HEARING HEIDEGGER, JOHANN HEINRICH
HEARN, LAFCADIO HEIDELBERG (town of Germany)
HEARNE, SAMUEL HEIDELBERG (town of Transvaal)
HEARNE, THOMAS HEIDELBERG CATECHISM, THE
HEARSE HEIDELOFF, KARL ALEXANDER VON
HEART HEIDENHEIM
HEART-BURIAL HEIFER
HEARTH HEIGEL, KARL AUGUST VON
HEARTS HEIJERMANS, HERMANN
HEAT HEILBRONN
HEATH, BENJAMIN HEILIGENSTADT
HEATH, NICHOLAS HEILSBERG
HEATH, WILLIAM HEILSBRONN
HEATH HEIM, ALBERT VON ST GALLEN
HEATHCOAT, JOHN HEIM, FRANCOIS JOSEPH
HEATHCOTE, SIR GILBERT HEIMDAL
HEATHEN HEINE, HEINRICH
HEATHFIELD, GEORGE ELIOTT HEINECCIUS, JOHANN GOTTLIEB
HEATING HEINECKEN, CHRISTIAN HEINRICH
HEAVEN HEINICKE, SAMUEL
HEBBEL, CHRISTIAN FRIEDRICH HEINSE, JOHANN JAKOB WILHELM
HEBBURN HEINSIUS, DANIEL
HEBDEN BRIDGE HEINSIUS, NIKOLAES
HEBE HEIR
HEBEL, JOHANN PETER HEIRLOOM
HEBER, REGINALD HEJAZ
HEBER, RICHARD HEJIRA
HEBERDEN, WILLIAM HEL
HEBERT, EDMOND HELDENBUCH, DAS
HEBERT, JACQUES RENE HELDER
HEBREW LANGUAGE HELEN
HEBREW LITERATURE HELENA, ST
HEBREW RELIGION HELENA (Arkansas, U.S.A.)
HEBREWS, EPISTLE TO THE HELENA (Montana, U.S.A.)
HEBRIDES, THE HELENSBURGH
HEBRON HELENUS
HECATAEUS OF ABDERA HELGAUD
HECATAEUS OF MILETUS HELGESEN, POVL
HECATE HELIACAL
HECATOMB HELIAND
HECATO OF RHODES HELICON (mountain range)
HECKER, FRIEDRICH FRANZ KARL HELICON (contrabass tuba)
HECKER, ISAAC THOMAS HELIGOLAND
HECKMONDWIKE HELIOCENTRIC
HECTOR HELIODORUS
HECUBA HELIOGABALUS (ELAGABALUS)
HEDA, WILLEM CLAASZ HELIOGRAPH
HEDDLE, MATTHEW FORSTER HELIOMETER
HEDGEHOG HELIOPOLIS
HEDGES AND FENCES HELIOSTAT
HEDON HELIOTROPE
HEDONISM HELIOZOA
HEEL HELIUM
HEEM, JAN DAVIDSZ VAN HELIX
HEEMSKERK, JOHAN VAN HELL
HEEMSKERK, MARTIN JACOBSZ HELLANICUS
HEER, OSWALD HELLEBORE
HEEREN, ARNOLD HERMANN LUDWIG HELLENISM
HEFELE, KARL JOSEF VON HELLER, STEPHEN
HEGEL, GEORG WILHELM FRIEDRICH HELLESPONT
HEGEMON OF THASOS HELLEVOETSLUIS
HEGEMONY HELLIN
HEGESIAS OF MAGNESIA HELLO, ERNEST
HEGESIPPUS (Athenian orator) HELMERS, JAN FREDERIK
HEGESIPPUS (early Christian writer) HELMERSEN, GREGOR VON
HEGESIPPUS (author of Jewish War) HELMET
HEGIUS [VON HEEK], ALEXANDER HELMHOLTZ, HERMANN LUDWIG VON
HEIBERG, JOHAN LUDVIG HELMOLD (historian)
HEIDE HELMOND (town in Holland)
HEARING (formed from the verb "to hear," O. Eng. _hyran_, _heran_, &c.,
a common Teutonic verb; cf. Ger. _horen_, Dutch _hooren_, &c.; the O.
Teut. form is seen in Goth. _hausjan_; the initial _h_ makes any
connexion with "ear," Lat. _audire_, or Gr. [Greek: akouein] very
doubtful), in physiology, the function of the ear (q.v.), and the
general term for the sense or special sensation, the cause of which is
an excitation of the auditory nerves by the vibrations of sonorous
bodies. The anatomy of the ear is described in the separate article on
that organ. A description of sonorous vibrations is given in the article
SOUND; here we shall consider the transmission of such vibrations from
the external ear to the auditory nerve, and the physiological characters
of auditory sensation.
1. _Transmission in External Ear._--The external ear consists of the
_pinna_, or auricle, and the _external auditory meatus_, or canal, at
the bottom of which we find the _membrana tympani_, or drum head. In
many animals the auricle is trumpet-shaped, and, being freely movable by
muscles, serves to collect sonorous waves coming from various
directions. The auricle of the human ear presents many irregularities of
surface. If these irregularities are abolished by filling them up with a
soft material such as wax or oil, leaving the entrance to the canal
free, experiment shows that the intensity of sounds is weakened, and
that there is more difficulty in judging of their direction. When waves
of sound strike the auricle, they are partly reflected outwards, while
the remainder, impinging at various angles, undergo a number of
reflections so as to be directed into the auditory canal. Vibrations are
transmitted along the auditory canal, partly by the air it contains and
partly by its walls, to the membrana tympani. The absence of the
auricle, as the result of accident or injury, does not cause diminution
of hearing. In the auditory canal waves of sound are reflected from side
to side until they reach the membrana tympani. From the obliquity in
position and peculiar curvature of this membrane, most of the waves
strike it nearly perpendicularly, and in the most advantageous
direction.
2. _Transmission in Middle Ear._--The middle ear is a small cavity, the
walls of which are rigid with the exception of the portions consisting
of the membrana tympani, and the membrane of the round window and of the
apparatus filling the oval window. This cavity communicates with the
pharynx by the _Eustachian tube_, which forms an air-tube between the
pharynx and the tympanum for the purpose of regulating pressure on the
membrana tympani. During rest the tube is open, but it is closed during
the act of deglutition. As this action is frequently taking place, not
only when food or drink is introduced, but when saliva is swallowed, it
is evident that the pressure of the air in the tympanum will be kept in
a state of equilibrium with that of the external air on the outer
surface of the membrana tympani, and that thus the membrana tympani will
be rendered independent of variations of atmospheric pressure such as
occur when we descend in a diving bell or ascend in a balloon. By a
forcible expiration, the oral and nasal cavities being closed, air may
be driven into the tympanum, while a forcible inspiration (Valsalva's
experiment) will draw air from that cavity. In the first case, the
membrana tympani will bulge outwards, in the second case inwards, and in
both, from excessive stretching of the membrane, there will be partial
deafness, especially for sounds of high pitch. Permanent occlusion of
the tube is one of the most common causes of deafness.
The membrana tympani is capable of being set into vibration by a sound
of any pitch included in the range of perceptible sounds. It responds
exactly as to number of vibrations (pitch), intensity of vibrations
(intensity), and complexity of vibration (quality or timbre).
Consequently we can hear a sound of any given pitch, of a certain
intensity, and in its own specific timbre or quality. Generally
speaking, very high tones are heard more easily than low tones of the
same intensity. As the membrana tympani is not only fixed by its margin
to a ring or tube of bone, but is also adherent to the handle of the
malleus, which follows its movements, its vibrations meet with
considerable resistance. This diminishes the intensity of its
vibrations, and prevents also the continued vibration of the membrane
after an external pressure has ceased, so that a sound is not heard much
longer than its physical cause lasts. The tension of the membrane may be
affected (1) by differences of pressure on the two surfaces of the
membrana tympani, as may occur during forcible expiration or
inspiration, and (2) by muscular action, due to contraction of the
_tensor tympani_ muscle. This small muscle arises from the apex of the
petrous temporal and the cartilage of the Eustachian tube, enters the
tympanum at its anterior wall, and is inserted into the malleus near its
root. The handle of the malleus is inserted between the layers of the
membrana tympani, and, as the malleus and incus move round an axis
passing through the neck of the malleus from before backwards, the
action of the muscle is to pull the membrana tympani inwards towards the
tympanic cavity in the form of a cone, the meridians of which are not
straight but curved, with convexity outwards. When the muscle contracts,
the handle of the malleus is drawn still farther inwards, and thus a
greater tension of the tympanic membrane is produced. On relaxation of
the muscle, the membrane returns to its position of equilibrium by its
elasticity and by the elasticity of the chain of bones. This power of
varying the tension of the membrane is an accommodating mechanism for
receiving and transmitting sounds of different pitch. With different
degrees of tension it will respond more readily to sounds of different
pitch. Thus, when the membrane is tense, it will readily respond to high
sounds, while relaxation will be the condition most adapted for low
tones. In addition, increased tension of the membrane, by increasing the
resistance, will diminish the intensity of vibrations. This is
especially the case for sounds of low pitch.
The vibrations of the membrana tympani are transmitted to the internal
ear partly by the air which the middle ear or tympanum contains, and
partly by the chain of bones, consisting of the malleus, incus and
stapes. Of these, transmission by the chain of bones is by far the most
important. In birds and in the amphibia, this chain is represented by a
single rod-like ossicle, the _columella_, but in man the two
membranes--the membrana tympani and the membrane filling the fenestra
ovalis--are connected by a compound lever consisting of three bones,
namely, the _malleus_, or hammer, inserted into the membrana tympani,
the _incus_, or anvil, and the _stapes_, or stirrup, the base of which
is attached to a membrane covering the oval window. It must also be
noted that in the transmission of vibrations of the membrana tympani to
the fluid in the labyrinth or internal ear, through the oval window, the
chain of ossicles vibrates as a whole and acts efficiently, although its
length may be only a fraction of the wave-length of the sound
transmitted. The chain is a lever in which the handle of the malleus
forms the long arm, the fulcrum is where the short process of the incus
abuts against the wall of the tympanum, while the long process of the
incus, carrying the stapes, forms the short arm. The mechanism is a
lever of the second order. Measurements show that the ratio of the
lengths of the two arms is as 1.5 : 1; the ratio of the resulting force
at the stapes is therefore as 1 : 1.5; while the amplitudes of the
movements at the tip of the handle of the malleus and the stapes is as
1.5 : 1. Hence, while there is a diminution in amplitude there is a gain
in power, and thus the pressures are conveyed with great efficiency from
the membrana tympani to the labyrinth, while the amplitude of the
oscillation is diminished so as to be adapted to the small capacity of
the labyrinth. As the drum-head is nearly twenty times greater in area
than the membrane covering the oval window, with which the base of the
stapes is connected, the energy of the movements of the membrana tympani
is concentrated on an area twenty times smaller; hence the pressure is
increased thirtyfold (1.5 X 20) when it acts at the base of the stapes.
Experiments on the human ear have shown that the movement of greatest
amplitude was at the tip of the handle of the malleus, 0.76 mm.; the
movement of the tip of the long arm process of the incus was 0.21 mm.;
while the greatest amplitude at the base of the stapes was only .0714
mm. Other observations have shown the movements at the stapes to have a
still smaller amplitude, varying from 0.001 to 0.032 mm. With tones of
feeble intensity the movements must be almost infinitesimal. There may
also be very minute transverse movements at the base of the stapes.
