Heart
3 of the 7 encyclopedias on this shelf carry an entry for Heart. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
the muscle that forces the blood to circulate. In man it is a cone shaped organ lying apex downward in a slanting position in the left side of the chest between the lungs. The point of the heart is opposite the space between the fifth and the sixth ribs. The base is opposite the second rib. It is a strong muscle with four cavities--two receiving and two expelling. The blood of the body drains into one side of the heart and is forced through arteries into the lungs. From the lungs it draws back into the other side of the heart and is squeezed out or driven to all parts of the body only to drain back as before. For an account of the auricles, ventricles, veins, and arteries, and especially of the valves which guard the doorways and prevent the backset of the blood, though permitting it to go forward, a physiology should be consulted. The heart is about the size of its owner's closed fist. Its action is due, it is held by high authority, to the influence of the blood upon the muscles. An accumulation of blood seems to exert an influence, electric or nervous, or whatever it may be, upon the muscular wall of the heart, causing a powerful spasmodic contraction which brings the walls of the cavity together and drives the blood out upon the next stage of its journey. The left side is the larger and more powerful, being charged with the circulation of the blood in the system. The contractions or beats of the heart are made at the rate of about seventy-two per minute. Some idea can be had of the work it must do when we recall that the blood weighs about one-twelfth as much as the entire body, and that it is pumped over and over, the entire amount passing through the heart in from fifteen to thirty seconds. It is hard to realize that while one slowly counts thirty, the blood has run swiftly from one's great toe to the heart, been pumped to the lungs, purified, drained back to the heart and driven to the great toe again, nor should it seem surprising that the action of the heart and the circulation of the blood were not understood by the most skillful surgeons until long after the discovery of America, not in fact till the more important American colonies were well underway. The heart of cold-blooded animals is comparatively small and feeble in action. The heart of the frog has two auricles and but one ventricle; that of the fish one auricle and one ventricle. See Harvey ; Lymph; Blood ; Circulation
Collier's New Encyclopedia (1921)
in human anatomy, the central organ of circulation, inclosed in a membrane, the pericardium, and lying between the two layers of pleura, the mediastinum, with the base directed upward and backward to the right shoulder, and the apex downward and forward between the fifth and sixth ribs, and to the left. The under side is flattened and rests on the diaphragm, the upper rounded and convex, formed by the right ventricle and partially by the left; above these are the auricles whose appendages project forward, overlapping the root of the pulmonary artery, the large anterior vessel at the root of the heart, crossing obliquely the commencement of the aorta. The right is the venous side of the heart, the left arterial. The right auricle is larger than the left, and more complex in structure; it has two valves, the eustachian and the coronary. There is not the same pyramidal form in the left ventricle as in the right; the apex of the heart is also the apex of the left ventricle, and therefore larger than the right. The valves of the right ventricle are the tricuspid and semilunar; of the left the mitral (bicuspid) and semilunar. The auriculoventricular opening connects the auricles and ventricles, and in connection with the ventricular valves we have the columnæ corneæ, of which there are three sets, and the chordæ tendineæ. There are three layers of fibers in the ventriclesthe external, middle, and internal-their peculiar spiral arrangement causing the tilting forward of the cardiac apex. The fibers of the auricles are in two layers - the external and internal; and the left auricle is thicker and more fleshly than the right. From the right ventricle arises the pulmonary artery, conveying the venous blood to be aërated in the lungs; the infundibulum is a prolongation of the anterior wall. The left auricle contains the four pulmonary veins returning the blood to the heart, thence to the left ventricle, and thence to the aorta, to be distributed to every part of the body, returning by the superior and inferior vena cava to the right auricle. In the lowest animals we have no blood-vessels, every part absorbing nutritious fluid for itself; the lower Entozoa, and even the embryo in man in its early stage, are examples. Among the higher reptiles, we find the circulation approaching that in birds and mammals, till we get the double heart, as in man.
An Encyclopaedia of Occultism (1920)
It is said in Ecclesiates that the heart of the wise is at the right side, the heart of the foolish at the left. But this saying must be placed in the same category as that of Jonas, who said of some of the Ninevites that they did not know their right hand from their lelt-that is, they could not distinguish good from evil.