424 CELLS, TISSUES, AND ORGANISMS 



communicable, age-related diseases. Of the list in the table, only 

 cirrhosis of the liver would seem to be a hopeful candidate for improve- 

 ment, in this view. Perhaps half of the mortality from cirrhosis is as- 

 sociated with alcoholism. Accordingly, control of alcoholism might cut 

 the mortality in half, but the other cirrhosis mortality would be ex- 

 pected to continue as an expression of aging. 



Table II shows the age trends among white males in the United 

 States for some of these major causes of death. The age trend is ex- 

 treme in the three most important causes of death— coronary heart 

 disease, cerebrovascular lesions, and neoplasms. 



The special case of accidents requires consideration of the factor 

 of exposure. People are not killed by falling off ladders unless they 

 happen to be up on ladders; to get killed in a speeding car you must 

 be in a speeding car. As people grow older, they tend to avoid the 

 hazardous situations that attract youth. Even though a given accident 

 may be tolerated less well by older people, the net result of less ex- 

 posure prevents accidental death from having a positive age trend 

 until very old age. 



But this matter of exposure may also explain, at least in part, the 

 age trend seen in many diseases. And insofar as this is true, we may 

 attempt to control the result of aging, if not aging itself, by controlling 

 the exposure. This is the hopeful approach that has stimulated so 

 much of the recent tremendous expansion of research in heart disease 

 and neoplasms. 



Suppose, for example, that cancer tends to develop in a given 

 tissue partly because of repeated insults or injuries not generated by 

 the tissue itself. The cases of bronchogenic carcinoma and of carcinoma 

 of the female cervix may be in point. The external force in the one 

 case may be noxious principles in the atmosphere or in tobacco smoke. 

 In the other case, physical trauma may be involved. 



TABLE II 



Death Rates of White Males in the United States, 1957 

 (deaths per 100,000) 