3. _Transmission in the Internal Ear._--The internal ear is composed of
the labyrinth, formed of the vestibule or central part, the semicircular
canals, and the cochlea, each of which consists of an osseous and a
membranous portion. The osseous labyrinth may be regarded as an osseous
mould in the petrous portion of the temporal bone, lined by tesselated
endothelium, and containing a small quantity of fluid called the
_perilymph_. In this mould, partially surrounded by, and to some extent
floating in, this fluid, there is the membranous labyrinth, in certain
parts of which we find the terminal apparatus in connexion with the
auditory nerve, immersed in another fluid called the _endolymph_. The
membranous labyrinth consists of a vestibular portion formed by two
small sac-like dilatations, called the _saccule_ and the _utricle_, the
latter of which communicates with the semicircular canals by five
openings. Each canal consists of a tube, bulging out at each extremity
so as to form the so-called _ampulla_, in which, on a projecting ridge,
called the _crista acustica_, there are cells bearing long _auditory
hairs_, which are the peripheral end-organs of the vestibular branches
of the auditory nerve. The cochlear division of the membranous labyrinth
consists of the _ductus cochlearis_, a tube of triangular form fitting
in between the two cavities in the cochlea, called the _scala
vestibuli_, because it commences in the vestibule, and the _scala
tympani_, because it ends in the tympanum, at the round window. These
two scalae communicate at the apex of the cochlea. The roof of the
ductus cochlearis is formed by a thin membrane called the _membrane of
Reissner_, while its floor consists of the _basilar membrane_, on which
we find the remarkable _organ of Corti_, which constitutes the terminal
organ of the cochlear division of the auditory nerve. It is sufficient
to state here that this organ consists essentially of an arrangement of
epithelial cells bearing hairs which are in communication with the
terminal filaments of this portion of the auditory nerve, and that
groups of these hairs pass through holes in a closely investing
membrane, _membrana reticularis_, which may act as a damping apparatus,
so as quickly to stop their movements. The ductus cochlearis and the two
scalae are filled with fluid. Sonorous vibrations may reach the fluid in
the labyrinth by three different ways--(1) by the osseous walls of the
labyrinth, (2) by the air in the tympanum and the round window, and (3)
by the base of the stapes inserted into the oval window.
When the head is plunged into water, or brought into direct contact with
any vibrating body, vibrations must be transmitted directly. Vibrations
of the air in the mouth and in the nasal passages are also communicated
directly to the walls of the cranium, and thus pass to the labyrinth. In
like manner, we may experience auditive sensations, such as blowing,
rubbing and hissing sounds, due to muscular contraction or to the
passage of blood in vessels close to the auditory organ. It is doubtful
whether any vibrations are communicated to the fluid in the labyrinth by
the round window. Vibrations which cause hearing are communicated by the
chain of bones. When the base of the stirrup is pushed into the oval
window, the pressure in the labyrinth increases, and, as the only mobile
part of the wall of the labyrinth is the membrane covering the round
window, this membrane is forced outwards; when the base of the stirrup
moves outwards a reverse action takes place. Thus the fluid of the
labyrinth receives a series of pulses isochronous with the movements of
the base of the stirrup, and these pulses affect the terminal apparatus
in connexion with the auditory nerve.
The sacs of the internal ear, known as the utricle and saccule, receive
the impulses of the base of the stapes. They are organs connected with
the perception of sounds as sounds, without reference to pitch or
quality. For the _analysis_ of tone a cochlea is necessary. Even in
mammals all the parts of the ear may be destroyed or affected by
disease, except these sacs, without causing complete deafness.
It has been suggested by Lee (_Amer. Jour. of Physiol._ vol. i. No. 1,
p. 128) that in fishes the sac has nothing to do with hearing, but
serves for the perception of movements, such as those of rotation and
translation through space, movements much coarser than those that form
the physical basis of sound. He considers, also, that as fishes, with
few exceptions, are dumb, they are also deaf. In the fish there are
peculiar organs along the lateral line which are known to be connected
with the perception of movements of the body as a whole, and Beard
(_Zool. Anz. Leipzig_, 1884, Bd. vii. S. 140) has attempted to trace a
phylogenetic connexion between the sacs of the internal ear and the
organs in the lateral line. According to this view, when animals became
air-breathers, a part of the ear (the _papilla acustica basilaris_) was
gradually evolved for the perception of delicate vibrations of sound.
(See EQUILIBRIUM.)
It is by means of the cochlea that we discriminate pitch, hear beats,
and are affected by quality of tone.
Since the size of the membranous labyrinth is so small, measuring, in
man, not more than 1/2 in. in length by 1/8 in. in diameter at its
widest part, and since it is a chamber consisting partly of conduits of
very irregular form, it is impossible to state accurately the course of
vibrations transmitted to it by impulses communicated from the base of
the stirrup. In the cochlea vibrations must pass from the saccule along
the scala vestibuli to the apex, thus affecting the membrane of
Reissner, which forms its roof; then, passing through the opening at the
apex (the _helicotrema_), they must descend by the scala tympani to the
round window, and affect in their passage the membrana basilaris, on
which the organ of Corti is situated. From the round window impulses
must be reflected backwards, but how they affect the advancing impulses
is not known. But the problem is even more complex when we take into
account the fact that impulses are transmitted simultaneously to the
utricle and to the semicircular canals communicating with it by five
openings. The mode of action of these vibrations or impulses upon the
nervous terminations is still unknown; but to appreciate critically the
hypothesis which has been advanced to explain it, it is necessary, in
the first place, to refer to some of the general characters of auditory
sensation.
4. _General Characters of Auditory Sensations._--Certain conditions are
necessary for excitation of the auditory nerve sufficient to produce a
sensation. In the first place, the vibrations must have a certain
_amplitude_ and _energy_; if too feeble, no impression will be produced.
Various physicists have attempted to measure the sensitiveness of the
ear by estimating the amplitude of the molecular movements necessary to
call forth the feeblest audible sound. Thus A. Topler and L. Boltzmann,
on data founded on experiments with organ pipes, state that the ear is
affected by vibrations of molecules of the air not more in amplitude
than .0004 mm. at the ear, or 0.1 of the wave-length of green light, and
that the energy of such a vibration on the drum-head is not more than
1/543 billionth kilog., or 1/17th of that produced upon an equal surface
of the retina by a single candle at the same distance (_Ann. d. Phys. u.
Chem._, Leipzig. 1870, Bd. cxli. S. 321). Lord Rayleigh, by two other
methods, arrived at the conclusion "that the streams of energy required
to influence the eye and ear are of the same order of magnitude." He
estimated the amplitude of the movement of the aerial particles, with a
sound just audible, as less than the ten-millionth of a centimetre, and
the energy emitted when the sound was first becoming audible, at 42.1
ergs per second. He also states that in considering the amplitude or
condensation in progressive aerial waves, at a distance of 27.4 metres
from a tuning-fork, the maximum condensation was = 6.0 X 10^-9 cm., a
result showing "that the ear is able to recognize the addition or
subtraction of densities far less than those to be found in our highest
vacua" (_Proc. Roy. Soc._, 1877, vol. xxvi. p. 248; _Lond. Edin. and
Dub. Phil. Mag._, 1894, vol. xxxviii. p. 366).
In the next place, vibrations must have a certain _duration_ to be
perceived; and lastly, to excite a sensation of a continuous musical
sound, a certain _number_ of impulses must occur in a given interval of
time. The lower limit is about 30, and the upper about 30,000 vibrations
per second. Below 30, the individual impulses may be observed, and above
30,000 few ears can detect any sound at all. The extreme upper limit is
not more than 35,000 vibrations per second. Auditory sensations are of
two kinds--noises and musical sounds. _Noises_ are caused by impulses
which are not regular in intensity or duration, or are not periodic, or
they may be caused by a series of musical sounds occurring
instantaneously so as to produce discords, as when we place our hand at
random on the keyboard of a piano. _Musical tones_ are produced by
periodic and regular vibrations. In musical sounds three characters are
prominent--intensity, pitch and quality. _Intensity_ depends on the
amplitude of the vibration, and a greater or lesser amplitude of the
vibration will cause a corresponding movement of the transmitting
apparatus, and a corresponding intensity of excitation of the terminal
apparatus. _Pitch_, as a sensation, depends on the length of time in
which a single vibration is executed, or, in other words, the number of
vibrations in a given interval of time. The ear is capable of
appreciating the relative pitch or height of a sound as compared with
another, although it may not ascertain precisely the absolute pitch of a
sound. What we call an acute or high tone is produced by a large number
of vibrations, while a grave or low tone is caused by few. The musical
tones which can be used with advantage range between 40 and 4000
vibrations per second, extending thus from 6 to 7 octaves. According to
E. H. Weber, practised musicians can perceive a difference of pitch
amounting to only the 1/64th of a semitone, but this is far beyond
average attainment. In a few individuals, and especially in early life,
there may be an appreciation of absolute pitch. _Quality_ or _timbre_
(or _Klang_) is that peculiar characteristic of a musical sound by which
we may identify it as proceeding from a particular instrument or from a
particular human voice. It depends on the fact that many waves of sound
that reach the ear are compound wave systems, built up of constituent
waves, each of which is capable of exciting a sensation of a simple tone
if it be singled out and reinforced by a resonator (see SOUND), and
which may sometimes be heard without a resonator, after special practice
and tuition. Thus it appears that the ear must have some arrangement by
which it resolves every wave system, however complex, into simple
pendular vibrations. When we listen to a sound of any quality we
recognize that it is of a certain pitch. This depends on the number of
vibrations of one tone, predominant in intensity over the others, called
the fundamental or ground tone, or first partial tone. The quality, or
timbre, depends on the number and intensity of other tones added to it.
These are termed _harmonic_ or _partial tones_, and they are related to
the first partial or fundamental tone in a very simple manner, being
multiples of the fundamental tone: thus--
Fundamental Upper Partials or Harmonics.
Tone
Notes do^1 do^2 sol^2 do^3 mi^3 sol^3 si[flat]^3 do^4 re^4 mi^4
Partial tones 1 2 3 4 5 6 7 8 9 10
Number of
vibrations 33 66 99 132 165 198 231 264 297 330
When a simple tone, or one free from partials, is heard, it gives rise
to a simple, soft, somewhat insipid sensation, as may be obtained by
blowing across the mouth of an open bottle or by a tuning-fork. The
lower partials added to the fundamental tone give softness combined with
richness; while the higher, especially if they be very high, produce a
brilliant and thrilling effect, as is caused by the brass instruments of
an orchestra. Such being the facts, how may they be explained
physiologically?
