the animal usually dies within four days. The first symptoms which
attract the attention of the owner is difficulty in chewing and
swallowing, an extension of the head and protrusion over the inner part
of the eye of the membrana nictitans, or haw. An examination of the
mouth will reveal an inability to open the jaws to their full extent,
and the endeavor to do so will produce great nervous excitability and
increased spasm of the muscles of the jaw and neck. The muscles of the
neck and along the spine become rigid and the legs are moved in a stiff
manner. The slightest noise or disturbance throws the animal into
increased spasm of all the affected muscles. The tail is usually
elevated and held immovable; the bowels become constipated early in the
attack. The temperature and pulse are not much changed. These symptoms
in the acute type become rapidly aggravated until all the muscles are
rigid--in a state of tonic spasm--with a continuous tremor running
through them; a cold perspiration breaks out on the body; the breathing
becomes painful from the spasm of the muscles used in respiration; the
jaws are completely set, eyeballs retracted, lips drawn tightly over the
teeth, nostrils dilated, and the animal presents a picture of the most
extreme agony until death relieves him. The pulse, which at first was
not much affected, will become quick and hard, or small and thready when
the spasm affects the muscles of the heart. In the subacute cases the
jaws may never become entirely locked; the nervous excitability and
rigidity of the muscles are not so great. There is, however, always some
stiffness of the neck or spine manifest in turning; the haw is turned
over the eyeball when the nose is elevated. It is not uncommon for
owners to continue such animals at their work for several days after the
first symptoms have been observed. All the symptoms may gradually
increase in severity for a period of ten days, and then gradually
diminish under judicious treatment, or they may reach the stage wherein
all the characteristics of acute tetanus become developed. In some
cases, however, we find the muscular cramps almost solely confined to
the head or face, perhaps involving those of the neck. In such cases we
have complete trismus (lockjaw), and all the head symptoms are acutely
developed. On the contrary, we may find the head almost exempt in some
cases, and have the body and limbs perfectly rigid and incapable of
movement without falling.
Tetanus may possibly be confounded with spinal meningitis, but the
character of the spasm-locked jaw, retraction of the eyeballs, the
difficulty in swallowing due to spasms of the muscles of the pharynx,
and above all, the absence of paralysis, should serve to make the
distinction.
_Prevention._--When a valuable horse has sustained a wound that it is
feared may be followed by tetanus, it is well to administer a dose of
tetanus antitoxin. This is injected beneath the skin with a hypodermic
syringe. A very high degree of protection may in this way be afforded.
This antitoxin should be administered only by a competent veterinarian.
_Treatment._--The animal should be placed in a box stall without
bedding, as far as possible from other horses. If in a country district,
the animal should be put into an outbuilding or shed, where the noise of
other animals will not reach it; if the place is moderately dark, it is
all the better; in fly time it should be covered with a light sheet. The
attendant must be very careful and quiet to prevent all unnecessary
excitement and increase of spasm. Tetanus antitoxin appears to be useful
as a remedy in some cases, if given in very large quantities early in
the disease; otherwise it is useless. Subcutaneous injections of
carbolic acid in glycerin and water (carbolic acid 30 grains, glycerin
and water each 1 ounce) appear to be useful in some cases. Injections
should be given twice daily.
A cathartic, composed of Barbados aloes 6 to 8 drams, with which may be
mixed 2 drams of the solid extract of belladonna, should be given at
once. This is best given in a ball form; if, however, the animal is
greatly excited by the attempt or can not swallow, the ball may be
dissolved in 2 ounces of olive oil and thrown on the back of the tongue
with a syringe. If the jaws are set, or nearly so, an attempt to
administer medicine by the mouth should not be made. In such cases
one-quarter of a grain of atropia, with 5 grains of sulphate of morphia,
should be dissolved in 1 dram of pure water and injected under the skin.
This should be repeated sufficiently often to keep the animal
continually under its effect. This will usually mitigate the severity of
the spasmodic contraction of the affected muscles and lessen sensibility
to pain. Good results may be obtained sometimes by the rectal injection
of the fluid extract of belladonna and of cannabis indica, of each 1
dram, every four or six hours. This may be diluted with a quart of milk.
