JUVENTUS—_Youth_.—This succeeds to adolescence, and in its turn is replaced by manhood. If the law does not acknowledge this stage of life, it at least tacitly allows it, as being the one best adapted for the vigorous discharge of public duties; it is the age at which the greatest enterprizes have been achieved, and the most brilliant efforts of human genius fulfilled; the developement of the body having been accomplished, its powers are expanded in the production and support of intellectual energies. The action of the arterial system may be said to predominate over every other, and hence the diseases to which man is exposed in this stage of his existence are of an acute and inflammatory character. To the common observer his march of life would seem to be arrested, little material change, either of a moral or physical nature, is discernible from the age of twenty-five to thirty-five; and this period may therefore be said to occupy a part of the second great division of Aristotle to which we have alluded (the period of _Perennity_.) ÆTAS VIRILIS—_Manhood_. Youth passes into manhood by such insensible shades of gradation, that it has been considered as only a continuation of the same stage of perennity; and yet we shall find that the change from one to the other is sufficiently striking to entitle them to distinct places in the scale. Hippocrates and Galen have compared youth to the summer, and manhood to the autumn, thus insinuating that if one be less fervent, it is yet more mature than the other; and this is certainly morally and physiologically true; for although the imagination loses much of its glowing fervour, its dominion is succeeded by that of a maturer judgment; the arterial system no longer predominates over every other, its energies have been reduced, and a juster equipoise established; the diseases, therefore, to which he is liable assume a different aspect,[283] and maladies of a chronic character prevail, and thus while in the apparent plenitude of his existence is he fast journeying to his destined goal;[284] man never stands still, he is either progressing to the zenith of his strength and vigour, or he is declining from it; in vain shall we attempt to cast our anchor in the stream of life, it will alike carry away those who struggle against it, and those who yield quietly to the force of the current; the panaceas and boasted elixirs, and the many other means which have been proposed to renovate the body, are as chimerical, says Buffon, as the fountain of youth is fabulous. SENECTUS—_Old Age_. The system has now undergone a considerable change; its bony framework has acquired increased solidity and density; the vascular system is greatly abridged in the extent and subtlety of its ramifications; the muscles become less irritable, their fatty matter is absorbed, the cellular structure collapses, and the whole volume of the body diminishing.