These have been much less frequently observed in the lower animals than in man. The anomalies observed in mammals include the following: The displacement of the heart to the right side of the chest; displacement entirely out of the chest (ectopia cordis); permanent communication between the right and left auricles (cyanosis); entire absence of heart; two hearts; one common ventricle communicating with two auricles as in reptiles; three ventricles; only one auricle; absence of one or several valves; absence of the pericardium; variations in the mode of connection of the heart and large vessels, etc.
Displacements of the heart have been especially studied by Hering on calves. The breast bone remained as originally developed in two lateral halves, and the heart remained outside connected with the interior of the chest only by its large vessels. The heart thus exposed and covered only by its investing membrane (pericardium) afforded an excellent opportunity to study its action, of which Hering freely availed himself. Animals affected in this way survived their birth but a very short time. An approach to this condition was thirty years ago made familiar to the medical world in the person of M. Gouz, a German mechanic, the movements of whose heart could be easily watched through a fissure in the breast bone.
Permanent communication between the two auricles. Pervious foramen ovale. Cyanosis. Previous to birth there is an opening between the right and left auricle, allowing the blood to flow from the former into the latter in place of, as in after life, descending into the right ventricle and thence circulating through the lungs. At birth this is contracted, and in a few days is completely closed in accordance with the new life, which demands that all blood must circulate through the lungs in order to its æration. Sometimes this fails to be effected, and venous blood from the right side of the heart continues to mix with arterial in the left, deteriorating it in quality and unfitting it for nutrition, secretion, calorification, and other essential processes. The semi-venous blood circulating in the arteries gives a bluish hue to the visible mucous membrane, hence the name of the blue disease. This blood is unfit for sustaining the vital changes essential to the production of animal heat, so that the animal suffers from coldness of the surface and extremities, staring coat and general unthrifty appearance. Such subjects grow badly, and refuse to lay on flesh, but are said to arrive at maturity in some instances and to have their imperfection recognized only because of the short breathing, and irregular heart’s action when subjected to exertion. A heart murmur preceding the first sound of health is usually present, as in anæmia.
Drs. Abernethy and Wardrop draw attention to the frequency of previous foramen ovale in the human subject in connection with pulmonary consumption, and opine that it is reopened as a consequence of this disease. The coincidence has not been observed in the lower animals, though if it were found to exist the question would arise whether the deterioration of the blood and general health in open foramen ovale did not also favor the deposit of tubercle in the lungs. When from deficient ventilation the atmosphere and blood become impregnated with carbonic dioxide the production of tubercle in man or in animals is correspondingly frequent.
The subjects of previous foramen ovale die young or prove worthless when they arrive at maturity. Nothing can be done to ameliorate the condition.
HYPERTROPHY OF THE HEART.
Simple, eccentric, concentric. Ventricles chiefly affected. Causes, increased functional activity, from obstruction to the circulation, or continued extra exertion. Right ventricular hypertrophy-obstruction in the pulmonary circulation; left ventricular hypertrophy-obstruction in the systemic. Auricular hypertrophy-insufficiency of the auriculo-ventricular valves. Pericarditis as a cause. Abnormal weights. Symptoms, beats more forcible and prolonged, 1st sound low, prolonged, 2nd sound clear, often doubled, increased dulness on percussion, diagnostic signs of hypertrophy, dilatation and a combination of the two. Simple hypertrophy rarely dangerous, with dilatation grave, threatens congestions and apoplexies. Treatment, rest, laxatives, sedatives, in irregular heart action digitalis, arsenic.
An enlargement of the heart from increase of its muscular substance is by no means uncommon in the horse. It may exist without any change in the capacity of the cavities of the heart (simple hypertrophy) or it may be associated with dilatation of one or more of these cavities (hypertrophy with dilatation;—eccentric hypertrophy). A third variety has been described in which the capacity of the cavities is decreased but Cruveilhier and Budd have satisfactorily shown the nonexistence of this condition except as a congenital deformity.
It is in the ventricles that the increase is chiefly observed, the reason of which is to be found in the causes of the malady. These usually consist in some obstruction to the circulation such as chronic congestions in the lungs or elsewhere, rupture of air cells in the lungs, tuberculous and other abnormal deposits in the chest and elsewhere, tumors which by their position interfere with the circulation through the larger vessels, and the like. Where by some such cause the blood is impeded in its outward course, one or both ventricles are called upon to contract more vigorously to force a sufficient amount of blood onward and in accordance with the inherent adaptability of the animal economy, there takes place an increase of the muscular walls of the ventricle proportionate to the required energy of the contractions. The condition then is essentially due to a more active nutrition and growth of the muscular substance and finds its exact parallels in the well-developed legs of the ballet dancer or the brawny arm of the blacksmith. All alike occur in accordance with a general law that whenever there is habitually demanded of any organ an unusual activity of function, which stimulates without exhausting its power, nature adds to the active element of such organ till the required labor can be accomplished without the overwork of any particular part.
Keeping this in view we can easily explain the increase of one part of the heart without immediate implication of another. The ventricles are more commonly enlarged than the auricles because upon them devolves the work of overcoming the obstruction, whether this exists in the lungs or the system at large. The auricles fulfill little more than a passive function in receiving the blood from the veins during the contraction of the ventricles and allowing it to pass down into these when their relaxation takes place. The closure of the auriculo-ventricular valves during the ventricular contraction protects the auricles from the internal tension to which the lower part of the heart is subjected and thus all tendency to increase is obviated.