When the animal is unable to swallow liquids, oatmeal gruel and milk
should be given by injection per rectum to sustain the strength of the
animal. A pailful of cool water should be constantly before him, placed
high enough for him to reach it without special effort; even if drinking
is impossible, the laving of the mouth is refreshing. Excellent success
frequently may be obtained by clothing the upper part of the head, the
neck, and greater part of the body in woolen blankets kept saturated
with very warm water. This treatment should be continued for six or
eight hours at a time. It often relaxes the cramped muscles and gives
them rest and the animal almost entire freedom from pain; but it should
be used every day until the acute spasms have permanently subsided in
order to be of any lasting benefit.
Recently subcutaneous injections of brain emulsion have been
recommended. It is thought that the tetanus toxin will attach itself to
the brain cells so injected and thus free the system of this poison.
When it is due to a wound, the wound should be thoroughly cleaned and
disinfected with carbolic acid. If from a wound which has healed, an
excision of the cicatrix may be beneficial. In all cases it is not
uncommon to have a partial recovery followed by relapse when the animal
becomes excited from any cause.
RABIES, HYDROPHOBIA, OR MADNESS.
This disease does not arise spontaneously among horses, but is the
result of a bite from a rabid animal--generally a dog or cat. The
development of the disease follows the bite in from three weeks to three
months--very rarely in two weeks. (See also p. 559.)
_Symptoms._--The first manifestation of the development of this disease
may be an increased excitability and viciousness; very slight noises or
the approach of a person incites the animal to kick, strike, or bite at
any near object. Very often the horse will bite his own limbs or sides,
lacerating the flesh and tearing the skin. The eyes appear staring,
bloodshot; the ears are on the alert to catch all sounds; the head is
held erect. In some cases the animal will continually rub and bite the
locality of the wound inflicted by the rabid animal. This symptom may
precede all others. Generally the bowels become constipated and the
animal makes frequent attempts at urination, which is painful, and the
urine very dark colored. The furious symptoms appear in paroxysms; at
other times the animal may eat and drink, although swallowing appears to
become painful toward the latter stage of the disease, and may cause
renewed paroxysms. The muscles of the limbs or back may be subject to
intermittent spasms, or spasmodic tremors; finally, the hind limbs
become paralyzed, breathing very difficult, and convulsions supervene,
followed by death. The pulse and respirations are increased in frequency
from the outset of the attack. Rabies may possibly be mistaken for
tetanus. In the latter disease we find tonic spasms of the muscles of
the jaws, or stiffness of the neck or back very early in the attack, and
evidence of viciousness is absent.
_Treatment._--As soon as the true nature of the disease is ascertained
the animal should be killed.
_Prevention._--When a horse is known to have been bitten by a rabid
animal, immediate cauterization of the wound with a red-hot iron may
possibly destroy the virus before absorption of it takes place.
PLUMBISM, OR LEAD POISONING.
This disease is not of frequent occurrence. It may be due to the
habitual drinking of water which has been standing in leaden conductors
or in old paint barrels, etc. It has been met with in enzootic form near
smelting works, where, by the fumes arising from the works, lead in the
form of oxid, carbonate, or sulphate was deposited on the grass and
herbage which the horses ate.
_Symptoms._--Lead poisoning produces derangement of the functions of
digestion and locomotion, or it may affect the lungs principally. In
whatever system of organs the lead is mostly deposited there we have the
symptoms of nervous debility most manifest. If in the lungs, the
breathing becomes difficult and the animal gets out of breath very
quickly when compelled to run. Roaring, also, is very frequently a
symptom of lead poisoning. When it affects the stomach, the animal
gradually falls away in flesh, the hair becomes rough, the skin tight,
and colicky symptoms develop. When the deposit is principally in the
muscles, partial or complete paralysis gradually develops. When large
quantities of lead have been taken in and absorbed, symptoms resembling
epilepsy may result, or coma and delirium develop and prove fatal. In
lead poisoning there is seldom any increase in temperature. A blue line
forms along the gums of the front teeth, and the breath assumes a
peculiarly offensive odor. Lead can always be detected in the urine by
chemical tests.
_Treatment._--The administration of 2-dram doses of iodid of potassium
three times a day is indicated. This will form iodid of lead in the
system, which is rapidly excreted by the kidneys. If much muscular
weakness or paralysis is present, sulphate of iron in 1-dram doses and
strychnia in 2-grain doses may be given twice a day. In all cases of
suspected lead poisoning all utensils which have entered into the supply
of feed or water should be examined for the presence of soluble lead. If
it occurs near lead works, great care must be given to the supply of
uncontaminated fodder, etc.
