GENERAL DISCUSSION.--The circulatory organs are the heart, arteries, veins and lymphatics. The _heart_ is the central organ of the circulatory system (Fig. 23). Its function is to force the blood through the blood-vessels. It is situated in the thoracic cavity between the lungs, and enclosed by a special fold of the pleura, the pericardial sack. There are two kinds of blood-vessels, arteries and veins. The _arteries_ leave the heart and carry the blood to the many different organs of the body. The _veins_ return to the heart and carry the blood from the body tissues. The _capillaries_ are small blood-vessels, microscopic in size, that connect the arteries with the veins. The arteries carry the pure blood. The opposite is true, however, of the lesser or pulmonary system. The pulmonary artery carries the impure blood to the lungs, and the pulmonary veins carry the pure blood back from the lungs. The _lymphatic vessels_ carry a transparent or slightly colored fluid and chyle from the tissues and alimentary canal.
This system of vessels empties into the venous system.
[Illustration: FIG. 23.--Photograph of model of horse's heart: auricle; ventricle; pulmonary artery; pulmonary veins; posterior aorta; and anterior aorta.]
_The functions of the blood_ are to nourish the body tissues; furnish material for the purpose of the body secretions; supply the cells of the body with oxygen; convey from the tissues injurious substances produced by the cellular activity; and destroy organisms that may have entered the body tissues. The cellular and fluid portions of the blood are not always destructive to disease-producing organisms. In certain infectious diseases, the fluid portion of the blood may contain innumerable organisms, and destruction of the blood cells occurs.
_In inflammation_ of tissue the circulation of the blood in the inflamed part undergoes certain characteristic changes. At the beginning there is an increase in the blood going to the part. This is followed by a slowing of the blood stream in the small vessels, and the collecting of the blood cells in the capillaries and veins. These circulatory changes are followed by the migration of the blood cells, and the escape of the fluid portion of the blood into the surrounding tissue. The character of the above circulatory changes depends on the extent of the injury to the tissue.
PALPITATION.--This disturbance in domestic animals seems to be purely functional. It may occur independent of any organic heart disease. A highly nervous condition, excitement, over-exertion, debility from disease and the feeding of an improper ration are the common causes.
The heart beats are so violent and tumultuous as to shake the body, and be noticed when standing near the animal. The heart sounds are louder than normal and the pulse beats small and irregular. It may be differentiated from spasm of the diaphragm by determining the relationship of the heart beats to the abrupt shocks observed in the costal and flank regions.
_The treatment_ consists in keeping the animal quiet and avoiding any excitement. A quiet stall away from the other animals is best. The treatment of palpitation resulting from some organic heart disease must be directed largely at the original disease. Morphine is commonly used for the treatment of this disorder. Weak, anaemic animals should receive blood and bitter tonics. If we have reason to believe that the disturbance is caused by improper feeding, the animal should receive a spare diet for a few days.
In such cases it is advisable to administer a physic.
PERICARDITIS.--Inflammation of the pericardial sack is usually a secondary disease. It is frequently met with in influenza, contagious pleuropneumonia, hog-cholera and rheumatism. Cattle may suffer from traumatic pericarditis caused by sharp, pointed, foreign bodies passing through the wall of the reticulum and penetrating the pericardial sack. The jagged ends of fractured ribs may cause extensive injury to neighboring parts, and the inflammation spreads to the pericardial sack.
_The symptoms_ of pericarditis may not be recognized at the very beginning when the disease occurs as a complication of influenza, or infectious pleuropneumonia. The manifestation of pain by moving about in the stall, refusing to eat and the anxious expression of the face are the first symptoms that the attendant may notice. The body temperature is higher than normal, and the pulse rapid and irregular. On auscultation, friction sounds that correspond to the tumultuous beats of the heart are heard. When fluid collects within the pericardial sack, the heart beats become feeble and the pulse weak. Labored breathing and bluish discoloration of the lips follow.
The disease usually runs a very acute course. The prognosis is unfavorable.
_The treatment_ recommended in pneumonia is indicated in this disease.
Absolute rest and the feeding of an easily digested, laxative diet is a very essential part of the treatment. At the very beginning morphine may be given to quiet the tumultuous beats of the heart. Cold applications to the chest wall in the form of ice packs should be used. Heart tonics and stimulants such as digitalis, strychnine and alcohol should be administered when the pulse beats weaken. To promote absorption of the exudate, iodide of sodium may be given. Mustard paste, or a cantharides blister applied over the region of the heart is useful in easing the pain and overcoming the inflammation. If fluid collects in sufficient quantity to seriously interfere with the heart action, the sack may be punctured with the trocar and cannula and the fluid withdrawn. Great care must be used to avoid injury to the heart and infection of the part.
