The ideas of the etiology and pathological processes through which we journey,--from a condition of health and good feeling to one of disease, miserable feeling, and death,--as described in, or rather as they control the sentiment and policy of, this work, are such as have been followed by Hutchinson, Fothergill, Beale, Black, Albutt, and Richardson, so that if I have totally ignored the old conventional systems, with their hide-bound classification of diseases to control the etiology, I have not done so without some reliable authority. In studying the etiology of diseases we have, as a rule, been content to accept the disease when fully formed and properly labeled, being apparently satisfied with beginning our investigation not at the initial point of departure from health, but at some distant point from this, at the point where this departure has elaborated itself, on favorable ground, into a tangible general or local disease. As truthfully observed by T. Clifford Albutt: "The philosophic inquirer is not satisfied to know that a person is suffering, for example, from a cancer. He desires to know why he is so suffering,--that is, what are the processes which necessarily precede or follow it. He wishes to include this phenomena, now isolated, in a series of which it must necessarily be but a member, to trace the period of which it must be but a phase. He believes that diseased processes have their evolution and the laws of it, as have other natural processes, and he believes that these are fixed and knowable." To do this, the physician must travel beyond the beaten path of etiology as found in our text-books. He must follow Hutchinson in the train of reasoning that elucidates the pre-cancerous stage of cancer, or tread in the path followed by Sir Lionel Beale, in finding that the cause of disease depends on a blood change and the developmental defect, or the tendency or inherent weakness of the affected part or organ; to fully appreciate the inherent etiological factors that reside in man, and which constitute the tendency to disease or premature decay and death, we must also be able to follow Canstatt, Day, Rostan, Charcot, Rush, Cheyne, Humphry, or Reveille-Parise into the study of the different conditions which, though normal, are nevertheless factors of a slow or a long life. We must also be able to appreciate fully the value of that interdependence of each part of our organism, which often, owing to a want of equilibrium of strength and resistance in some part when compared to the rest, causes the whole to give way, just as a flaw in a levee will cause the whole of the solidly-constructed mass to give way, or a demoralized regiment may entail the utter rout of an army. As described by George Murray Humphry, in his instructive work on "Old Age," at page 11:--