The gain in life expectancy in the last onehundred years was achieved mainly through the conquest of transmissible diseases. Life expectancy in middle age has not, however, improved appreciably because the reduction in the infectious diseases was counterbalanced by an increase in the non-transmissible conditions, especially the cardiovascular disorders. This situation results in a great loss in years of life. There is every reason to believe that changes in daily habits of living and improvement of environmental conditions could diminish the corresponding mortality, morbidity and invalidity...