[Illustration: FIG. 24.--Elephantiasis in horse.]
ACUTE LYMPHANGITIS.--This is an inflammation of the lymphatic vessels of one or both hind limbs. The attack comes on suddenly and usually occurs in connection with rest, and in horses that are of slow, quiet temperament.
The _exciting cause_ is an infection of the part with bacteria, the infection probably occurring through some abrasion or small wound in the skin.
_The local symptoms_ are swelling, tenderness and lameness in the affected limb. The animal may refuse to support its weight on the affected limb. The lymphatic glands in the region are swollen, and the swelling of the limb pits on pressure. In the chronic form of the disease, the regions of the cannon and foot remain permanently enlarged, and the swelling is more firm than it is in the acute form (Fig. 24).
_The general symptoms_ are high body temperature, rapid pulse and the partial or complete loss of appetite.
_The following treatment_ is recommended: Exercise is indicated in cases that are not sufficiently advanced to cause severe lameness, or inability to use the limb; rest and the application of woollen bandages wrung out of a hot water solution of liquor cresolis compound are recommended; Epsom salts in one-half pound doses may be given and repeated in two or three days; a very light diet of soft feed should be given; liniments should _not_ be applied until the soreness in the limb has subsided; iodide of potassium may be given twice daily with the feed.
QUESTIONS
1. What are the functions of the blood and lymph?
2. State the changes occurring in the circulation in inflamed tissue.
3. What is palpitation? Give the causes and treatment.
4. What are the common causes of pericarditis?
5. Give the causes and treatment of acute lymphangitis.
CHAPTER X
DISEASES OF THE NERVOUS SYSTEM
GENERAL DISCUSSION.--The nervous system may be divided into central and peripheral portions. The _central portion_ comprises the brain or encephalon and the spinal cord. These organs are lodged in the cranial cavity and spinal canal. The nerves and ganglia comprise the _peripheral portion_. The nerves form white cords that are made up of nerve fibres. The ganglia are grayish enlargements formed by nerve cells and supporting tissue, situated at the origin of the nerve trunk or along its course.
_The brain_ is an oval mass of nerve tissue elongated from before to behind, and slightly depressed from above to below. It terminates posteriorly in the spinal cord. It is divided into three portions: _cerebrum, isthmus_ and _cerebellum_ (Fig. 25).
_The cerebrum_ forms the anterior portion. It is divided into two lateral lobes or hemispheres by a deep longitudinal fissure. The surface of the cerebral hemispheres is gray and roughened by pleats or folds separated by grooves or fissures. The gray or cortical layer is distinct from the white or connecting structure. The cortical layer is made up of nerve cells or areas which control the voluntary muscles of the body. It is connected with the special senses of touch, temperature and muscle-sense. The gray layer is connected with the posterior portion of the brain, the isthmus or medulla oblongata, by the white nerve tissue.
_The isthmus_ or _medulla oblongata_ is elongated from before to behind and connects the cerebral hemispheres with the spinal cord, anteriorly and posteriorly. It is divided into several different portions, and is made up largely of white connecting fibres with nuclei of gray matter scattered through them. The isthmus is hollowed out by a system of small ventricles that extend from the cerebral hemispheres to the spinal cord, where they terminate in a small, central canal. The isthmus is the highway between the spinal cord and the higher nerve centres. It has in it certain cell centres that give origin to six of the cranial nerves.
[Illustration: FIG. 25.--Photograph of model of horse's brain: longitudinal section; lateral view; cerebrum; cerebellum; and isthmus.]
The third division of the brain is the _cerebellum_. This is a single mass supported by the isthmus. It is situated posterior to the cerebrum, from which it is separated by a transverse fold of the membranes covering the brain. This mass of nerve tissue is much smaller than the cerebrum. The white nerve tissue forms central nuclei which send out branches that ramify in every direction. The centre of the muscular sense is said to be located in this division of the brain. A second function is the maintenance of body equilibrium through its connection with the nerve of the middle ear.