UREMIA.
Uremic poisoning may affect the brain in nephritis, acute albuminuria,
or when, from any cause, the functions of the kidneys become impaired or
suppressed and urea (a natural product) is no longer eliminated from
these organs, causing it to accumulate in the system and give rise to
uremic poisoning.
Uremic poisoning is usually preceded by dropsy of the limbs or abdomen;
a peculiar, fetid breath is often noticed; then drowsiness, attacks of
diarrhea, and general debility ensue. Suddenly extreme stupor or coma
develops; the surface of the body becomes cold; the pupils are
insensible to light; the pulse slow and intermitting; the breathing
labored, and death supervenes. The temperature throughout the disease is
seldom increased, unless the disease becomes complicated with acute,
inflammatory disease of the brain or respiratory organs, which often
occur as a result of the urea in the circulation. Albumen and tube casts
may frequently be found in the urine. The disease almost invariably
proves fatal.
Treatment must be directed to a removal of the cause.
ELECTRIC SHOCK.
Electric shock, from coming in contact with electric wires, is becoming
a matter of rather frequent occurrence, and has a similar effect upon
the animal system as a shock from lightning. Two degrees of electric or
lightning shock may be observed, one producing temporary contraction of
muscles and insensibility, from which recovery is possible, the other
killing directly, by producing a condition of nervous and general
insensibility. In shocks which are not immediately fatal the animal is
usually insensible, the respiration slow, labored, or gasping, the pulse
slow, feeble, and irregular, and the pupils dilated and not sensitive,
or they may be contracted and sensitive. The temperature is lowered.
There may be a tendency to convulsions or spasms. The predominating
symptoms are extreme cardiac and respiratory depression.
_Treatment._--Sulphate of atropia should be given hypodermically in
one-quarter grain doses every hour or two hours until the heart beats
are invigorated, the number and fullness of the respirations increased,
and consciousness returns. Stimulating injections per rectum may also be
useful in arousing the circulation; for this purpose whisky or ammonia
water may be used.
DISEASES OF THE HEART, BLOOD VESSELS, AND LYMPHATICS.
By M. R. TRUMBOWER, V. S.
[Revised by Leonard Pearson, B. S., V. M. D.]
ANATOMY AND PHYSIOLOGY OF THE HEART AND BLOOD VESSELS.
(Pls. XX and XXI.)
The heart is a hollow, muscular organ, situated a little to the left of
the center of the chest. Its impulse is felt on the left side on account
of its location and from the rotary movement of the organ in action. It
is cone-shaped, with the base upward; the apex points downward,
backward, and to the left side. It extends from about the third to the
sixth ribs, inclusive. The average weight is about 7 to 8 pounds. In
horses used for speed the heart is relatively larger, according to the
weight of the animal, than in horses used for slow work. It is suspended
from the spine by the large blood vessels and held in position below by
the attachment of the pericardium to the sternum. It is inclosed in a
sac, the pericardium, which is composed of a dense fibrous membrane
lined by a delicate serous membrane, which is reflected over the heart;
the inner layer is firmly adherent to the heart, the outer to the
fibrous sac, and there is an intervening space, known as the pericardial
space, in which a small amount of serum--a thin translucent liquid--is
present constantly.
The heart is divided by a shallow fissure into a right and left side;
each of these is again subdivided by a transverse partition into two
compartments which communicate. Thus there are four cardiac
cavities--the superior, or upper, ones called the auricles; the
inferior, or lower, ones the ventricles. These divisions are marked on
the outside by grooves, which contain the cardiac blood vessels, and are
generally filled with fat.
The right side of the heart may be called the venous side, the left the
arterial side, named from the kind of blood which passes through them.