Little is yet known regarding the mode of action of the vibrations of
the fluid in the labyrinth upon the terminal apparatus connected with
the auditory nerve. There can be no doubt that it is a mechanical
action, a communication of impulses to delicate hair-like processes, by
the movements of which the nervous filaments are irritated. In the human
ear it has been estimated that there are about 3000 small arches formed
by the _rods of Corti._ Each arch rests on the basilar membrane, and
supports rows of cells having minute hair-like processes. It would
appear also that the filaments of the auditory nerve terminate in the
basilar membrane, and possibly they may be connected with the
hair-cells. At one time it was supposed by Helmholtz that these fibres
of Corti were elastic and that they were tuned for particular sounds, so
as to form a regular series corresponding to all the tones audible to
the human ear. Thus 2800 fibres distributed over the tones of seven
octaves would give 400 fibres for each octave, or nearly 33 for a
semitone. Helmholtz put forward the hypothesis that, when a pendular
vibration reaches the ear, it excites by sympathetic vibration the fibre
of Corti which is tuned for its proper number of vibrations. If, then,
different fibres are tuned to tones of different pitch, it is evident
that we have here a mechanism which, by exciting different nerve fibres,
will give rise to sensations of pitch. When the vibration is not simple
but compound, in consequence of the blending of vibrations corresponding
to various harmonics or partial tones, the ear has the power of
resolving this compound vibration into its elements. It can only do so
by different fibres responding to the constituent vibrations of the
sound--one for the fundamental tone being stronger, and giving the
sensation of a particular pitch to the sound, and the others,
corresponding to the upper partial tones, being weaker, and causing
undefined sensations, which are so blended together in consciousness as
to terminate in a complex sensation of a tone of a certain quality or
timbre. It would appear at first sight that 33 fibres of Corti for a
semitone are not sufficient to enable us to detect all the gradations of
pitch in that interval, since, as has been stated above, trained
musicians may distinguish a difference of 1/64th of a semitone. To meet
this difficulty, Helmholtz stated that if a sound is produced, the pitch
of which may be supposed to come between two adjacent fibres of Corti,
both of these will be set into sympathetic vibration, but the one which
comes nearest to the pitch of the sound will vibrate with greater
intensity than the other, and that consequently the pitch of that sound
would be thus appreciated. These theoretical views of Helmholtz have
derived much support from experiments of V. Hensen, who observed that
certain hairs on the antennae of _Mysis_, a Crustacean, when seen with a
low microscopic power, vibrated with certain tones produced by a keyed
horn. It was seen that certain tones of the horn set some hairs into
strong vibration, and other tones other hairs. Each hair responded also
to several tones of the horn. Thus one hair responded strongly to
d[sharp] and d'[sharp], more weakly to g, and very weakly to G. It was
probably tuned to some pitch between d" and d"[sharp]. (_Studien uber
das Gehororgan der Decapoden_, Leipzig, 1863.)
Histological researches have led to a modification of this hypothesis.
It has been found that the rods or arches of Corti are stiff structures,
not adapted for vibrating, but apparently constituting a support for the
hair-cells. It is also known that there are no rods of Corti in the
cochlea of birds, which are capable nevertheless of appreciating pitch.
Hensen and Helmholtz suggested the view that not only may the segments
of the membrana basilaris be stretched more in the radial than in the
longitudinal direction, but different segments may be stretched radially
with different degrees of tension so as to resemble a series of tense
strings of gradually increasing length. Each string would then respond
to a vibration of a particular pitch communicated to it by the
hair-cells. The exact mechanism of the hair-cells and of the membrana
reticularis, which looks like a damping apparatus, is unknown.
5. _Physiological Characters of Auditory Sensation._--Under ordinary
circumstances auditory sensations are referred to the outer world. When
we hear a sound, we associate it with some external cause, and it
appears to originate in a particular place or to come in a particular
direction. This feeling of _exteriority_ of sound seems to require
transmission through the membrana tympani. Sounds which are sent through
the walls of the cranium, as when the head is immersed in, and the
external auditory canals are filled with, water, appear to originate in
the body itself.
An auditory sensation lasts a short time after the cessation of the
exciting cause, so that a number of separate vibrations, each capable of
exciting a distinct sensation if heard alone, may succeed each other so
rapidly that they are fused into a single sensation. If we listen to the
puffs of a syren, or to vibrating tongues of low pitch, the single
sensation is usually produced by about 30 or 35 vibrations per second;
but when we listen to beats of considerable intensity, produced by two
adjacent tones of sufficiently high pitch, the ear may follow as many as
132 intermissions per second.
The sensibility of the ear for sounds of different pitch is not the
same. It is more sensitive for acute than for grave sounds, and it is
probable that the maximum degree of acuteness is for sounds produced by
about 3000 vibrations per second, that is near fa^5[sharp]. Sensibility
as to pitch varies much with the individual. Thus some musicians may
detect a difference of 1/1000th of the total number of vibrations, while
other persons may have difficulty in appreciating a semitone.
6. _Analytical Power of the Ear._--When we listen to a compound tone,
we have the power of picking out these partials from the general mass
of sound. It is known that the frequencies of the partials as compared
with that of the fundamental tone are simple multiples of the
frequency of the fundamental, and also that physically the waves of
the partials so blend with each other as to produce waves of very
complicated forms. Yet the ear, or the ear and the brain together, can
resolve this complicated wave-form into its constituents, and this is
done more easily if we listen to the sound with resonators, the pitch
of which corresponds, or nearly corresponds, to the frequencies of the
partials. Much discussion has taken place as to how the ear
accomplishes this analysis. All are agreed that there is a complicated
apparatus in the cochlea which may serve this purpose; but while some
are of opinion that this structure is sufficient, others hold that the
analysis takes place in the brain. When a complicated wave falls on
the drum-head, it must move out and in in a way corresponding to the
variations of pressure, and these variations will, in a single
vibration, depend on the greater or less degree of complexity of the
wave. Thus a single tone will cause a movement like that of a
pendulum, a simple pendular vibration, while a complex tone, although
occurring in the same duration of time, will cause the drum-head to
move out and in in a much more complicated manner. The complex
movement will be conveyed to the base of the stapes, thence to the
vestibule, and thence to the cochlea, in which we find the ductus
cochlearis containing the organ of Corti. It is to be noted also that
the parts in the cochlea are so small as to constitute only a fraction
of the wave-length of most tones audible to the human ear. Now it is
evident that the cochlea must act either as a whole, all the nerve
fibres being affected by any variations of pressure, or the nerve
fibres may have a selective action, each fibre being excited by a wave
of a definite period, or there may exist small vibratile bodies
between the nerve filaments and the pressures sent into the organ. The
last hypothesis gives the most rational explanation of the phenomena,
and on it is founded a theory generally accepted and associated with
the names of Thomas Young and Hermann Helmholtz. It may be shortly
stated as follows:--
"(1) In the cochlea there are vibrators, tuned to frequencies within
the limits of hearing, say from 30 to 40,000 or 50,000 vibs. per
second. (2) Each vibrator is capable of exciting its appropriate nerve
filament or filaments, so that a nervous impulse, corresponding to the
frequency of the vibrator, is transmitted to the brain--not
corresponding necessarily, as regards the number of nervous impulses,
but in such a way that when the impulses along a particular nerve
filament reach the brain, a state of consciousness is aroused which
does correspond with the number of the physical stimuli and with the
period of the auditory vibrator. (3) The mass of each vibrator is such
that it will be easily set in motion, and after the stimulus has
ceased it will readily come to rest. (4) Damping arrangements exist in
the ear, so as quickly to extinguish movements of the vibrators. (5)
If a simple tone falls on the ear, there is a pendular movement of the
base of the stapes, which will affect all the parts, causing them to
move; but any part whose natural period is nearly the same as that of
the sound will respond on the principle of sympathetic resonance, a
particular nerve filament or nerve filaments will be affected, and a
sensation of a tone of definite pitch will be experienced, thus
accounting for discrimination in pitch. (6) Intensity or loudness will
depend on the amplitude of movement of the vibrating body, and
consequently on the intensity of nerve stimulation. (7) If a compound
wave of pressure be communicated by the base of the stapes, it will be
resolved into its constituents by the vibrators corresponding to tones
existing in it, each picking out its appropriate portion of the wave,
and thus irritating corresponding nerve filaments, so that nervous
impulses are transmitted to the brain, where they are fused in such a
way as to give rise to a sensation of a particular quality or
character, but still so imperfectly fused that each constituent, by a
strong effort of attention, may be specially recognized" (article
"Ear," by M'Kendrick, Schafer's _Text-Book_, _loc. cit._).
The structure of the ductus cochlearis meets the demands of this
theory, it is highly differentiated, and it can be shown that in it
there are a sufficient number of elements to account for the delicate
appreciation of pitch possessed by the human ear, and on the basis
that the highly trained ear of a violinist can detect a difference of
1/64th of a semitone (M'Kendrick, _Trans. Roy. Soc. Ed._, 1896, vol.
xxxviii. p. 780; also Schafer's _Text-Book_, loc. cit.). Measurements
of the cochlea have also shown such differentiation as to make it
difficult to imagine that it can act as a whole. A much less complex
organ might have served this purpose (M'Kendrick, _op. cit._). The
following table, given by Retzius (_Das Gehororgan der Wirbelthiere_,
Bd. ii. S. 356), shows differentiations in the cochlea of man, the cat
and the rabbit, all of which no doubt hear tones, although in all
probability they have very different powers of discrimination:--
Man. Cat. Rabbit.
Ear-teeth 2,490 2,430 1,550
Holes in habenula for nerves 3,985 2,780 1,650
Inner rods of Corti's organ 5,590 4,700 2,800
Outer rods of Corti's organ 3,848 3,300 1,900
Inner hair-cells (one row) 3,487 2,600 1,600
Outer hair-cells (several rows) 11,750 9,900 6,100
Fibres in basilar membrane 23,750 15,700 10,500
7. _Dissonance._--The theory can also be used to explain dissonance.
When two tones sufficiently near in pitch are simultaneously sounded,
beats are produced. If the beats are few in number they can be
counted, because they give rise to separate and distinct sensations;
but if they are numerous they blend so as to give roughness or
dissonance to the interval. The roughness or dissonance is most
disagreeable with about 33 beats falling on the ear per second. When
two compound tones are sounded, say a minor third on a harmonium in
the lower part of the keyboard, then we have beats not only between
the primaries, but also between the upper partials of each of the
primaries. The beating distance may, for tones of medium pitch, be
fixed at about a minor third, but this interval will expand for
intervals on low tones and contract for intervals on high ones. This
explains why the same interval in the lower part of the scale may give
slow beats that are not disagreeable, while in the higher part it may
cause harsh and unpleasant dissonance. The partials up to the seventh
are beyond beating distance, but above this they come close together.
Consequently instruments (such as tongues, or reeds) that abound in
upper partials cause an intolerable dissonance if one of the primaries
is slightly out of tune. Some intervals are pleasant and satisfying
when produced on instruments having few partials in their tones. These
are concords. Others are less so, and they may give rise to an
uncomfortable sensation. These are discords. In this way unison, 1/1,
minor third 6/5, major third 5/4, fourth 4/3, fifth 3/2, minor sixth
8/5, major sixth 5/3 and octave 2/1, are all concords; while a second
9/8, minor seventh 16/9 and major seventh 15/8, are discords.
Helmholtz compares the sensation of dissonance to that of a flickering
light on the eye. "Something similar I have found to be produced by
simultaneously stimulating the skin, or margin of the lips, by
bristles attached to tuning-forks giving forth beats. If the frequency
of the forks is great, the sensation is that of a most disagreeable
tickling. It may be that the instinctive effort at analysis of tones
close in pitch causes the disagreeable sensation" (Schafer's
_Text-Book_, _op. cit._ p. 1187).
8. _Other Theories._--In 1865 Rennie objected to the analysis theory,
and urged that the cochlea acted as a whole (_Ztschr. f. rat. Med._,
Dritte Reihe, Bd. xxiv. Heft 1, S. 12-64). This view was revived by
Voltolini (Virchow's _Archiv_, Bd. c. S. 27) some years later, and in
1886 it was urged by E. Rutherford (_Rep. Brit. Assoc. Ad. Sc._,
1886), who compared the action of the cochlea to that of a telephone
plate. According to this theory, all the hairs of the auditory cells
vibrate to every note, and the hair-cells transform sound vibrations
into nerve vibrations or impulses, similar in frequency, amplitude and
character to the sound vibrations. There is no analysis in the
peripheral organ. A. D. Waller, in 1891 (_Proc. Physiol. Soc._, Jan.
