In this essay on longevity the author, an octogenarian, discusses the problem from various angles and comes to some startling conclusions. Four factors are responsible for longevity: (1) continuous flow of sex hormones, (2) mental activity, (3) transmitted diseases and (4) heredity. Mental activity, he says, is necessary for rejuvenation of the brain cells. Many priests, physicians, writers and other intellectuals live long, and more men than women reach old age because brain work required by their profession renovates their hormones. As to the third factor, two thirds of the entire medical field is covered by two groups of diseases: (1) diseases of species, chiefly of an infectious origin, and (2) diseases of individuals, mostly of a nervous character, transmitted from the father to his descendants and represented by a long array of such conditions as eczema, asthma, migraine, dyspepsia, nervous diarrhea, hemorrhoids, lithiasis and diabetes. If such functional diseases