflammation (_keratitis_), which causes either an infiltration of its

tissues with leucocytes, or a more focal, more destructive ulcerative

process.

Inflammation of the cornea may be primary or secondary, i.e. the

inflammatory changes met with in the corneal tissue may be directly

connected with one or more foci of inflammation in the cornea itself or

the focus or foci may be in some other part of the eye. Only the very

superficial forms of primary keratitis, those confined to the epithelial

layer, leave no permanent change; there is otherwise always a loss of

tissue resulting from the inflammation and this loss is made up for by

more or less densely intransparent connective tissue (_nebula_,

_leucoma_). These according to their site and extent cause greater or

less visual disturbance. Primary keratitis may be ulcerative or

non-ulcerative, superficial or deep, diffuse or circumscribed,

vascularized or non-vascularized. It may be complicated by deeper

inflammations of the eye such as iritis and cyclitis. In some cases the

anterior chamber is invaded by pus (_hypopyon_). The healing of a

corneal ulcer is characterized by the disappearance of pain where this

has been a symptom and by the rounding off of its sharp margins as

epithelium spreads over them from the surrounding healthy parts. Ulcers

tend to extend either in depth or superficially, rarely in both manners

at the same time. A deep ulcer leads to perforation with more or less

serious consequences according to the extent of the perforation. Often

an eye bears permanent traces of a perforation in adhesion of the iris

to the back of a corneal scar or in changes in the lens capsule

(capsular cataract). In other cases the ulcerated cornea may yield to

pressure from within, which causes it to bulge forwards (_staphyloma_).

The principal causes of primary keratitis are traumata and infection

from the conjunctiva. Traumata are most serious when the body causing

the wound is not aseptic or when micro-organisms from some other source,

often the conjunctiva and tear-sac, effect a lodgment before healing of

the wound has sufficiently advanced. In infected cases a complication

with iritis is not uncommon owing to the penetration of toxines into the

anterior chamber.

Inflammations of the cornea are the most important diseases of the eye,

because they are among the most frequent, because of the value of the

cornea to vision and because much good can often be done by judicious

treatment and much harm result from wrong interference and neglect. The

treatment of primary keratitis must vary according to the cause.

Generally speaking the aim should be to render the ulcerated portions as

aseptic as possible without using applications which are apt to cause a

great deal of irritation and thus interfere with healing. On this

account it is important to be able to recognize when healing is taking

place, for as soon as this is the case, rest, along with frequent

irrigation of the conjunctiva with sterilized water at the body

temperature, and occasionally mild antiseptic irrigation of the nasal

mucous membrane is all that is required. It is a common and dangerous

mistake to over treat.

Of local antiseptics which are of use may be mentioned the actual

cautery, chlorine water, freshly prepared silver nitrate or protargol,

and the yellow oxide of mercury. These different agents are of course

not all equally applicable in any given case; it depends upon the

severity as well as upon the nature of the inflammation which is the

most suitable. For instance, the actual cautery is employed only in the

case of the deeper septic or malignant ulcers, in which the destruction

of tissue is already considerable and tending to spread further. Again

the yellow oxide of mercury should only be used in the more superficial,

strumous forms of inflammation. Many other substances are also in use,

but need not here be referred to.

_Secondary keratitis_ takes the form of an interstitial deposit of

leucocytes between the layers of the cornea as well as often of

vascularization, sometimes intense, from the deeper network of vessels

(anterior ciliary) surrounding the cornea. The duration of a secondary

keratitis is usually prolonged, often lasting many months. More or less

complete restoration of transparency is the rule, however, eventually.

No local treatment is called for except the shading of the eyes and in

most cases the use of a mydriatic to prevent synechiae when the iris is

involved. Often it is advisable to do something for the general health.

In young people there is probably nothing better than cod-liver oil and

syrup of the iodide of iron. Inherited syphilis, tuberculous and other

inflammations are the causes of secondary keratitis.

_Neuro-paralytic Keratitis._--When the fifth nerve is paralysed there is

a tendency for the cornea to become inflamed. Different forms of

inflammation may then occur which all, besides anaesthesia, show a

marked slowness in healing. The main cause of neuro-paralytic keratitis

lies in the greater vulnerability of the cornea. The prognosis is

necessarily bad. The treatment consists in as far as possible protecting

the eye from external influences, by keeping it tied up, and by

frequently irrigating with antiseptic lotions.

Certain non-inflammatory and degenerative changes are met with in the

cornea. Of these may be mentioned _keratoconus_ or conical cornea, in

which, owing to some disturbance of vitality, the nature of which has

not been discovered, the normal curvature of the cornea becomes altered

to something more of a hyberboloid of revolution, with consequent

impairment of vision: _arcus senilis_, a whitish opacity due to fatty

degeneration, extending round the corneal margin, varying in thickness

in different subjects and usually only met with in old people:

_transverse calcareous film_, consisting of a finely punctiform opacity

extending, in a tolerably uniformly wide band, occupying the zone of the

cornea which is left uncovered when the lids are half closed.

Tumours of the cornea are not common. Those chiefly met with are

dermoids, fibromata, sarcomata and epitheliomata.