20, 1891) suggested that the basilar membrane as a whole vibrates to
every note, thus repeating the vibrations of the membrana tympani; and
since the hair-cells move with the basilar membrane, they produce what
may be called pressure patterns against the tectorial membranes, and
filaments of the auditory nerve are stimulated by these pressures.
Waller admits a certain degree of peripheral analysis, but he
relegates ultimate analysis to the brain. These theories, dispensing
with peripheral analysis, leave out of account the highly complex
structure of the cochlea, or, in other words, they assign to that
structure a comparatively simple function which could be performed by
a simple membrane capable of vibrating. We find that the cochlea
becomes more elaborate as we ascend the scale of animals, until in
man, who possesses greater powers of analysis than any other being,
the number of hair-cells, fibres of the basilar membrane and arches of
Corti are all much increased in number (see Retzius's table, _supra_).
The principle of sympathetic resonance appears, therefore, to offer
the most likely solution of the problem. Hurst's view is that with
each movement of the stapes a wave is generated which travels up the
scala vestibuli, through the helicotrema into the scala tympani and
down the latter to the fenestra rotunda. The wave, however, is not
merely a movement of the basilar membrane, but an actual movement of
fluid or a transmission of pressure. As the one wave ascends while the
other descends, a pressure of the basilar membrane occurs at the point
where they meet; this causes the basilar membrane to move towards the
tectorial membrane, forcing this membrane suddenly against the apices
of the hair-cells, thus irritating the nerves. The point at which the
waves meet will depend on the time interval between the waves (Hurst,
"A New Theory of Hearing," _Trans. Biol. Soc. Liverpool_, 1895, vol.
ix. p. 321). More recently Max Mayer has advanced a theory somewhat
similar. He supposes that with each movement of the stapes
corresponding to a vibration, a wave travels up the scala vestibuli,
pressing the basilar membrane downwards. As it meets with resistance
in passing upwards, its amplitude therefore diminishes, and in this
way the distance up the scala through which the wave progresses will
be determined by its amplitude. The wave in its progress irritates a
certain number of nerve terminations, consequently feeble tones will
irritate only those nerve fibres that are near the fenestra ovalis,
while stronger tones will pass farther up and irritate a larger number
of nerve fibres the same number of times per unit of time. Pitch,
according to this view, depends on the number of stimuli per second,
while loudness depends on the number of nerve fibres irritated. Mayer
also applies the theory to the explanation of the powers of the
cochlea as an analyser, by supposing that with a compound tone these
are at maxima and minima of stimulation. As the compound wave travels
up the scala, portions of the wave corresponding to maxima and minima
die away in consecutive series, until only a maximum and minimum are
left; and, finally, as the wave travels farther, these also disappear.
With each maximum and minimum different parts of the basilar membrane
are affected, and affected a different number of times per second,
according to the frequencies of the partials existing in the compound
tone. Thus with a fifth, 2 : 3, there are three maxima and three
minima; but the compound tone is resolved into three tones having
vibration frequencies in the ratio of 3 : 2 : 1. According to Mayer,
we actually hear when a fifth is sounded tones of the relationship of
3 : 2 : 1, the last (1) being the differential tone. He holds, also,
that combinational tones are entirely subjective (Max Mayer, _Ztschr.
f. Psych. und Phys. d. Sinnesorgane_, Leipzig, Bd. xvi. and xvii.;
also _Verhandl. d. physiolog. Gesellsch. zu Berlin_, Feb. 18, 1898, S.
49). Two fatal objections can be urged to these theories, namely,
first, it is impossible to conceive of minute waves following each
other in rapid succession in the minute tubes forming the scalae--the
length of the scala being only a very small part of the wave-length of
the sound; and, secondly, neither theory takes into account the
differentiation of structure found in the epithelium of the organ of
Corti. Each push in and out of the base of the stapes must cause a
movement of the fluid, or a pressure, in the scalae as a whole.
There are difficulties in the way of applying the resonance theory to
the perception of noises. Noises have pitch, and also each noise has a
special character; if so, if the noise is analysed into its
constituents, why is it that it seems impossible to analyse a noise,
or to perceive any musical element in it? Helmholtz assumed that a
sound is noisy when the wave is irregular in rhythm, and he suggested
that the crista and macula acustica, structures that exist not in the
cochlea but in the vestibule, have to do with the perception of noise.
These structures, however, are concerned rather in the sense of the
perception of equilibrium than of sound (see EQUILIBRIUM).
9. Hitherto we have considered only the audition of a single sound,
but it is possible also to have simultaneous auditive sensations, as
in musical harmony. It is difficult to ascertain what is the limit
beyond which distinct auditory sensations may be perceived. We have in
listening to an orchestra a multiplicity of sensations which produces
a total effect, while, at the same time, we can with ease single out
and notice attentively the tones of one or two special instruments.
Thus the pleasure of music may arise partly from listening to
simultaneous, and partly from the effect of contrast or suggestion in
passing through successive, auditory sensations.
The principles of harmony belong to the subject of music (see
HARMONY), but it is necessary here briefly to refer to these from the
physiological point of view. If two musical sounds reach the ear at
the same moment, an agreeable or disagreeable sensation is
experienced, which may be termed a _concord_ or a _discord_, and it
can be shown by experiment with the syren that this depends upon the
vibrational numbers of the two tones. The octave (1 : 2), the twelfth
(1 : 3) and double octave (1 : 4) are absolutely consonant sounds; the
fifth (2 : 3) is said to be perfectly consonant; then follow, in the
direction of dissonance, the fourth (3 : 4), major sixth (3 : 5),
major third (4 : 5), minor sixth (5 : 8) and the minor third (5 : 6).
Helmholtz has attempted to account for this by the application of his
theory of _beats_.
Beats are observed when two sounds of nearly the same pitch are
produced together, and the number of beats per second is equal to the
difference of the number of vibrations of the two sounds. Beats give
rise to a peculiarly disagreeable intermittent sensation. The maximum
roughness of beats is attained by 33 per second; beyond 132 per
second, the individual impulses are blended into one uniform auditory
sensation. When two notes are sounded, say on a piano, not only may
the first, fundamental or prime tones beat, but partial tones of each
of the primaries may beat also, and as the difference of pitch of two
simultaneous sounds augments, the number of beats, both of prime tones
and of harmonics, augments also. The physiological effect of beats,
though these may not be individually distinguishable, is to give
roughness to the ear. If harmonics or partial tones of prime tones
coincide, there are no beats; if they do not coincide, the beats
produced will give a character of roughness to the interval. Thus in
the octave and twelfth, all the partial tones of the acute sound
coincide with the partial tones of the grave sound; in the fourth,
major sixth and major third, only two pairs of the partial tones
coincide, while in the minor sixth, minor third and minor seventh only
one pair of the harmonics coincide.
It is possible by means of beats to measure the sensitiveness of the
ear by determining the smallest difference in pitch that may give rise
to a beat. In no part of the scale can a difference smaller than 0.2
vibration per second be distinguished. The sensitiveness varies with
pitch. Thus at 120 vibs. per second 0.4 vib. per second, at 500 about
0.3 vib. per second, and at 1000, 0.5 vib. per second can be
distinguished. This is a remarkable illustration of the sensitiveness
of the ear. When tones of low pitch are produced that do not rapidly
die away, as by sounding heavy tuning-forks, not only may the beats be
perceived corresponding to the difference between the frequencies of
the forks, but also other sets of beats. Thus, if the two tones have
frequencies of 40 and 74, a two-order beat may be heard, one having a
frequency of 34 and the other of 6, as 74 / 40 = 1 + a positive
remainder of 34, and 74 / 40 = 2 - 6, or 80 - 74, a negative remainder
of 6. The lower beat is heard most distinctly when the number is less
than half the frequency of the lower primary, and the upper when the
number is greater. The beats we have been considering are produced
when two notes are sounded slightly differing in frequency, or at all
events their frequencies are not so great as those of two notes
separated by a musical interval, such as an octave or a fifth. But
Lord Kelvin has shown that beats may also be produced on slightly
inharmonious musical intervals (_Proc. Roy. Soc. Ed._ 1878, vol. ix.
p. 602). Thus, take two tuning-forks, ut2 = 256 and ut3 = 512;
slightly flatten ut3 so as to make its frequency 510, and we hear, not
a roughness corresponding to 254 beats, but a slow beat of 2 per
second. The sensation also passes through a cycle, the beats now
sounding loudly and fading away in intensity, again sounding loudly,
and so on. One might suppose that the beat occurred between 510 (the
frequency of ut3 flattened) and 512, the first partial of ut2, namely
ut3, but this is not so, as the beat is most audible when ut2 is
sounded feebly. In a similar way, beats may be produced on the
approximate harmonies 2 : 3, 3 : 4, 4 : 5, 5 : 6, 6 : 7, 7 : 8, 1 : 3,
3 : 5, and beats may even be produced on the major chord 4 : 5 : 6 by
sounding ut3, mi3, sol3, with sol3 or mi3 slightly flattened, "when a
peculiar beat will be heard as if a wheel were being turned against a
surface, one small part of which was rougher than the rest." These
beats on imperfect harmonies appear to indicate that the ear does
distinguish between an increase of pressure on the drum-head and a
diminution, or between a push and a pull, or, in other words, that it
is affected by phase. This was denied by Helmholtz.
10. _Beat Tones._--Considerable difference of opinion exists as to
whether beats can blend so as to give a sensation of tone; but R.
Konig, by using pure tones of high pitch, has settled the question.
These tones were produced by large tuning-forks. Thus ut6 = 2048 and
re6 = 2304. Then the beat tone is ut3 = 256 (2304-2048). If we strike
the two forks, ut3 sounds as a grave or lower beat tone. Again, ut6 =
2048 and si6 = 3840. Then (2048)2 - 3840 = 256, a negative remainder,
ut3, as before, and when both forks are sounded ut3 will be heard.
Again, ut6 = 2048 and sol6 = 3072, and 3072 - 2048 = 1024, or ut6,
which will be distinctly heard when ut6 and sol6 are sounded (Konig,
_Quelques experiences d'acoustique_, Paris, 1882, p. 87).
11. _Combination Tones._--Frequently, when two tones are sounded, not
only do we hear the compound sound, from which we can pick out the
constituent tones, but we may hear other tones, one of which is lower
in pitch than the lowest primary, and the other is higher in pitch
than the higher primary. These, known as combination tones, are of two
classes: _differential_ tones, in which the frequency is the
difference of the frequencies of the generating tones, and
_summational_ tones, having a frequency which is the sum of the
frequencies of the tones producing them. Differential tones, first
noticed by Sorge about 1740, are easily heard. Thus an interval of a
fifth, 2 : 3, gives a differential tone 1, that is, an octave below 2;
a fourth, 3 : 4, gives 1, a twelfth below 3; a major third, 4 : 5,
gives 1, two octaves below 4; a minor third, 5 : 6, gives 1, two
octaves and a major third below 5; a major sixth, 3 : 5, gives 2, that
is, a fifth below 3; and a minor sixth, 5 : 8, gives 3, that is, a
major sixth below 5. Summational tones, first noticed by Helmholtz,
are so difficult to hear that much controversy has taken place as to
their very existence. Some have contended that they are produced by
beats. It appears to be proved physically that they may exist in the
air outside of the ear. Further differential tones may be generated in
the middle ear. Helmholtz also demonstrated their independent
existence, and he states that "whenever the vibrations of the air or
of other elastic bodies, which are set in motion at the same time by
two generating simple tones, are so powerful that they can no longer
be considered infinitely small, mathematical theory shows that
vibrations of the air must arise which have the same vibrational
numbers as the combination tones" (Helmholtz, _Sensations of Tone_, p.
