Precocious old age due to the effects of disease, especially syphilis and acute infections, and to metabolic defects, which permanently damage the cells of the body, has a special interest as it supports Metchnikoff’s pathological view that old age as ordinarily seen is a result of toxic injury (vide p. 82). Hastings Gilford[43] has specially investigated premature senility, and under the title progeria has described a remarkable condition of premature senility combined with, or secondary to, infantilism. This condition was independently described in 1910 by Variot and Pironneau[44] as the senile type of nanism. In such cases it would appear reasonable to ascribe these two opposite conditions to the same toxic or other factor, the infantilism depending more on damage to the ductless glands before development was complete, and the senile changes to direct injury of the cells in the body in general.
IV
FACTORS INFLUENCING LONGEVITY
The determining factors of long life may be broadly divided into those included under heredity, environment, due functional activity, and personal habits. It is impossible to separate these factors into watertight compartments, for a certain amount of overlapping between them is unavoidable.
Heredity
The influence of heredity has often been insisted upon and is perhaps the most important factor in longevity. Out of 824 persons between 80 and 100 years of age analysed by Humphry, 406, or 49·4 per cent, came of long-lived families. Numerous striking examples of such families are on record, but a few only need be given. Roy[45] quotes the case of Dr. Iverex, who died in 1700 at the age of 104, his father at 112, his mother 107, and his grandfather 130 years, and gives four other examples of three centenarians in the same family. Another remarkable family group was that of Joseph Retas who died at Tarbes at the age of 118 in 1888, and was the son of a man aged 111 years and had a brother aged 114 years. Two centenarian twin sisters were recorded in a village near Athlone[46]; centenarian sisters and brothers are not so very exceptional. Sir Hermann Weber[47] recorded two families, in one of which the average age of ten children was over 90 years and in the other of eight children nearly 90 years.
A good stock may ensure long life in the face of adverse environment, such as town life and alcoholism; thus Dr. John Brownlee[48] showed statistically that while persons dying at the age of 51 in the average environment would have, had they lived in the country, a mean life of seven years longer, this difference was less at higher ages, and remarks that a person who has the potentiality of living to the age of 80 years has a force of life which is more or less independent of environment. Sir George Savage[49] often noted that of two aged members of the same family one was sober the other intemperate; and a good many centenarians have taken alcohol in quantities that would be too much for ordinary people.
Heredity is not an all-powerful factor, for an individual whose family history is not remarkable for longevity may greatly prolong his life by carefully correcting unfavourable hereditary tendencies. Thus the late Sir Hermann Weber, who lived to the age of 95 as the result of practising the maxims of his Prolongation of Life, mentions that his mother died of cardiac failure before she was 60 and his father at 60 from cerebral haemorrhage, and he gives other instances of the same happy result of wise management. Not unfrequently husband and wife both live to an advanced age, no doubt often as the result of favourable environment. A photograph of a married couple both 101 years old appears as the frontispiece of Sir George Humphry’s book on Old Age, and must of course be accepted; but the same cannot be said of the frontispiece to volume ii. of Sir John Sinclair’s Code of Health and Longevity (1807), representing the Hungarian husband and wife, aged respectively 172 and 164 years, who had been married 147 years.
It has been suggested that “cell-memory” by providing experience as to the proper way to behave at the different periods of life has a bearing on the coming of old age; Samuel Butler[50] argued that cells without hereditary memory of past existence at, say, 75 years, would become puzzled and so disordered as to die. Parkes Weber[51] has modified this view by assuming a failure of the wish to live on the part of the nerve cells of the brain, a want which might also be hereditary. The possession by the cells of “the will to live” would be an important factor in longevity and should be obtained by individual effort or in other words be an acquired character, though the reverse conditions such as physical mutilations,[52] often spoken of as acquired characters, are known not to be inherited.
In different countries and in different individuals the cells of the body may differ in the rate at which they live; they have, as Sir James Paget[53] said, a different “time-rate”; in some the time-rate is rapid, for example in the natives of hot climates where maturity comes early and old age at a time that seems very premature by our standard; in others the body, sometimes the mind, works slowly, is set at a more leisurely rate and therefore takes longer to run its course. In some persons this appears to be shown by a slow pulse, a characteristic that may also be hereditary.