344 Hardin B. Jones 



established as a thickening of the artery wall proportional to lipoprotein 

 elevation and duration of the condition. 



Since vascular disease is a large component of degenerative disease and a con- 

 tributing cause to other diseases, it is quite possible that exponentially-decUning 

 blood-flow capacity may in part determine the exponential pattern of increas- 

 ing incidence of overt disease other than vascular disease. 



Cancer and Aging 



Throughout adult life, cancer incidence and cancer death rate are increasing 

 exponentially; in most ways, this increase is remarkably similar to the above- 

 described increase in heart disease tendency. Armitage and Doll ('4) have 

 ascribed this property to the fact that a succession of small changes necessarily 

 precedes cancer. It is of interest to construct population samples of individuals 

 known to have died of a given kind of cancer. When this is done, the increase 

 in death rate in the cancer-destined population is remarkably like the increase 

 in incidence of cancer in the population out of which it was taken (la). Thus, 

 we can be reasonably certain that the risk of cancer is increasing exponentially 

 with age. 



In contrast to the exponentially-increasing incidence of cancer with increas- 

 ing age, individuals identified as having overt cancer have a constant death 

 risk approximately independent of chronologic age. Therefore, it is a reason- 

 able argument that changes characterizing the period prior to onset of cancer 

 may be of many different kinds, each making cancer occurrence more likely, 

 but the change representing incidence of cancer effects a single abrupt decrease 

 in life expectancy. 



It follows from this reasoning that many of the changes that accompany 

 aging may be of consequence only as they allow a drastic and irreversible 

 change into overt disease to take place. In vascular disease, the average 

 degenerative change in the walls of the artery is of less consequence 

 than the infarctions or vascular occlusive episodes that destroy peripheral tissue. 

 Death may occur as a consequence of a random occlusive event, even though 

 average changes in the arterial structure may be minimal. 



Cellular Change and Aging 



Cancer is usually considered to be an example of cellular change associated 

 with aging, very possibly upon a basis of somatic mutational change. It should 

 be noted that evidence for this is based upon an incidence of cancer expon- 

 entially increasing with age. While I, too, subscribe to this view, a similar 

 phenomenon is seen in diabetes melHtus, a disease of deletion of function. 

 It is quite possible that, in addition to changes in the quahty of cells surviving 

 Vv'ith time, certain kinds of cells may survive aging with different likehhood. 

 Shock (6) has evidence, for example, for a decline both in functional quality 

 and numbers of cells in the kidney with age. It is reasonable to explore further 

 the effects of dechning numbers of cells with age. Instances, as in the case 

 of disappearance of islet tissue in diabetes, may be observed in various tissues 

 and are represented by epilation, appearance of channels in the fingernails, 

 and disappearance of cells supplying sensory function of various kinds. These 

 cells may disappear, but we do not know why. 