235). The importance of these combinational tones in the theory of
hearing is obvious. If the ear can only analyse compound waves into
simple pendular vibrations of a certain order (simple multiples of the
prime tone), how can it detect combinational tones, which do not
belong to that order? Again, if such tones are purely subjective and
only exist in the mind of the listener, the fact would be fatal to the
resonance theory. There can be no doubt, however, that the ear, in
dealing with them, vibrates in some part of its mechanism with each
generator, while it also is affected by the combinational tone itself,
according to its frequency.
12. Hearing with two ears does not appear materially to influence
auditive sensation, but probably the two organs are enabled, not only
to correct each other's errors, but also to aid us in determining the
locality in which a sound originates. It is asserted by G. T. Fechner
that one ear may perceive the same tone at a slightly higher pitch
than the other, but this may probably be due to some slight
pathological condition in one ear. If two tones, produced by two
tuning-forks, of equal pitch, are produced one near each ear, there is
a uniform single sensation; if one of the tuning-forks be made to
revolve round its axis in such a way that its tone increases and
diminishes in intensity, neither fork is heard continuously, but both
sound alternately, the fixed one being only audible when the revolving
one is not. It is difficult to decide whether excitations of
corresponding elements in the two ears can be distinguished from each
other. It is probable that the resulting sensations may be
distinguished, provided one of the generating tones differs from the
other in intensity or quality, although it may be the same in pitch.
Our judgment as to the direction of sounds is formed mainly from the
different degrees of intensity with which they are heard by two ears.
Lord Rayleigh states that diffraction of the sound-waves will occur as
they pass round the head to the ear farthest from the source of sound;
thus partial tones will reach the two ears with different intensities,
and thus quality of tone may be affected (_Trans. Music. Soc._,
London, 1876). Silvanus P. Thompson advocates a similar view, and he
shows that the direction of a complex tone can be more accurately
determined than the direction of a simple tone, especially if it be of
low pitch (_Phil. Mag._, 1882). (J. G. M.)
HEARN, LAFCADIO (1850-1904), author of books about Japan, was born on
the 27th of June 1850 in Leucadia (pronounced Lefcadia, whence his name,
which was one adopted by himself), one of the Greek Ionian Islands. He
was the son of Surgeon-major Charles Hearn, of King's County, Ireland,
who, during the English occupation of the Ionian Islands, was stationed
there, and who married a Greek wife. Artistic and rather bohemian tastes
were in Lafcadio Hearn's blood. His father's brother Richard was at one
time a well-known member of the Barbizon set of artists, though he made
no mark as a painter through his lack of energy. Young Hearn had rather
a casual education, but was for a time (1865) at Ushaw Roman Catholic
College, Durham. The religious faith in which he was brought up was,
however, soon lost; and at nineteen, being thrown on his own resources,
he went to America and at first picked up a living in the lower grades
of newspaper work. The details are obscure, but he continued to occupy
himself with journalism and with out-of-the-way observation and reading,
and meanwhile his erratic, romantic and rather morbid idiosyncrasies
developed. He was for some time in New Orleans, writing for the _Times
Democrat_, and was sent by that paper for two years as correspondent to
the West Indies, where he gathered material for his _Two Years in the
French West Indies_ (1890). At last, in 1891, he went to Japan with a
commission as a newspaper correspondent, which was quickly broken off.
But here he found his true sphere. The list of his books on Japanese
subjects tells its own tale: _Glimpses of Unfamiliar Japan_ (1894); _Out
of the East_ (1895); _Kokoro_ (1896); _Gleanings in Buddha Fields_
(1897); _Exotics and Retrospections_ (1898); _In Ghostly Japan_ (1899);
_Shadowings_ (1900); _A Japanese Miscellany_ (1901); _Kotto_ (1902);
_Japanese Fairy Tales_ and _Kwaidan_ (1903), and (published just after
his death) _Japan, an Attempt at Interpretation_ (1904), a study full of
knowledge and insight. He became a teacher of English at the University
of Tokyo, and soon fell completely under the spell of Japanese ideas. He
married a Japanese wife, became a naturalized Japanese under the name of
Yakumo Koizumi, and adopted the Buddhist religion. For the last two
years of his life (he died on the 26th of September 1904) his health was
failing, and he was deprived of his lecturersbip at the University. But
he had gradually become known to the world at large by the originality,
power and literary charm of his writings. This wayward bohemian genius,
who had seen life in so many climes, and turned from Roman Catholic to
atheist and then to Buddhist, was curiously qualified, among all those
who were "interpreting" the new and the old Japan to the Western world,
to see it with unfettered understanding, and to express its life and
thought with most intimate and most artistic sincerity. Lafcadio Hearn's
books were indeed unique for their day in the literature about Japan, in
their combination of real knowledge with a literary art which is often
exquisite.
See Elizabeth Bisland, _The Life and Letters of Lafcadio Hearn_ (2
vols., 1906); G. M. Gould, _Concerning Lafcadio Hearn_ (1908).
HEARNE, SAMUEL (1745-1792), English explorer, was born in London. In
1756 he entered the navy, and was some time with Lord Hood; at the end
of the Seven Years' War (1763) he took service with the Hudson's Bay
Company. In 1768 he examined portions of the Hudson's Bay coasts with a
view to improving the cod fishery, and in 1769-1772 he was employed in
north-western discovery, searching especially for certain copper mines
described by Indians. His first attempt (from the 6th of November 1769)
failed through the desertion of his Indians; his second (from the 23rd
of February 1770) through the breaking of his quadrant; but in his third
(December 1770 to June 1772) he was successful, not only discovering the
copper of the Coppermine river basin, but tracing this river to the
Arctic Ocean. He reappeared at Fort Prince of Wales on the 30th of June
1772. Becoming governor of this fort in 1775, he was taken prisoner by
the French under La Perouse in 1782. He returned to England in 1787 and
died there in 1792.
See his posthumous _Journey from Prince of Wales Fort in Hudson's Bay
to the Northern Ocean_ (London, 1795).
HEARNE, THOMAS (1678-1735), English antiquary, was born in July 1678 at
Littlefield Green in the parish of White Waltham, Berkshire. Having
received his early education from his father, George Hearne, the parish
clerk, he showed such taste for study that a wealthy neighbour, Francis
Cherry of Shottesbrooke (c. 1665-1713), a celebrated nonjuror,
interested himself in the boy, and sent him to the school at Bray "on
purpose to learn the Latin tongue." Soon Cherry took him into his own
house, and his education was continued at Bray until Easter 1696, when
he matriculated at St Edmund Hall, Oxford. At the university he
attracted the attention of Dr John Mill (1645-1707), the principal of St
Edmund Hall, who employed him to compare manuscripts and in other ways.
Having taken the degree of B.A. in 1699 he was made assistant keeper of
the Bodleian Library, where he worked on the catalogue of books, and in
1712 he was appointed second keeper. In 1715 Hearne was elected
architypographus and esquire bedell in civil law in the university, but
objection having been made to his holding this office together with that
of second librarian, he resigned it in the same year. As a nonjuror he
refused to take the oaths of allegiance to King George I., and early in
1716 he was deprived of his librarianship. However he continued to
reside in Oxford, and occupied himself in editing the English
chroniclers. Having refused several important academical positions,
including the librarianship of the Bodleian and the Camden professorship
of ancient history, rather than take the oaths, he died on the 10th of
June 1735.
Hearne's most important work was done as editor of many of the English
chroniclers, and until the appearance of the "Rolls" series his
editions were in many cases the only ones extant. Very carefully
prepared, they were, and indeed are still, of the greatest value to
historical students. Perhaps the most important of a long list are:
Benedict of Peterborough's (Benedictus Abbas) _De vita et gestis
Henrici II. et Ricardi I._ (1735); John of Fordun's _Scotichronicon_
(1722); the monk of Evesham's _Historia vitae et regni Ricardi II._
(1729); Robert Mannyng's translation of Peter Langtoft's _Chronicle_
(1725); the work of Thomas Otterbourne and John Whethamstede as _Duo
rerum Anglicarum scriptores veteres_ (1732); Robert of Gloucester's
_Chronicle_ (1724); J. Sprott's _Chronica_ (1719); the _Vita et gesta
Henrici V._, wrongly attributed to Thomas Elmham (1727); Titus Livy's
_Vita Henrici V._ (1716); Walter of Hemingburgh's _Chronicon_ (1731);
and William of Newburgh's _Historia rerum Anglicarum_ (1719). He also
edited John Leland's _Itinerary_ (1710-1712) and the same author's
_Collectanea_ (1715); W. Camden's _Annales rerum Anglicarum et
Hibernicarum regnante Elizabetha_ (1717); Sir John Spelman's _Life of
Alfred_ (1709); and W. Roper's _Life of Sir Thomas More_ (1716). He
brought out an edition of Livy (1708); one of Pliny's _Epistolae et
panegyricus_ (1703); and one of the Acts of the Apostles (1715). Among
his other compilations may be mentioned: _Ductor historicus, a Short
System of Universal History_ (1704, 1705, 1714, 1724); _A Collection
of Curious Discourses by Eminent Antiquaries_ (1720); and _Reliquiae
Bodleianae_ (1703).
Hearne left his manuscripts to William Bedford, who sold them to Dr
Richard Rawlinson, who in his turn bequeathed them to the Bodleian.
Two volumes of extracts from his voluminous diary were published by
Philip Bliss (Oxford, 1857), and afterwards an enlarged edition in
three volumes appeared (London, 1869). A large part of his diary
entitled _Remarks and Collections, 1705-1714_, edited by C. E. Doble
and D. W. Rannie, has been published by the Oxford Historical Society
(1885-1898). _Bibliotheca Hearniana_, excerpts from the catalogue of
Hearne's library, has been edited by B. Botfield (1848).
See _Impartial Memorials of the Life and Writings of Thomas Hearne by
several hands_ (1736); and W. D. Macray, _Annals of the Bodleian
Library_ (1890). Hearne's autobiography is published in W.
Huddesford's _Lives of Leland, Hearne and Wood_ (Oxford, 1772). T.
Ouvry's _Letters addressed to Thomas Hearne_ has been privately
printed (London, 1874).
HEARSE (an adaptation of Fr. _herse_, a harrow, from Lat. _hirpex_,
_hirpicem_, rake or harrow, Greek [Greek: arpae], a vehicle for the
conveyance of a dead body at a funeral. The most usual shape is a
four-wheeled car, with a roofed and enclosed body, sometimes with glass
panels, which contains the coffin. This is the only current use of the
word. In its earlier forms it is usually found as "herse," and meant, as
the French word did, a harrow (q.v.). It was then applied to other
objects resembling a harrow, following the French. It was then used of a
portcullis, and thus becomes a heraldic term, the "herse" being
frequently borne as a "charge," as in the arms of the City of
Westminster. The chief application of the word is, however, to various
objects used in funeral ceremonies. A "herse" or "hearse" seems first to
have been a barrow-shaped framework of wood, to hold lighted tapers and
decorations placed on a bier or coffin; this later developed into an
elaborate pagoda-shaped erection of woodwork or metal for the funerals
of royal or other distinguished persons. This held banners, candles,
armorial bearings and other heraldic devices. Complimentary verses or
epitaphs were often attached to the "hearse." An elaborate "hearse" was
designed by Inigo Jones for the funeral of James I. The "hearse" is also
found as a permanent erection over tombs. It is generally made of iron
or other metal, and was used, not only to carry lighted candles, but
also for the support of a pall during the funeral ceremony. There is a
brass "hearse" in the Beauchamp Chapel at Warwick Castle, and one over
the tomb of Robert Marmion and his wife at Tanfield Church near Ripon.
