On turning to the digestive apparatus we have abundant marks of deterioration. The teeth fall out, the alveolar processes are ab sorbed, and the gums become hardened. In addition to these there is a change in the mus cularity of the stomach ; it has become weak, attenuated, and less contractile. The same is true of the intestines. The lacteal vessels are much fewer in number, and scarcely any lym phatic glands are to be met with. Every thing intimates that the food is less perfectly acted upon, and that consequently less chyle is ex tracted, and transmitted to the circulation.
Since, then, in these several systems, we find marks of diminution, impairment, depravation, it is not wonderful that nutrition, which is per formed by means of the materials supplied by those systems, partakes of the same characters. But as nutritive changes must have occurred in the various deteriorated parts just spoken of, it would be incorrect to say that alterations of tissue depend solely on the alterations of these systems, though they are promoted by them ; they must, in fact, have assisted each other. The altered tissues could not have been easily thus changed, without a defect in the quantity or quality of the matters out of which they are formed ; nor could the latter defects have easily occurred without some alteration in the texture of the parts employed in conveying and ela borating the nutrient fluid. It is an old saying, that the functions of the body form a circle : if this be true of their healthy condition, it is not less so of their diseases and decline.
The organs and tissues subservient to the organic life having undergone vitiation and diminution, we may expect to find equal or even greater decay in the parts which are alto gether dependent upon them, or the organs of the supplemental life. These indeed, as they are the last to be developed, are some of the first to present marks of decline, and evi dently for the same reason, viz. because they are appended to and generated by the other parts of the system, and also are more open to our observation. The body is indeed, in this respect as in many others, not unlike a poli tical community ; no great change can occur in its internal arrangements, such as a failure or derangement of its energies and resources, without a manifestation of this weakness or disorder in its foreign relations.
Let us proceed, then, to examine the ravages which are wrought by the hand of time on the organs of locomotion and sensation, in the same order in which we have traced the deve lopments and amplifications, once lavished by the self-same agent.
And first of the bones. The process of development in these parts consisted of a certain adjustment of the animal to the earthy matter, in order to give the requisite firmness, toughness, and solidity. As life advances, the phosphate and carbonate of lime are found to exceed the proportion of the cartilage and gelatine. The general conformation of the bones is less regular ; they look shrunken and worn. When handled they feel lighter, not withstanding the osseous substance is in excess; a fact, which results from the diminished quantity of the fluids, and one or two other circumstances to be mentioned presently. The processes and ridges, once so eminent and dis tinct, are comparatively effaced ; this alteration accords with the wasting and diminished exer cise of the muscles that were attached to these eminences. On looking for the lines and spaces, which are occupied in early life by cartilages or membranes, and which are visible even in manhood, we now find every trace of them vanished. Thus, the divisions between the epiphyses and shafts of the long bones, the line of union between the bones of the pelvis, and, in a still more marked degree, the sutural outlines of the bones of the head, are no longer perceptible. They are all filled up with bony deposit, and the pelvis and cranium form single bones ; even the foramina by which the nutrient arteries entered the tissue are con tracted or obliterated. The cellular structure between the tables of the cranium is removed ; and the outer plate has approximated and indeed become identified with the inner; hence we see more depressions on the surface of an aged skull.
On inspecting the internal structure of these organs, we find the cavities that contain the 0 marrow much more extensive than formerly, and the medullary tissue reduced to a con sistence scarcely exceeding that of oil. The cells also of the short bones and of the ex tremities are more expanded, and the laminae which form them are very much attenuated.