placed upon these atrophied organs. The gastric juice is secreted in less quantity, so of the pancreatic, the biliary and the intestinal juices. The lessened quantity of bile makes for constipation and the formation of gall-stones and impairs absorption, and assimilation is thus interfered with. The kidneys, the chief source of elimination of a most elaborate series of poisons, become enfeebled in their action and hence should not be overtaxed by either the quantity or the quality of the work they are called upon to perform. Finally the brain may be the part which gives way most prominently, and then we may find hemorrhages into its structure, a softening begins, and alteration in mentality which point the way to more remote and serious changes. The physiology of old age may be described briefly as a progressive diminution in all the functional activities. There is in the life of every normal individual a constant and proportional relationship between the development of parts and tissues and the natural progress toward dissolution. The function which is in most immediate relationship to the reparative power of the cells is the one which will be first affected, so soon as old age begins. The four particular acts of nutrition may be succinctly described as: first, contact of the cell with the nutritive elements; second, the phenomena by which sustenance is drawn from this material, namely, assimilation; third, the changes through which the assimilated products pass, namely, dissimilation; and fourth, the phenomena of the ejectment of the non-assimilated substances. In senescence the first change to be noted in these essential steps in nutrition is to be seen in assimilation. The reparative power of the cells is lessened and the elements of repair tend to be furnished in smaller quantities and soon pass beyond the power of maintaining cellular integrity. Next, there is a diminishing cell resistance leading to atrophy and xerosis. Xerosis (Tessier) is the normal hardening of the tissues in contradistinction to the abnormal sclerosis. With diminution in the power of assimilation there will appear modifications in the normal processes of dissimilation. The difficulties which the cell finds in securing the necessary pabulum tends toward inertia in the phenomena of metabolism. Next the products of incomplete oxidation accumulate, are made difficult to get rid of; they are more damaging to the integrity of the structure of the organ, and the tissues undergoing normal senescence are in constant peril of suffering disease changes. It is the presence of these toxins which places the physiologic processes of senility close to the line of pathology with incomplete oxidation; they tend to accumulate, to infiltrate and to work harm. Chemical changes are less active then, and more poisons form than can be thrown off; gout, rheumatism and their simulants arise. The standards for comparison in the phenomena of waste and repair are not to be formulated. The physician can not know, in the light of present knowledge, just