HEART, in anatomy.--The heart[1] is a four-chambered muscular bag, which
lies in the cavity of the thorax between the two lungs. It is surrounded
by another bag, the pericardium, for protective and lubricating purposes
(see COELOM AND SEROUS MEMBRANES). Externally the heart is somewhat
conical, its base being directed upward, backward and to the right, its
apex downward, forward and to the left. In transverse section the cone
is flattened, so that there is an anterior and a posterior surface and a
superior and inferior border. The superior border, running obliquely
downward and to the left, is very thick, and so gains the name of _margo
obtusus_, while the inferior border is horizontal and sharp and is
called _margo acutus_ (see fig. 1). The divisions between the four
chambers of the heart (namely, the two auricles and two ventricles) are
indicated on the surface by grooves, and when these are followed it will
be seen that the right auricle and ventricle lie on the front and right
side, while the left auricle and ventricle are behind and on the left.
[Illustration: FIG. 1. The Thoracic Viscera.--In this diagram the lungs
are turned to the side, and the pericardium removed to display the
heart, a, upper, a', lower lobe of left lung; b, upper, b', middle, b",
lower lobe of right lung; c, trachea; d, arch of aorta; e, superior vena
cava; f, pulmonary artery; g, left, and h, right auricle; k, right, and
l, left ventricle; m, inferior vena cava; n, descending aorta; 1,
innominate artery; 2, right, and 4, left common carotid artery; 3,
right, and 5, left subclavian artery; 6, 6, right and left innominate
vein; 7 and 9, left and right internal jugular veins; 8 and 10, left and
right subclavian veins; 11, 12, 13, left pulmonary artery, bronchus and
vein; 14, 15, 16, right pulmonary bronchus, artery and vein; 17 and 18,
left and right coronary arteries.]
The _right auricle_ is situated at the base of the heart, and its
outline is seen on looking at the organ from in front. Into the
posterior part of it open the two venae cavae (see fig. 2), the superior
(a) above and the inferior (b) below. In front and to the left of the
superior vena cava is the right auricular appendage (e) which overlaps
the front of the root of the aorta, while running obliquely from the
front of one vena cava to the other is a shallow groove called the
_sulcus terminalis_, which indicates the original separation between the
true auricle in front and the sinus venosus behind. When the auricle is
opened by turning the front wall to the right as a flap the following
structures are exposed:
[Illustration: FIG. 2. Cavities of the Right Side of the Heart.--a,
superior, and b, inferior vena cava; c, arch of aorta; d, pulmonary
artery; e, right, and f, left auricular appendage; g, fossa ovalis; h,
Eustachian valve; k, mouth of coronary vein; l, m, n, cusps of the
tricuspid valve; o, o, papillary muscles; p, semilunar valve; q, corpus
Arantii; r, lunula.]
1. A muscular ridge, called the _crista terminalis_, corresponding to
the sulcus terminalis on the exterior.
2. A series of ridges on the anterior wall and in the appendage, running
downward from the last and at right angles to it, like the teeth of a
comb; these are known as _Musculi pectinati_.
3. The orifice of the superior vena cava (fig. 2, a) at the upper and
back part of the chamber.
4. The orifice of the inferior vena cava (fig. 2, b) at the lower and
back part.
5. Attached to the right and lower margins of this opening are the
remains of the _Eustachian valve_ (fig. 2, h), which in the foetus
directs the blood from the inferior vena cava, through the _foramen
ovale_, into the left auricle.
6. Below and to the left of this is the opening of the _coronary sinus_
(fig. 2, k), which collects most of the veins returning blood from the
substance of the heart.
7. Guarding this opening is the _coronary valve_ or _valve of
Thebesius_.
8. On the posterior or septal wall, between the two auricles, is an oval
depression, called the _fossa ovalis_ (fig. 2, g), the remains of the
original communication between the two auricles. In about a quarter of
all normal hearts there is a small valvular communication between the
two auricles in the left margin of this depression (see "7th Report of
the Committee of Collective Investigation," _J. Anat. and Phys._ vol.
xxxii. p. 164).
9. The _annulus ovalis_ is the raised margin surrounding this
depression.
10. On the left side, opening into the right ventricle, is the _right
auriculo-ventricular opening_.
11. On the right wall, between the two caval openings, may occasionally
be seen a slight eminence, the _tubercle of Lower_, which is supposed to
separate the two streams of blood in the embryo.
12. Scattered all over the auricular wall are minute depressions, the
_foramina Thebesii_, some of which receive small veins from the
substance of the heart.
The _right ventricle_ is a triangular cavity (see fig. 2) the base of
which is largely formed by the auriculo-ventricular orifice. To the left
of this it is continued up into the root of the pulmonary artery, and
this part is known as the _infundibulum_. Its anterior wall forms part
of the anterior surface of the heart, while its posterior wall is
chiefly formed by the septum ventriculorum, between it and the left
ventricle. Its lower border is the margo acutus already mentioned. In
transverse section it is crescentic, since the septal wall bulges into
its cavity. In its interior the following structures are seen:
1. The _tricuspid valve_ (fig. 2, l, m, n) guarding against reflux of
blood into the right auricle. This consists of a short cylindrical
curtain of fibrous tissue, which projects into the ventricle from the
margin of the auriculo-ventricular aperture, while from its free edge
three triangular flaps hang down, the bases of which touch one another.
These cusps are spoken of as septal, marginal and infundibular, from
their position.
2. The _chordae tendineae_ are fine fibrous cords which fasten the cusps
to the musculi papillares and ventricular wall, and prevent the valve
being turned inside out when the ventricle contracts.
3. The _columnae carneae_ are fleshy columns, and are of three kinds.
The first are attached to the wall of the ventricle in their whole
length and are merely sculptured in relief, as it were; the second are
attached by both ends and are free in the middle; while the third are
known as the _musculi papillares_ and are attached by one end to the
ventricular wall, the other end giving attachment to the chordae
tendineae. These musculi papillares are grouped into three bundles (fig.
2, o).
4. The _moderator band_ is really one of the second kind of columnae
carneae which stretches from the septal to the anterior wall of the
ventricle.
5. The _pulmonary valve_ (fig. 2, p) at the opening of the pulmonary
artery has three crescentic, pocket-like cusps, which, when the
ventricle is filling, completely close the aperture, but during the
contraction of the ventricle fit into three small niches known as the
_sinuses of Valsalva_, and so are quite out of the way of the escaping
blood. In the middle of the free margin of each is a small knob called
the _corpus Arantii_ (fig. 2, q), and on each side of this a thin
crescent-shaped flap, the _lunula_ (fig. 2, r), which is only made of
two layers of endocardium, whereas in the rest of the cusp there is a
fibrous backing between these two layers.
The _left auricle_ is situated at the back of the base of the heart,
behind and to the left of the right auricle. Running down behind it are
the oesophagus and the thoracic aorta. When it is opened it is seen to
have a much lighter colour than the other cavities, owing to the greater
thickness of its endocardium obscuring the red muscle beneath. There are
no musculi pectinati except in the auricular appendage. The openings of
the four pulmonary veins are placed two on each side of the posterior
wall, but sometimes there may be three on the right side, and only one
on the left. On the septal wall is a small depression like the mark of a
finger-nail, which corresponds to the anterior part of the fossa ovalis
and often forms a valvular communication with the right auricle. The
auriculo-ventricular orifice is large and oval, and is directed downward
and to the left. Foramina Thebesii and venae minimae cordis are found in
this auricle, as in the right, although the chamber is one for arterial
or oxidized blood.
At the lower part of the posterior surface of the unopened auricle,
lying in the left auriculo-ventricular furrow, is the coronary sinus,
which receives most of the veins returning the blood from the heart
substance; these are the right and left coronary veins at each extremity
and the posterior and left cardiac veins from below. One small vein,
called the oblique vein of Marshall, runs down into it across the
posterior surface of the auricle, from below the left lower pulmonary
vein, and is of morphological interest.
The _left ventricle_ is conical, the base being above, behind and to the
right, while the apex corresponds to the apex of the heart and lies
opposite the fifth intercostal space, 3(1/2) in. from the mid line. The
following structures are seen inside it:--
1. The _mitral valve_ guarding the auriculo-ventricular opening has the
same arrangement as the tricuspid, already described, save that there
are only two cusps, named marginal and aortic, the latter of which is
the larger.
2. The chordae tendineae and columnae carneae resemble those of the
right ventricle, though there are only two bundles of musculi papillares
instead of three. These are very large. A moderator band has been found
as an abnormality (see _J. Anat. and Phys._ vol. xxx. p. 568).
3. The _aortic valve_ has the same structure as the pulmonary, though
the cusps are more massive. From the anterior and left posterior sinuses
of Valsalva the coronary arteries arise. That part of the ventricle just
below the aortic valve, corresponding to the infundibulum on the right,
is known as the aortic vestibule.
The walls of the left ventricle are three times as thick as those of the
right, except at the apex, where they are thinner. The septum
ventriculorum is concave towards the left ventricle, so that a
transverse section of that cavity is nearly circular. The greater part
of it has nearly the same thickness as the rest of the left ventricular
wall and is muscular, but a small portion of the upper part is
membranous and thin, and is called the _pars membranacea septi_; it lies
between the aortic and pulmonary orifices.
_Structure of the Heart._--The arrangement of the muscular fibres of the
heart is very complicated and only imperfectly known. For details one of
the larger manuals, such as Cunningham's _Anatomy_ (London, 1910), or
Gray's _Anatomy_ (London, 1909), should be consulted. The general scheme
is that there are superficial fibres common to the two auricles and two
ventricles and deeper fibres for each cavity. Until recently no fibres
had been traced from the auricles to the ventricles, though Gaskell
predicted that these would be found, and the credit for first
demonstrating them is due to Stanley Kent, their details having
subsequently been worked out by W. His, Junr., and S. Tawara. The fibres
of this _auriculo-ventricular bundle_ begin, in the right auricle, below
the opening of the coronary sinus, and run forward on the right side of
the auricular septum, below the fossa ovalis, and close to the
auriculo-ventricular septum. Above the septal flap of the tricuspid
valve they thicken and divide into two main branches, one on either side
of the ventricular septum, which run down to the bases of the anterior
and posterior papillary muscles, and so reach the walls of the
ventricle, where their secondary branches form the _fibres of Purkinje_.
The bundle is best seen in the hearts of young Ruminants, and it is
presumably through it that the wave of contraction passes from the
auricles to the ventricles (see article by A. Keith and M. Flack,
_Lancet_, 11th of August 1906, p. 359).
The _central fibrous body_ is a triangular mass of fibro-cartilage,
situated between the two auriculo-ventricular and the aortic orifices.
The upper part of the septum ventriculorum blends with it. The
_endocardium_ is a delicate layer of endothelial cells backed by a very
thin layer of fibro-elastic tissue; it is continuous with the
endothelium of the great vessels and lines the whole of the cavities of
the heart.
The heart is roughly about the size of the closed fist and weighs from 8
to 12 oz.; it continues to increase in size up to about fifty years of
age, but the increase is more marked in the male than in the female.
Each ventricle holds about 4 f. oz. of blood, and each auricle rather
less. The nerves of the heart are derived from the vagus, spinal
accessory and sympathetic, through the superficial and deep cardiac
plexuses.
