LONGEVITY. The normal duration of life differs in different species of animals, but what factors determine the length of life of a particular species have not been discovered. Observation has taught a few generalities, that large animals live longer than small ones, that species having a numerous progeny are short lived, that those that have a long period of gestation live longer than those that have a short period of gestation, etc. Buffon, Fleuron and other naturalists have devised formula for estimating the normal duration of life, but none will apply to more than a few species or will apply to man.
To obtain a rational basis for estimating the normal duration of human life we must consider the human being possessing the in herent factors and living under the most favor able conditions necessary to complete the nor mal cycle of life. Possessing the inherent fac tors of heredity and sound constitution and living in the proper environment and follow ing a natural mode of living, the normal cycle of life falls naturally into three distinct periods, development, maturity and decline, each lasting about 30 years. That few complete the nor mal cycle is due in most cases to accidental and avoidable causes, while the few who greatly exceed the normal duration are consid ered as freaks of nature, comparable to giants in growth. An important factor conducive to longevity is the adaptability of the human or ganism to diverse environmental and living conditions. Instances of longevity are found in the torrid and frigid zones as well as in the temperate zone, in the smoke-laden atmosphere of manufacturing cities as well as in the dear atmosphere of the plains and mountains, in the ghettoes and slums and in the homes supplied with every known hygienic device. The factor of heredity is dominant as long as there is no change in environment and mode of life. A large proportion of the Jews in the European ghettoes reach old age. Transplanted to the United States and subjected to the same influ ences that shorten the lives of Americans, they deteriorate and few reach the age of their parents. The same applies to the children of Irish and Russian peasants when they come to this country. The factors especially conducive to longevity, beside the inherent factors of heredity and constitution, are outdoor active life, the activity being gauged by the physical capacity of the individual; coarse, fresh food not in excess of the needs of the body, as indicated by the sense of hunger; immediate attention to the call for the elimination of waste; sleep, the time and amount regulated by the needs of the body without regard to the clock; rational recreations on the principle that the recreation should be the antithesis of the work which made it necessary; freedom from worry and other causes of mental de pression. These factors prevail to the greatest
extent in the peasant class and in this class is found the largest number and largest propor tion of persons who complete the normal cycle of life. The peasant as he grows old gradu ally adapts his mode of life to the changing physical conditions, he works more slowly, rests more, sleeps longer and takes naps dur ing the day, eats less, and as the mental powers wane he takes a lessened interest in the events of the day and is less affected by cares, wor ries and excitement. Under the stress of mod em commercial and manufacturing activity, especially in the cities, it is becoming more and more difficult to live in such a manner that the factors conducive to longevity can be made available, and consequently premature senility and avoidable causes of disease and death are everywhere becoming more prevalent.
The statistics and records of longevity are notoriously unreliable. Records are either absent or defective. With advancing years the faculty of memory becomes weakened and the mind shows a tendency to exaggeration and the appropriation, through auto-suggestion, of incidents belonging to the lives of others, or the invention of incidents which through frequent telling become so firmly impressed upon the mind as to appear real. Forgetting their exact age they say they are near or about the next semi-decade and in a year or two they will have passed that semi-decade and are near or about the next semi-decade. Having thus reached 90 they say they are near 100, about 100 or have passed the century mark. This explains Why the census records show more persons living at the age of 80 than at the age of 79, more at 85 than at 84, more at 90 than at 89, more at 95 than at 94 and many more at 100 or over than at the age of 96, 97, 98 or 99.