DISEASES OF THE HEART, BLOOD VESSELS, AND LYMPHATICS.
By W. H. HARBAUGH, V. S.
[Revised by Leonard Pearson, B. S., V. M. D.]
THE CIRCULATORY SYSTEM.
In cattle, as in human beings, the heart, blood vessels, and lymphatics may be described as the circulatory apparatus.
The heart is in the thoracic cavity (chest). It is conical in form, with the base or large part uppermost, while the apex, or point, rests just above the sternum (breastbone). It is situated between the right and left lungs, the apex inclining to the left, and owing to this the heart beats are best felt on the left side of the chest, behind the elbow. The heart may be considered as a hollow muscle, containing four compartments, two on each side. The upper compartments are called auricles and the lower ones ventricles. The right auricle and ventricle are completely separated from the left auricle and ventricle by a thick septum or wall, so that there is no communication between the right and left sides of the organ.
At the bottom of each auricle is the auriculo-ventricular opening, each provided with a valve to close it when the heart contracts to force the blood into the arteries. In the interval between the contractions these valves hang down into the ventricles.
The muscular tissue of the heart belongs to that cla.s.s known as involuntary, because its action is not controlled by the will.
The cavities of the heart are lined by a serous membrane, called the endocardium, which may be considered as a continuation of the veins and the arteries, forming their internal lining. The walls of the ventricles are thicker than those of the auricles, and the walls of the left ventricle are much thicker than those of the right.
The heart is enveloped by a fibrous sac (or bag), called the pericardium, which a.s.sumes much of the general shape of the outer surface of the heart.
The action of the heart is similar to that of a pump and its function is to keep the blood in circulation. The auricles may be considered as the reservoirs or receivers of the blood and the ventricles as the pump chambers. During the interval between contractions, the heart being in momentary repose, the blood pours into the auricles from the veins; the auriculo-ventricular orifices being widely open, the ventricles also receive blood; the auricles contract and the ventricles are filled; contraction of the ventricles follows; the auriculo-ventricular valves are forced up by the pressure of the blood and close the auriculo-ventricular openings and prevent the return of blood into the auricles; the contraction of the ventricles forces the blood from the right ventricle into the lungs through the pulmonary artery and its branches, and from the left ventricle into the aorta, thence through the arteries to all parts of the body. After the contraction of the ventricles the heart is again in momentary repose and is being filled with blood, while the valves in the aorta and pulmonary artery close to prevent the return of blood into the ventricles. (See Pl.
VII.)
The average weight of the heart of an ox is said to be from 3-1/2 to 5 pounds; but, of course, owing to the many breeds and sizes of cattle, it must vary in different animals.
The vessels that convey the blood from the heart to all parts of the body are called arteries; those which return the blood to the heart are called veins. The arteries divide and subdivide (like the branches of a tree), become smaller and smaller, and ultimately ramify into every part of the body. Between the ultimate ramifications of the arteries and the beginning of the veins there is an intermediate system of very minute vessels called capillaries, which connect the arterial with the venous system of the circulation. The walls of the arteries are possessed of a certain amount of rigidity, sufficient to keep the tubes open when they are empty.
The blood leaves the left ventricle through a single vessel, the common aorta, consisting of the anterior and posterior aortas, which give off the large arteries.
The veins take the blood from the capillaries in all parts of the body.
They begin in very small tubes, which unite to become larger in size and less in number as they approach the heart.
In its course an artery is usually accompanied with a vein and in many situations with a nerve. The more important arteries are placed deep within the body; when they are superficial, however, they are generally found where least exposed to injury, as, for example, on the inner side of the legs. Arteries are less numerous than veins, and their total capacity is much less than that of the veins. A great number of veins are in the tissue immediately beneath the skin and do not generally accompany arteries.
The blood, throughout its course in the heart, arteries, capillaries, and veins, is inclosed within these vessels. Except where the large lymphatics empty into the venous blood, there is no opening into the course of the blood.
All the arteries except the pulmonary and its branches carry bright-red blood, and all the veins, except the pulmonary veins, carry dark-red blood.
The impure dark-red blood is collected from the capillary vessels and carried to the right auricle by the veins; it pa.s.ses down into the right ventricle, and thence into the pulmonary artery and through its branches to the capillaries of the lungs, where the carbonic-acid gas and other impurities are given up to the air in the air cells of the lungs (through the thin walls between the capillaries and the air cells), and where it also absorbs from the air the oxygen gas necessary to sustain life. This gas changes it to the bright-red, pure blood. It pa.s.ses from the capillaries to the branches of the pulmonary veins, which convey it to the left auricle of the heart; it then pa.s.ses through the auriculo-ventricular opening into the left ventricle, the contraction of which forces it through the common aorta into the posterior and anterior aortas, and through all the arteries of the body into the capillaries, where it parts with its oxygen and nutritive elements and where it absorbs carbonic-acid gas and becomes dark colored. (See theoretical diagram of the circulation, Pl.