The auricles are thin-walled cavities placed at the base, and are
connected with the great veins--the venae cavae and pulmonary
veins--through which they receive blood from all parts of the body. The
auricles communicate with the ventricles each by a large aperture, the
auriculo-ventricular orifice, which is furnished with a remarkable
mechanism of valves, allowing the transmission of blood from the
auricles into the ventricles, but preventing a reverse course. The
ventricles are thick-walled cavities, forming the more massive portion
of the heart toward the apex. They are separated by a partition, and are
connected with the great arteries--the pulmonary artery and the
aorta--by which they send blood to all parts of the body. At the mouth
of the aorta and at the mouth of the pulmonary artery is an arrangement
of valves in each case which prevents the reflux of blood into the
ventricles. The auriculo-ventricular valve in the left side is composed
of two flaps, hence it is called the bicuspid valve; in the right side
this valve has three flaps and is called the tricuspid valve. The flaps
which form these valves are connected with a tendinous ring between the
auricles and ventricles; and each flap of the auriculo-ventricular
valves is supplied with tendinous cords, which are attached to the free
margin and under-surface, so as to keep the valves tense when closed--a
condition which is produced by the shortening of muscular pillars with
which the cords are connected. The arterial openings, both on the right
and on the left side, are provided with three-flapped semilunar-shaped
valves, to prevent the regurgitation of blood when the ventricles
contract. The veins emptying into the auricles are not capable of
closure, but the posterior vena cava has an imperfect valve at its
aperture.
The inner surface of the heart is lined by a serous membrane, the
endocardium, which is smooth and firmly adherent to the muscular
structure of the heart. This membrane is continuous with the lining
membrane of the blood vessels, and it enters into the formation of the
valves.
The circulation through the heart is as follows: The venous blood is
carried into the right auricle by the anterior and posterior venae cavae.
It then passes through the right auriculo-ventricular opening into the
right ventricle, thence through the pulmonary artery to the lungs. It
returns by the pulmonary veins to the left auricle, then is forced
through the auriculo-ventricular opening into the left ventricle, which
propels it through the aorta and its branches into the system, the veins
returning it again to the heart. The circulation, therefore, is double,
the pulmonary, or lesser, being performed by the right side, and the
systemic, or greater, by the left side.
As the blood is forced through the heart by forcible contractions of its
muscular walls, it has the action of a force pump, and gives the impulse
at each beat, which we call the pulse--the dilatation of the arteries
throughout the system. The contraction of the auricles is quickly
followed by that of the ventricles, and then a slight pause occurs; this
takes place in regular rhythmical order during health.
[Illustration: PLATE XX.
INTERIOR OF CHEST SHOWING POSITION OF HEART AND DIAPHRAGM.]
[Illustration: PLATE XXI.
Heart.
Right half, red.
Left half, blue.
Auricles, at upper end.
Ventricles, at lower end.
Arteries, red.
Veins, blue.
1. Left carotid artery.
2. Left jugular vein.
3. Portal system.
4. Vessels of the liver.
5. Arteries of the stomach. (Caeliac axis).
6. Vessels of the large intestine.
7. Vessels of the small intestine.
8. Artery of left kidney.
CIRCULATORY APPARATUS.]
The action of the heart is governed and maintained by the pneumogastric
nerve (tenth pair of cranial nerves); it is the inhibitory nerve of the
heart, and regulates, slows, and governs its action. When the nerve is
cut, the heartbeats increase rapidly, and, in fact, the organ works
without control. When the nerve is unduly irritated the holdback, or
inhibitory force, is increased, and the heart slows up in the same
measure. The left cavities of the heart, the pulmonary veins, and the
aorta, or systemic artery, contain red or florid blood, fit to circulate
through the body. The right cavities of the heart, with the venae cavae,
or systemic veins, the pulmonary artery, contain dark blood, which must
be transmitted through the lungs for renovation.
The arteries, commencing in two great trunks, the aorta and the
pulmonary artery, undergo division, as in the branching of a tree. Their
branches mostly come off at acute angles, and are commonly of uniform
diameter in each case, but successively diminish after and in
consequence of division, and in this manner gradually merge into the
capillary system of blood vessels. As a general rule, the combined area
of the branches is greater than that of the vessels from which they
emanate, and hence the collective capacity of the arterial system is
greatest at the capillary vessels. The same rule applies to the veins.
The effect of the division of the arteries is to make the blood move
more slowly along their branches to the capillary vessels, and the
effect of the union of the branches of the veins is to accelerate the
speed of the blood as it returns from the capillary vessels to the
venous trunks.
