119–128. Give the physiology of the bones. 119. How may the bones be considered? 120. To what may the bones be compared? 121. Give the different offices of the bones.
122. The bones are subject to growth and decay; to removal of old, useless matter, and the deposit of new particles, as in other tissues. This has been tested by the following experiment. Some of the inferior animals were fed with food that contained madder. In a few days, some of the animals were killed, and their bones exhibited an unusually reddish appearance. The remainder of the animals were, for a few weeks, fed on food that contained no coloring principle. When they were killed, their bones exhibited the usual color of such animals. The coloring matter, which had been deposited, had been removed by the action of the lymphatics.
123. The extremities of the bones that concur in forming a joint, correspond by having their respective configurations reciprocal. They are, in general, the one convex, and the other concave. In texture they are porous, and consequently more elastic than if more compact. These are covered with a cushion of cartilage. The elastic character of these parts acts as so many springs, in diminishing the jar which important organs of the system would otherwise receive.
124. The synovial membrane secretes a viscous fluid, which is called syn-o´vi-a. This lubricating fluid of the joints enables the surfaces of the bones and tendons to move smoothly upon each other, thus diminishing the friction consequent on their action.
Observations. 1st. In this secretion is manifested the skill and omnipotence of the Great Architect; for no machine of human invention supplies to itself, by its own operations, the necessary lubricating fluid. But, in the animal frame, it is 50 supplied in proper quantities, and applied in the proper place, and at the proper time.
122. What is said of the change in bones? How was it proved that there was a constant change in the osseous fabric? 123. What is said of the extremities of the bones that form a joint? 124. What is synovia? Its use? What is said of this lubricating fluid?
2d. In some cases of injury and disease, the synovial fluid is secreted in large quantities, and distends the sac of the joint. This affection is called dropsy of the joint, and occurs most frequently in that of the knee.
125. The function of the ligaments is to connect and bind together the bones of the system. By them the small bones of the wrist and foot, as well as the large bones, are as securely fastened as if retained by clasps of steel. Some of them are situated within the joints, like a central cord, or pivot, (3, fig. 26.) Some surround it like a hood, and contain the lubricating synovial fluid, (8, 9, fig. 25,) and some in the form of bands at the side, (5, 6, fig. 23.)
Fig. 25.