VII.)
The branches of certain arteries in different parts unite again after subdividing. This reuniting is called anastomosing, and a.s.sures a quota of blood to a part if one of the anastomosing arteries should be tied in case of hemorrhage, or should be destroyed by accident or operation.
THE BLOOD.
The various kinds of food, after being digested in the alimentary ca.n.a.l, are absorbed and carried into the blood by the lymphatics, and by the blood to the places where nutrition is required. The blood takes from all parts of the body all that is no longer required, and carries it to the different organs through which it is eliminated from the body. It contains within itself all the elements which nourish the body.
The blood may be considered as a fluid holding in solution certain inorganic elements and having certain bodies suspended in it. To facilitate description, the blood may be considered as made up of the corpuscles and the liquor sanguinis. The corpuscles are of two kinds, the red and the white, the red being the more numerous. The color of the blood is caused by the coloring matter in the red corpuscles, which are the oxygen carriers.
Both kinds are very minute bodies, which require the aid of the microscope to recognize them. The liquor sanguinis is composed of water containing in solution salts, alb.u.men, and the elements of fibrin.
The lymphatics, or absorbents, are the vessels which carry the lymph and chyle in the blood. They begin as capillaries in all parts of the body, gradually uniting to form larger trunks. Placed along the course of the lymphatic vessels are glands, in some situations collected into groups; for example, in the groin. These glands are often involved in inflammation arising from the absorption of deleterious matter.
Absorption is the function of the lymphatics. The liquor sanguinis pa.s.ses from the blood capillaries to supply nutrition to the tissues. All of the liquor sanguinis that is not required is absorbed by the lymphatic vessels and conveyed back to the blood by the lymphatic ducts. The lymphatics which proceed from the intestines convey the chyle into the blood during digestion. As a rule, the lymphatic vessels follow the course of the veins.
All the absorbent vessels convey their contents to the thoracic duct and right great lymphatic vein, which empty into the anterior vena cava, where the lymph and chyle mix with the venous blood, and thus maintain the supply of nutritive elements in the blood.
THE PULSE.
As fully explained, the heart pumps the blood throughout the arterial system. The arteries are always full and each contraction of the ventricle pumps more blood into them; this distends their elastic walls and sends along them a wave which gradually becomes less perceptible as it nears the very small arteries. This wave const.i.tutes the pulse, and is lost before the capillaries are reached. The sensation or impression given to the finger when placed upon the artery shows the force exerted by the heart and some important facts concerning the condition of the circulation. In adult cattle the average number of pulsations in a minute is from 50 to 60. The pulse is faster than normal after exercise, excitement, on hot days, from pain, and as a result of fullness of the stomach. In old animals it is slower than in the young and in males slightly slower than in females. In fevers and inflammations and in local diseases of the heart the pulse rate is increased. If the rate is greater than 100 or 110 to the minute the outlook for recovery is not good.
Other variations of the pulse are known as infrequent pulse, which means that the number of pulsations in a given time is less than normal. The irregular or the intermittent pulse is when the pulsations do not follow in regular order. The large pulse and the small pulse refer to the volume of the pulse, which may be larger or smaller than usual. The strong pulse and the feeble pulse refer to the strength or weakness of the pulsation. The pulse is said to be hard when the vessel feels hard and incompressible, the soft pulse being the opposite. By dicrotic pulse is meant that kind of pulsation which makes each beat seem double, and therefore it is generally called the double pulse.
The venous or "jugular pulse" is the pulsation so frequently observed in the jugular vein of cattle and is particularly noticeable while they are ruminating--"chewing the cud." It is not always a.s.sociated with disease, but may be a symptom of some disease of the heart; in such cases the jugular pulse is continuous.
The place selected for feeling the pulse in cattle is where the submaxillary artery winds around the lower jawbones, just at the lower edge of the flat muscle on the side of the cheek; or, if the cow is lying down, the metacarpal artery on the back part of the fore fetlock is very convenient for the purpose.
THE EXAMINATION OF THE HEART.
Corresponding to the beats of the heart two sounds are emitted which are of a definite type in healthy animals. The first is produced by the contraction of the heart and the flow of blood out of it; the second is caused by the rebound of blood in the aorta and the closure of the valves that prevent it from flowing backward into the heart, whence it came. The first sound is the longer and louder of the two, though of low pitch. The second sound is sharper and shorter, and is not always easy to hear. There is a brief interval between them.