In the smaller vessels a frequent running together, or anastomosis,
occurs. This admits of a free communication between the currents of
blood, and must tend to promote equability of distribution and of
pressure, and to obviate the effects of local interruption. The arteries
are highly elastic, being extensile and retractile both in length and
breadth. During life they are also contractile, being provided with
muscular tissue. When cut across they present, although empty, an open
orifice; the veins, on the other hand, collapse.
In most parts of the body the arteries are inclosed in a sheath formed
of connective tissue, but are connected so loosely that, when the vessel
is cut across, its ends readily retract some distance within the sheath.
Independently of this sheath, arteries are usually described as being
formed of three coats, named, from the relative positions, external,
middle, and internal. This applies to their structure so far as it is
discernible by the naked eye. The internal, serous, or tunica intima, is
the thinnest, and is continuous with the lining membrane of the heart.
It is made up of two layers--an inner, consisting of a layer of
epithelial scales, and an outer, transparent, whitish, highly elastic,
and perforated. The middle coat, tunica media, is elastic, dense, and
of a yellow color, consisting of nonstriated muscular and elastic
fibers, thickest in the largest arteries and becoming thinner in the
smaller. In the smallest vessels it is almost entirely muscular. The
external coat, tunica adventitia, is composed mainly of fine and closely
woven bundles of white connective tissue, which chiefly run diagonally
or obliquely around the vessel. In this coat the nutrient vessels, the
vasa vasorum, form a capillary network, from which a few penetrate as
far as the muscular coat.
The veins differ from arteries in possessing thinner walls, less elastic
and muscular tissue, and for the most part a stronger tunica adventitia.
They collapse when cut across or when they are empty. The majority of
veins are provided with valves; these are folds of the lining membrane,
strengthened by fibrous tissue. They favor the course of the blood and
prevent its reflux. The nerves which supply both the arteries and the
veins come from the sympathetic system. The smaller arteries terminate
in the system of minute vessels known as the capillaries, which are
interposed between the termination of the arteries and the commencement
of the veins. Their average diameter is about one three-thousandth of an
inch.
DISEASES OF THE HEART AND BLOOD VESSELS.
In considering diseases of the heart we meet with many difficulties,
depending much upon the position which this organ occupies in the
animal. The shoulders cover so much of the anterior portion of the
chest, and often in very heavy-muscled horses the chest walls are so
thick that a satisfactory examination of the heart is attended with
difficulty. Diseases of the heart are not uncommon among horses; the
heart and its membranes are frequently involved in diseases of the
respiratory organs, diseases of the kidneys, rheumatism, influenza, etc.
Some of the diseases of this organ are never suspected by the ordinary
observer during life, and are so difficult to diagnose with any degree
of certainty that we will have to confine ourselves to a general
outline, giving attention to such symptoms as may serve to lead to a
knowledge of their existence, with directions for treatment, care, etc.
Nervous affections often produce prominent heart symptoms by causing
functional disturbance of that organ, which, if removed, will leave the
heart restored to perfect vigor and normal action. Organic changes
involving the heart or valves, however, usually grow worse and
eventually prove fatal. Therefore it is necessary that we arrive at an
appreciation of the true nature and causes so that we may be able to
form a true estimate of the possibilities for recovery or encouragement
for medical treatment.
Disease of the heart may occur at any age, but it is witnessed most
frequently in young horses, which, when being trained for fast work, are
often subjected to excessive hardship and fatigue. Nervous or timid
animals also suffer from such diseases more frequently than those of a
sluggish disposition. Any cause which induces a violent or sudden change
in the circulation may result in injury to the heart. Symptoms which may
frequently denote disease of the heart are difficult breathing or
short-windedness, dropsies of the limbs, habitual coldness of the
extremities, giddiness or fainting attacks, inability to stand work,
although the general appearance would indicate strength and ability,
etc.
MYOCARDITIS, OR INFLAMMATION OF THE MUSCULAR STRUCTURE OF THE HEART.
The heart muscle sometimes becomes inflamed as a complication or result
of the existence of general or febrile and of infectious diseases.
Severe influenza or infectious pneumonia is not infrequently followed by
myocarditis. By extension of inflammation of the endocardium or
pericardium the muscle of the heart may become involved. Overexertion or
especially hard work continued for a long time may cause this muscle to
become inflamed.