342 Hardin B. Jones 



of a system contributing to aging reflects the exponential increase of morbidity 

 and mortality that regularly is observed with increasing age. 



There are other examples of impairment of body function that depend 

 upon time lived and upon morbidity experience. A very general theory of 

 impairment can be argued in which morbidity leads to morbidity, and mortality 

 risk is some function of the integrated morbidity experience (la). The following 

 examples of functional disturbances may be cited to illustrate such relationship 

 between morbidity and morbidity and between morbidity and mortality: 



(a) The severity of toxic reaction usually increases more than proportionately 

 to the poison dose. 



(b) Radiation exposure induces ionization in tissues, and this morbidity 

 in turn can induce morbidity proportional to the dosage. This holds 

 both for acute effects and for life-span and carcinogenic changes. 



(c) Risks of degenerative vascular disease are proportional to the extent 

 of obesity (5). 



(d) Risks of degenerative vascular disease are proportional to the dis- 

 turbances of serum lipids in individuals followed over a segment of 

 the adult life span. 



(e) Death risks in diabetes throughout the past forty years have been 

 undergoing a progressive reduction apparently proportional to the 

 goodness of diabetic control. 



(f) Dimming of primary senses (vision, touch, pain, and hearing) is 

 associated with enhanced risks of trauma. 



(g) Susceptibility to infectious disease is believed to be directly propor- 

 tional to exposure intensity, and inversely proportional to defense 

 mechanisms such as antibody levels and antibody generating capacity 

 (lb); also, susceptibility to infectious disease can be quantitatively off'set 

 by administration of antibiotic agents. 



(h) Proportional differences in death-rate risks among population samples 

 throughout life span are related to sums of environmental and genetic 

 factors. 



Having noted examples of how morbidity and mortahty risk can be depen- 

 dent upon functional impairment, we can consider in greater detail evidence 

 pointing to a widespread interdependence of physiologic systems. In vascular 

 disease, occlusion may directly diminish blood flow in a small but critical 

 segment of the body, as in coronary thrombosis. However, even though there 

 is a measure of recovery from the acute episode, there may be a generalized 

 insufflciency of circulatory function. Changes in blood flow caused by narrowing 

 of the arterial channels may be expected to exact an effect upon function of 

 the extremities, and Dobson (2) has recently shown evidence for general 

 dependence of the body's homeostatic mechanisms upon the proportional 

 balance of regional blood flow. Thus, especially for the circulatory system, 

 we can be certain that functional changes can influence the entire quality of 

 body function. 



A similar example of interdependence of disease is in the complications 