To distinguish these sounds, the ear is placed against the left side of the chest, a little above the point where the elbow rests when the animal is standing in a natural position, and about opposite the sixth rib. Both heart sounds are reduced in intensity when the animal is weak or when the heart is forced away from the chest wall by collections of fluid or by tubercular or other growths. Nonrhythmical heart sound is often caused by pericarditis or by disease of the valves. It may also be attributable to overfilling of the heart upon the right side, as occurs in severe congestion of the lungs and in some febrile diseases.
In pericarditis, sounds like sc.r.a.ping, rubbing, or splashing may be heard, entirely apart from the two normal sounds above described.
The impulse of the heart, as felt by placing the hand against the chest, is of some consequence in reaching a conclusion in respect to disease of the heart; but it must be remembered that the impulse may be very much increased by diseases other than those of the heart, as, for example, inflammation of various organs, severe pains, etc. The impulse may be increased also (when disease does not exist) by work, exercise, fright, or any cause of excitement, or, in general, by anything that causes acceleration of the pulse.
The impulse of the heart may be felt and the sounds may be heard fairly well in lean cattle, but in fat ones it is difficult and often impossible to detect either impulse or sound with any degree of satisfaction.
PALPITATION.
When the impulse of the heart is excessive--that is, when it beats more or less tumultuously--the familiar expression "palpitation of the heart" is applied; by many it is called "thumps." The hand or ear placed against the chest easily detects the unnatural beating. In some cases it is so violent that the motion may be seen at a distance. Palpitation is but a symptom, and in many instances not connected with disease of the structure of the heart or its membranes. A badly frightened animal may have palpitation.
When it comes on suddenly and soon pa.s.ses away, it depends on some cause other than diseases of the heart; when it is gradually manifested, however, and becomes constant, although more p.r.o.nounced at one time than another, heart disease may be suspected, especially if other symptoms of heart disease are present.
INJURY TO THE HEART BY FOREIGN BODIES.
Cattle are addicted to the habit of chewing and swallowing many objects not intended as articles of food. Every veterinarian of experience has met with instances to remind him of this, and it is well known to butchers. Among the great variety of things that have thus found their way into the stomachs of cattle the following have been noticed: Finger rings, knitting needles, old shoes, table knives, wood, pieces of leather, pieces of wire, b.u.t.tons, hairpins, brushes, nails, coins, etc. The more sharply pointed objects sometimes penetrate the wall of the stomach, in some cases causing gastric irritation enough to produce indigestion, gradually work their way through the diaphragm toward the heart, pierce the pericardium (bag inclosing the heart), wound the heart, and thus prove fatal to the animal.
Cases are recorded in which the foreign body has actually worked its way into one of the cavities of the heart. Instances are known, however, in which the object took a different course, and finally worked its way toward the surface and was extracted from the wall of the chest. While it is possible that the foreign body may pierce the wall at different parts of the alimentary ca.n.a.l, as it frequently does that of the rumen (paunch), it is thought that in most cases it pa.s.ses through the wall of the reticulum (smaller honeycombed compartment, or second stomach) and is drawn toward the heart by the suctionlike action of the chest. Post-mortem examinations have demonstrated the course it pursued, as adhesions and other results of the inflammation it caused were plainly to be seen. All manner of symptoms may precede those showing involvement of the heart, depending upon the location of the foreign body and the extent of inflammation caused by it.
Severe indigestion may occur; stiffness and difficulty in moving about owing to the prods of the sharp body following muscular contraction; pain on pressure over the front, lower, or right side of the abdomen; coughing and difficult, quick breathing. In most cases the foreign body does not penetrate to the heart, nor even to the pericardium.
_Symptoms._--The symptoms are as follows: The animal is disinclined to move actively, the step is restricted and cautious, sudden motion causes grunting, the att.i.tude is constrained, the feet are drawn somewhat together, the back is arched, the face has an anxious expression. If the disease is of several days" standing, there is likely to be soft swelling (edema) beneath the neck, in the dewlap, and under the chest, between the fore legs. Breathing is short and difficult; it may clearly be painful. The pulse is rapid, 80 to 120 per minute. The muscles quiver as though the animal were cold. Rumination and appet.i.te are depressed or checked. The dung is hard, and to void it appears to cause pain. These symptoms usually develop gradually, and, of course, they vary considerably in different animals, depending upon the size and location of the foreign body and the irritation it causes.
As a matter of course, in such cases treatment is useless, but when it is possible to diagnose correctly the animal could be turned over to the butcher before the flesh becomes unfit for use; that is, before there is more than a little suppuration and before there is fever. Knowing that cattle are p.r.o.ne to swallow such objects, ordinary care may be taken in keeping their surroundings as free of them as possible.
PERICARDITIS.