_Embryology._
In the article on the arteries (q.v.) the formation and coalescence of
the two _primitive ventral aortae_ to form the heart are noticed, so
that we may here start with a straight median tube lying ventral to the
pharynx and being prolonged cephalad into the ventral aortae and caudad
into the vitelline veins. This soon shows four dilatations, which, from
the tail towards the head end, are called the sinus venosus, the
auricle, the ventricle and the truncus[2] arteriosus. As the tubular
heart grows more rapidly than the pericardium which contains it, it
becomes bent into the form of an S laid on its side ([rotated S]), the
ventral convexity being the ventricle and the dorsal the auricle. The
passage from the auricle to the ventricle is known as the _auricular
canal_, and in the dorsal and ventral parts of this appear two
thickenings known as _endocardial cushions_, which approach one another
and leave a transverse slit between them (fig. 3, E.C.). Eventually
these two cushions fuse in the middle line, obliterating the central
part of the slit, while the lateral parts remain as the two
auriculo-ventricular orifices; this fusion is known as the _septum
intermedium_. From the bottom (ventral convexity) of the ventricle an
antero-posterior median septum grows up, which is the _septum inferius_
or _septum ventriculorum_ (fig. 3, V). Posteriorly (caudally) this
septum fuses with the septum intermedium, but anteriorly it is free at
the lower part of the truncus arteriosus. On referring to the
development of the arteries (see ARTERIES) it will be seen that another
septum starts between the last two pairs of aortic arches and grows
downward (caudad) until it reaches and joins with the septum inferius
just mentioned. This _septum aorticum_ (formed by two ingrowths from the
wall of the vessel which fuse later) becomes twisted in such a way that
the right ventricle is continuous with the last pair of aortic arches
(pulmonary artery), while the left ventricle communicates with the other
arches (the permanent ventral aorta and its branches); it joins the
septum ventriculorum in the upper part of the ventricular cavity and so
forms the _pars membranacea septi_ (fig. 3, T. Ar).
[Illustration: FIG. 3.--Formation of Septa. Diagram of the formation of
some of the septa of the heart (viewed from the right side).
S.V. Sinus venosus.
Au. Auricle.
E.C. Endocardial cushions forming septum intermedium.
V. Septum ventriculorum.
T. Ar. Septum aorticum intruncus arteriosus.
V.A. Ventral aorta.]
The fate of the sinus venosus and auricle must now be followed. Into the
former, at first, only the two vitelline veins open, but later, as they
develop, the _ducts of Cuvier_ and the _umbilical veins_ join in (see
VEINS). As the ducts of Cuvier come from each side the sinus spreads out
to meet them and becomes transversely elongated. The slight
constriction, which at first is the only separation between the sinus
and the auricle, becomes more marked, and later the opening is into the
right part of the auricle, and is guarded by two valvular folds of
endocardium (the _venous valves_) which project into that cavity, and
are continuous above with a temporary downgrowth from the roof, known as
the _septum spurium_. Later the right side of the sinus enlarges, and so
does the right part of the aperture, until the back part of the right
side of the auricle and the right part of the sinus venosus are thrown
into one, and the only remnants of the partition are the crista
terminalis and the Eustachian and Thebesian Valves. The left part of the
sinus venosus, which does not enlarge at the same rate as the right
part, remains as the coronary sinus. It will now be seen why, in the
adult heart, all the veins which open into the right auricle open into
its posterior part, behind the crista terminalis. The septum spurium has
been referred to as a temporary structure; the real division between the
two auricles occurs at a later date than that between the ventricles and
to the left of the septum spurium. It is formed by two partitions, the
first of which, called the _septum primum_, grows down from the
auricular roof. At first it does not quite reach the endocardial
cushions in the auricular canal, already mentioned, but leaves a gap,
called the _ostium primum_, between. This has nothing to do with the
_foramen ovale_, which occurs as an independent perforation higher up,
and at first is known as the _ostium secundum_. When it is established
the septum primum grows down and meets the endocardial cushions, and so
the ostium primum is obliterated. The _septum secundum_ grows down on
the right of the septum primum and is never complete; it grows round and
largely overlaps the foramen ovale and its edges form the annulus
ovalis, so that, in the later months of foetal life, the foramen ovale
is a valvular opening, the floor of which is formed by the septum primum
and the margins by the septum secundum. The closure of the foramen is
brought about by adhesion of the two septa.
The pulmonary veins of the two sides at first join one another, dorsal
to the left auricle, and open into that cavity by a single median trunk,
but, as the auricle grows, this trunk and part of the right and left
veins are absorbed into its cavity.
The mitral and tricuspid valves are formed by the shortening of the
auricular canal which becomes telescoped into the ventricle, and the
cusps are the remnants of this telescoping process.
The columnae carneae and chordae tendineae are the remains of a spongy
network which originally filled the cavity of the primary ventricle.
The aortic and pulmonary valves are laid down in the ventral aorta,
before it is divided into aorta and pulmonary artery, as four
endocardial cushions; anterior, posterior and two lateral. The septum
aorticum cuts the latter two into two, so that each artery has the
rudiments of three cusps.
Abnormalities of the heart are very numerous, and can usually be
explained by a knowledge of its development. They often cause grave
clinical symptoms. A clear and well-illustrated review of the most
important of them will be found in the chapter on congenital disease of
the heart in _Clinical Applied Anatomy_, by C. R. Box and W. McAdam
Eccles, London, 1906.
For further details of the embryology of the heart see Oscar Hertwig's
_Entwicklungslehre der Wirbeltiere_ (Jena, 1902); G. Born,
"Entwicklung des Saugetierherzens," _Archiv f. mik. Anat._ Bd. 33
(1889); W. His, _Anatomie menschlicher Embryonen_ (Leipzig,
1881-1885); Quain's _Anatomy_, vol. i. (1908); C. S. Minot, _Human
Embryology_ (New York, 1892); and A. Keith, _Human Embryology and
Morphology_ (London, 1905).
_Comparative Anatomy._
In the Acrania (e.g. lancelet) there is no heart, though the vessels are
specially contractile in the ventral part of the pharynx.
In the Cyclostomata (lamprey and hag), and Fishes, the heart has the same
arrangement which has been noticed in the human embryo. There is a smooth,
thin-walled sinus venosus, a thin reticulate-walled auricle, produced
laterally into two appendages, a thick-walled ventricle, and a _conus
arteriosus_ containing valves. In addition to these the beginning of the
ventral aorta is often thickened and expanded to form a _bulbus
arteriosus_, which is non-contractile, and, strictly speaking, should
rather be described with the arteries than with the heart. In relation to
human embryology the smooth sinus venosus and reticulated auricle are
interesting. Between the auricle and ventricle is the auriculo-ventricular
valve, which primarily consists of two cusps, comparable to the two
endocardial cushions of the human embryo, though in some forms they may be
subdivided. In the interior of the ventricle is a network of muscular
trabeculae. The conus arteriosus in the Elasmobranchs (sharks and rays)
and Ganoids (sturgeon) is large and provided with several rows of
semilunar valves, but in the Cyclostomes (lamprey) and Teleosts (bony
fishes) the conus is reduced and only the anterior (cephalic) row of
valves retained. With the reduction of the conus the bulbus arteriosus is
enlarged. So far the heart is a single tubular organ expanded into various
cavities and having the characteristic [rotated S]-shaped form seen in the
human embryo; it contains only venous blood which is forced through the
gills to be oxidized on its way to the tissues. In the Dipnoi (mud fish),
in which rudimentary lungs, as well as gills, are developed, the auricle
is divided into two, and the sinus venosus opens into the right auricle.
The conus arteriosus too begins to be divided into two chambers, and in
Protopterus this division is complete. This division of the heart is one
instance in which mammalian ontogeny does not repeat the processes of
phylogeny, because, in the human embryo, it has been shown that the
ventricular septum appears before the auricular. This want of harmony is
sometimes spoken of as the "falsification of the embryological record."
In the Amphibia there are also two auricles and one ventricle, though in
the Urodela (tailed amphibians) the auricular septum is often
fenestrated. The sinus venosus is still a separate chamber, and the
conus arteriosus, which may contain many or few valves, is usually
divided into two by a spiral fold. Structurally the amphibian heart
closely resembles the dipnoan, though the increased size of the left
auricle is an advance. In the Anura (frogs and toads) the whole
ventricle is filled with a spongy network which prevents the arterial
and venous blood from the two auricles mixing to any great extent. (For
the anatomy and physiology of the frog's heart, see _The Frog_, by
Milnes Marshall.)
In the Reptiles the ventricular septum begins to appear; this in the
lizards is quite incomplete, but in the crocodiles, which are usually
regarded as the highest order of living reptiles, the partition has
nearly reached the top of the ventricle, and the condition resembles
that of the human embryo before the pars membranacea septi is formed.
The conus arteriosus becomes included in the ventricular cavity, but the
sinus venosus still remains distinct, and its opening into the right
ventricle is guarded by two valves which closely resemble the two venous
valves in the auricle of the human embryo already referred to.
In the Birds the auricular and ventricular septa are complete; the right
ventricle is thin-walled and crescentic in section, as in Man, and the
musculi papillares are developed. The left auriculo-ventricular valve
has three membranous cusps with chordae tendineae attached to them, but
the right auriculo-ventricular valve has a large fleshy cusp without
chordae tendineae. The sinus venosus is largely included in the right
auricle, but remains of the two venous valves are seen on each side of
the orifice of the inferior vena cava.
In the Mammals the structure of the heart corresponds closely with the
description of that of Man already given. In the Ornithorynchus, among
the Monotremes, the right auriculo-ventricular valve has two fleshy and
two membranous cusps, thus showing a resemblance to that of the bird. In
the Echidna, the other member of the order, however, both
auriculo-ventricular valves are membranous. In the Edentates the remains
of the venous valves at the opening of the inferior vena cava are better
marked than in other orders. In the Ungulates the moderator band in the
right ventricle is especially well developed, and the central fibrous
body at the base of the heart is often ossified, forming the os cordis
so well known in the heart of the ox.
The position of the heart in the lower mammals is not so oblique as it
is in Man.
For further details, see C. Rose, _Beitr. z. vergl. Anal. des Herzens
der Wirbelthiere Morph. Jahrb._, Bd. xvi. (1890); R. Wiedersheim,
_Vergleichende Anatomie der Wirbelthiere_ (Jena, 1902) (for
literature); also Parker and Haswell's _Zoology_ (London, 1897).
(F. G. P.)
HEART DISEASE.--In the early ages of medicine, the absence of correct
anatomical, physiological and pathological knowledge prevented diseases
of the heart from being recognized with any certainty during life, and
almost entirely precluded them from becoming the object of medical
treatment. But no sooner did Harvey (1628) publish his discovery of the
circulation of the blood, and its dependence on the heart as its central
organ, than derangements of the circulation began to be recognized as
signs of disease of that central organ. (See also under VASCULAR
SYSTEM.)
Among the earliest to profit by this discovery and to make important
contributions to the literature of diseases of the heart and circulation
were, R. Lower (1631-1691), R. Vieussens (1641-1716). H. Boerhave
(1668-1738) and the great pathologists at the beginning of the 18th
century, G. M. Lancisi (1654-1720), G. B. Morgagni (1682-1771) and J. B.
Senac (1693-1770). The works of these writers form very interesting
reading, and it is remarkable how careful were the observations made,
and how sound the conclusions drawn, by these pioneers of scientific
medicine. J. N. Corvisart (1755-1821) was one of the earliest to make
practical use of R. T. Auenbrugger's (1722-1809) invention of percussion
to determine the size of the heart. R. T. H. Laennec (1781-1826) was the
first to make a scientific application of mediate auscultation to the
diagnosis of disease of the chest, by the invention of the stethoscope.