_The spinal cord_ commences at the posterior opening (occipital foramen) of the cranial cavity, and terminates posteriorly in the lumbar region at the upper third of that portion of the spinal canal belonging to the sacrum. It is thick, white in color, irregularly cylindrical in shape, slightly flattened above and below and reaches its largest diameter in the lower cervical and lumbar regions. The spinal canal is lined by the outer membrane that envelops the cord, which aids in fixing this organ to the wall of the canal. The spinal cord is formed by white and gray nerve tissue. The gray tissue is situated within the white, and it is arranged in the form of two lateral comma-shaped columns connected by a narrow commissure of gray matter. The extremities of the lateral gray columns mark the origin of the superior and inferior roots of the spinal nerves. The white tissue of the cord is also divided into lateral portions by superior and median fissures. The inferior fissure does not extend as far as the gray commissure, leaving the lateral inferior columns connected by a white commissure. There are certain centres in the spinal cord that are capable of carrying on certain reflex actions independent of the chief centre in the brain. The white matter of the cord is made up of paths over which impulses to and from the brain are transmitted.
_There are twelve pairs of cranial nerves_. Two pairs belong exclusively to the special senses, smell and sight. Altogether there are ten pairs that are devoted to functions connected with the head, either as nerves of the special senses or in a motor or sensory capacity (Figs. 26 and 27). There are two pairs distributed to other regions. These are the tenth and eleventh pairs. The tenth pair or pneumogastric is distributed to the vital organs lodged within the body cavities.
There are forty-two or forty-three pairs of spinal nerves given off from the spinal cord. The spinal nerves have two roots, superior and inferior.
The superior is the sensory root and the inferior is the motor root, both uniting to form a mixed nerve trunk. The sensory root possesses a ganglion from which it originates.
Generally speaking, the cerebrospinal system deals with the special senses, movement of skeletal or voluntary muscles and cutaneous and muscular sensations. In addition to the above there is a distinct system termed the sympathetic. The _sympathetic system_ consists of a long cord, studded with ganglia, extending from the base of the neck to the sacrum. The ganglia are connected with the inferior roots of the spinal nerves. This cord is connected with groups of ganglia and nerve fibres in the abdominal region, and this in turn is connected with terminal ganglia in distant tissues.
This system of nerves is distributed to the vital organs of the body.
[Illustration: FIG. 26.--Unilateral facial paralysis caused by injury to seventh cranial nerve; note position of lip.]
[Illustration: FIG. 27.--Bilateral facial paralysis. This colt was affected with facial paralysis when born.]
CONGESTION AND ANAEMIA OF THE BRAIN.--In congestion of the brain, the blood-vessels distributed to the nerve tissue become engorged with blood.
It may be either active or passive.
_The cause of anaemia_ of the brain is an insufficient blood supply. This may be due to an abundant haemorrhage and cardiac weakness caused by shock or organic heart disease.
_The causes of congestion_ of the brain are faulty methods of care and feeding. It sometimes occurs when horses are shipped in poorly ventilated cars, or kept in close stables. Climatic changes, or changing the stable and feed, may cause it. Extremely fat animals and animals that are rapidly putting on fat are predisposed to this disorder. Improper methods of feeding, lack of exercise, constipation and excitement are the most common causes. Passive congestion may result from pressure on the jugular vein by obstructing the flow of blood from the brain, and raising blood pressure in the blood-vessels of the brain. It is sometimes caused by organic heart trouble.
_The symptoms_ come on very suddenly in congestion of the brain. The disease may manifest itself as soon as the animal is moved out of the stall or bed, or it may come on while it is feeding. In slight cases, the animal appears excited and restless, the eyes are bright, the pupils are dilated, and the pulse beats and respirations quickened. If the animal is moving about, it may stop suddenly and show marked symptoms of a nervous disorder, such as turning around, running straight ahead and falling down. The period of excitement is usually brief and may be followed by marked depression.
The mucous membranes of the head are a deep, red color.
_The symptoms_ in anaemic conditions of the brain are loss of consciousness, stumbling, falling to the ground and sometimes convulsions.
The pig and dog may vomit. Favorable cases return to the normal within a few hours. Acute inflammatory diseases of the brain and its coverings are associated with cerebral hyperaemia or congestion.
_The treatment_ of mild cases is to give the animal quiet, well-ventilated quarters, where it can not injure itself. The animal should be first subjected to a severe diet and later given easily-digested feed. If it appears greatly excited, bleeding should be practised. Cold applications to the head should be used in all cases in the small animals. For internal treatment, purgatives are indicated. In cases of anaemia, stimulants, vigorous massage, artificial respiration and injection of physiological salt solution are indicated.
SUNSTROKE AND HEATSTROKE.--Most writers make no distinction between heatstroke and sunstroke. The latter is caused by the direct rays of the sun falling on the animal, and the former from a high temperature and poor circulation of air in the surroundings. Under such conditions, the physical condition of the animal and exertion play an important part in the production of the nervous disturbance.