4o8 POPULAR SCIENCE MONTHLY. 



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 inter- 

 fered 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 relation- 

 ship 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 diminu- 

 tion 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 com- 

 parison in the phenomena of waste and repair are not to be formulated. 

 The physician can not know, in the light of present knowledge, just 