J. Bouillaud (1796-1881) extended its use to the diagnosis of disease of
the heart. To James Hope (1801-1841) we owe much of the precision we
have now attained in diagnosis of valvular disease from abnormalities in
the sounds produced during cardiac movements. This short list by no
means exhausts the earlier literature on the subject, but each of these
names marks an era in the progress of the diagnosis of cardiac disease.
In later years the literature on this subject has become very copious.
The heart and great vessels occupy a position immediately to the left of
the centre of the thoracic cavity. The anterior surface of the heart is
projected against the chest wall and is surrounded on either side by the
lungs, which are resonant organs, so that any increase in the size of
the heart, "dilatation," can be detected by percussion. By placing the
hand on the chest, palpation, the impulse of the left ventricle, or apex
beat, can normally be felt just below and internal to the nipple.
Deviations from the normal in the position or force of the apex beat
will afford important information as to the nature of the pathological
changes in the heart. Thus, displacement downwards and outwards of the
apex beat, with a forcible thrusting impulse, will indicate hypertrophy,
or increase of the muscular wall and increased driving power of the left
ventricle, whereas a similar displacement with a feeble diffuse impulse
will indicate dilatation, or over-distension of its cavity from
stretching of the walls.
By auscultation, or listening with a suitable instrument named a
stethoscope over appropriate areas, we can detect any abnormality in the
sounds of the heart, and the presence of murmurs indicative of disease
of one or other of the valves of the heart.
The pericardium is a fibro-serous sac which loosely envelops the heart
and the origin of the great vessels. Inflammation of this sac, or
_pericarditis_, is apt to occur as a result of rheumatism, more
especially in children. It may also occur as a complication of
pneumonia. It is a serious affection associated with pain over the
heart, fever, shortness of breath, rapid pulse and dilatation of the
heart. As a result of the inflammation, fluid may accumulate in the
pericardial sac, or the walls of the sac may become adherent to the
heart and tend to embarrass its action. In favourable cases, however,
recovery may take place without any untoward sequelae.
Diseases of the heart may be classified in two main groups, (1) Disease
of the valves, and (2) Disease of the walls of the heart.
1. _Valvular Disease._--Inflammation of the valves of the heart, or
_endocarditis_, is one of the most common complications of rheumatism in
children and young adults. More severe types, which are apt to prove
fatal from a form of blood poisoning, may result when the valves of the
heart are attacked by certain micro-organisms, such as the pneumococcus,
which is responsible for pneumonia, the streptococcus and the
staphylococcus pyogenes, the gonococcus and the influenza bacillus.
As a result of endocarditis, one or more of the valves may be seriously
damaged, so that it leaks or becomes incompetent. The valves of the left
side of the heart, the aortic and mitral valves, are affected far more
commonly than those of the right side. It is indeed comparatively rarely
that the latter are attacked. In the process of healing of a damaged
valve, scar tissue is formed which has a tendency to contract, so that
in some cases the orifice of the valve becomes narrowed, and the
resulting stenosis or narrowing gives rise to obstruction of the blood
stream. We may thus have incompetence or stenosis of a valve or both
combined.
Valvular lesions are detected on auscultation over appropriate areas by
the blowing sounds or murmurs to which they give rise, which modify or
replace the normal heart sounds. Thus, lesions of the mitral valve give
rise to murmurs which are heard at the apex beat of the heart, and
lesions of the aortic valves to murmurs which are heard over the aortic
area, in the second right intercostal space. Accurate timing of the
murmurs in relation to the heart sounds enables us to judge whether the
murmur is due to stenosis or incompetence of the valve affected.
If the valvular lesion is severe, it is essential for the proper
maintenance of the circulation that certain changes should take place in
the heart to compensate for or neutralize the effects of the
regurgitation or obstruction, as the case may be. In affections of the
aortic valve, the extra work falls on the left ventricle, which enlarges
proportionately and undergoes hypertrophy. In affections of the mitral
valve the effect is felt primarily by the left auricle, which is a thin
walled structure incapable of undergoing the requisite increase in power
to resist the backward flow through the mitral orifice in case of
leakage, or to overcome the effects of obstruction in case of stenosis.
The back pressure is therefore transmitted to the pulmonary circulation,
and as the right ventricle is responsible for maintaining the flow of
blood through the lungs, the strain and extra work fall on the right
ventricle, which in turn enlarges and undergoes hypertrophy. The degree
of hypertrophy of the left or right ventricle is thus, up to a certain
point, a measure of the extent of the lesion of the aortic or mitral
valve respectively. When the effects of the valvular lesion are so
neutralized by these structural changes in the heart that the
circulation is equably maintained, "compensation" is said to be
efficient.
When the heart gives way under the strain, compensation is said to break
down, and dropsy, shortness of breath, cough and cyanosis, are among the
distressing symptoms which may set in. The mere existence of a valvular
lesion does not call for any special treatment so long as compensation
is efficient, and a large number of people with slight valvular lesions
are living lives indistinguishable from those of their neighbours. It
will, however, be readily understood that in the case of the more
serious lesions certain precautions should be observed in regard to
over-exertion, excitement, over-indulgence in tobacco or alcohol, &c.,
as the balance is more readily upset and any undue strain on the heart
may cause a breakdown of compensation. When this occurs treatment is
required. A period of rest in bed is often sufficient to enable the
heart to recover, and this may be supplemented as required by the
administration of mercurial and saline purgatives to relieve the
embarrassed circulation, and of suitable cardiac tonics, such as
digitalis and strychnin, to reinforce and strengthen the heart's action.
2. _Affections of the Muscular Wall of the Heart._--Dilatation of the
heart, or stretching of the walls of the heart, is an incident, as has
already been stated, in pericarditis and in the earlier stages of
valvular disease antecedent to hypertrophy. Temporary over-distension or
dilatation of the cavities of the heart occurs in violent and protracted
exertion, but rapidly subsides and is in no wise harmful to the sound
and vigorous heart of the young. It is otherwise if the heart is weak
and flabby from a too sedentary life or degenerative changes in its
walls or during convalescence from a severe illness, when the same
circumstances which will not injure a healthy heart, may give rise to
serious dilatation from which recovery may be very protracted.
Influenza is a common cause of cardiac dilatation, and is liable to be a
source of trouble after the acute illness has subsided, if the patient
goes about and resumes his ordinary avocations too soon.
Fatty or fibroid degeneration of the heart wall may occur in later life
from impaired nutrition of the muscle, due to partial obstruction of the
blood-vessels supplying it, when they are the seat of the degenerative
changes known as arteriosclerosis or atheroma. The affection known as
_angina pectoris_ (q.v.) may be a further consequence of this defective
blood-supply.
The treatment will vary according to the nature of the case. In serious
cases of dilatation, rest in bed, purgatives and cardiac tonics may be
required.
In commencing degenerative change the Oertel treatment, consisting of
graduated exercise up a gentle slope, limitation of fluids and a special
diet, may be indicated.
In cases of slight dilatation after influenza or recent illness, the
Schott treatment by baths and exercises as carried out at Nauheim may be
sometimes beneficial. The change of air and scene, the enforced rest,
the placid life, together with freedom from excitement and worry, are
among the most important factors which contribute to success in this
class of case.
_Disorders of Rhythm of the Heart's Action._--Under this heading may be
grouped a number of conditions to which the name "functional affections
of the heart" has sometimes been applied, inasmuch as the disturbances
in question cannot usually be attributed to definite organic disease of
the heart. We must, of course, exclude from this category the
irregularity in the force and frequency of the pulse, which is commonly
associated with incompetence of the mitral valve.
The heart is a muscular organ possessing certain properties,
rhythmicity, excitability, contractility, conductivity and tonicity, as
pointed out by Gaskell, in virtue of which it is able to maintain a
regular automatic beat independently of nerve stimulation. It is,
however, intimately connected with the brain, blood-vessels and the
abdominal and thoracic viscera, by innumerable nerves, through which
impulses or messages are being constantly sent to and received from
these various portions of the body. Such messages may give rise to
disturbances of rhythm with which we are all familiar. For instance,
sudden fright or emotion may cause a momentary arrest of the heart's
action, and excitement or apprehension may set up a rapid action of the
heart or _palpitation_. Palpitation, again, is often the result of
digestive disorders, the message in this case being received from the
stomach, instead of the brain as in emotional disturbances. It may also
result from over-indulgence in tobacco and alcohol.
_Tachycardia_ is the name applied to a more or less permanent increase
in the rate of the heart-beat. It is usually a prominent feature in the
affection known as Graves' disease or exophthalmic goitre. It may also
result from chronic alcoholism. In the condition known as paroxysmal
tachycardia there appears to be no adequate explanation for its onset.
_Bradycardia_ or abnormal slowness of the heart-beat, is the converse of
tachycardia. An abnormally slow pulse is met with in melancholia,
cerebral tumour, jaundice and certain toxic conditions, or may follow an
attack of influenza. There is, however, a peculiar affection
characterized by abnormal slowness of pulse (often ranging as low as
30), and the onset, from time to time, of epileptiform or syncopal
attacks. To this the name "Stokes-Adams disease" has been applied, as it
was first called attention to by Adams in 1827, and subsequently fully
described by Stokes in 1836. It is usually associated with senile
degenerative change of the heart and vascular system, and is held to be
due to impairment of conductivity in the muscular fibres (bundle of His)
which transmit the wave of contraction from the auricle to the
ventricle. It is of serious significance in view of the symptoms
associated with it.
_Intermittency of the Pulse._--By this is understood a pulse in which a
beat is dropped from time to time. The dropping of a beat may occur at
regular intervals every two, four or six beats, &c., or occasionally at
irregular intervals after a series of normal beats. On examining the
heart, it is found, as a rule, that the cause of the intermission at the
wrist is not actual omission of a heart-beat, but the occurrence of a
hurried imperfect cardiac contraction which does not transmit a
pulse-wave to the wrist. It is not characteristic of any special form of
heart affection, and is rarely of serious import. It may be due to
reflex digestive disturbances, or be associated with conditions of
nervous breakdown and irritability, or with an atonic and relaxed
condition of the heart muscle. The treatment of these disorders of
rhythm of the heart will vary greatly according to the cause and is
often a matter of considerable difficulty. (J. F. H. B.)
_Surgery of Heart and Pericardium._--As the result of acute or chronic
inflammation of the lining membrane of the fibrous sac which surrounds
the heart and the neighbouring parts of the large blood-vessels, a
dropsical or a purulent collection may form in it, or the sac may be
quietly distended by a thin watery fluid. In either case, but especially
in the latter, the heart may be so embarrassed in its work that death
seems imminent. The condition is generally due to the cultivation in the
pericardium of the germs of rheumatism, influenza or gonorrhoea, or of
those of ordinary suppuration. Respiration as well as circulation is
embarrassed, and there is a marked fulness and dulness of the front wall
of the chest to the left of the breast-bone. In that region also pain
and tenderness are complained of. By using the slender, hollow needle of
an aspirator great relief may be afforded, but the tapping may have to
be repeated from time to time. If the fluid drawn off is found to be
purulent, it may be necessary to make a trap-door opening into the chest
by cutting across the 4th and 5th ribs, incising and evacuating the
pericardium and providing for drainage. In short, an abscess in the
pericardium must be treated like an abscess in the pleura.
Wounds of the heart are apt to be quickly fatal. If the probability is
that the enfeebled action of the heart is due to pressure from blood
which is leaking into, and is locked up in the pericardium, the proper
treatment will be to open the pericardium, as described above, and, if
possible, to close the opening in the auricle, ventricle or large
vessel, by sutures. (E. O.*)