LONGEVITY 859 would seem that brain work is not unfavourable to longevity. It is almost proverbial that statesmen and judges often reach an advanced age. Many men famous in literature and science have lived to an old age. Thus from fifty to sixty we have Tasso, Virgil, Shakespeare, Moliere, Dante, Pope, Ovid, Horace, Racine, Demosthenes ; from sixty to seventy, Lavater, Galvani, Boccaccio, Fenelon, Aristotle, Cuvier, Milton, Rousseau, Erasmus, Cervantes; from seventy to eighty, Dryden, Petrarch, Linnceus, Locke, Handel, Galileo, Swift, Roger Bacon, Charles Darwin ; from eighty to ninety, Thomas Carlyle, Young, Plato, Buffon, Goethe, Franklin, Sir W. Herschel, Newton, Vol taire, Halley; and from ninety to one hundred, Sophocles, Leeruwenhoek, Michelangelo, Titian. Physicians are often long lived : Boerhaave, Haller, Gall, Darwin, Van Swieten, Fallopius, Jenner, Cullen, Galen, and Spallanzani died between seventy and eighty years of age, and Harvey, Duhamel, Pinel, Morgagni, Heberden, and Ruysch be tween eighty and ninety; whilst the father of medicine, Hippocrates, is credited with one hundred and nine years. A valuable set of statistics have been collected by Hirt (Die Krankheiten der Arbeiter) regarding the influence of trades on longevity. An abstract of these will be found in Buck s Hygiene and Public Health, vol. ii. pp. 71, 72. The best indication of longevity in a community is given by the expectation of life from any given age. It is obtained by adding together the number of years which the entire population live from any specified age, and dividing the resulting total "years of life" by the number living at the year of age for which the expectation of life is desired (English Life Table, p. xxxiii). Thus we may find the duration of the portion of human life which an individual at any age may expect to enjoy. Such calcula tions are of great value in connexion with assurance, and indeed in all pecuniary transactions in which the value of life contingencies are taken into account. They are the bases of all systems of life assurance. Life assurance companies have now been able to collect sufficient numbers of cases of their own experience on which to find trust worthy calculations showing the expectation of life at different ages. Such tables have really been compiled from selected cases, namely, from those who have assured, and consequently differ somewhat from those compiled on the broader data obtained from the whole population. The following table, derived from both sources of informa tion, is given briefly to indicate the expectation of life, or the longevity, from various ages, reference being made for details to the article INSURANCE. The table to be read thus : a person at thirty years of age has an average expectation of living 33-3 years longer, or of attaining the age of 03 3 years. England anil Ages. Wales, l- iirr. 18:Jri-54. Combined ; Experience of 17 English .Offices, 1S43. Ages. England and Wales. Farr, 183S-.54. Combined Experience of 17 English Offices, 1843. 40-9 60 13-9 1377 10 47-4 48-36 70 8-7 8-54 20 39 9 41-49 80 5-1 478 30 33 3 34-43 90 2-9 2-11 40 267 27-28 95 2-2 1-23 50 201 20-13 What are the physiological conditions in the human being that determine longevity ? In the first place, there is the influence of heredity. Certain peculiarities of tissue arc transmitted from parent to offspring that determine whether or not the tissue will remain for a lengthened period of time in a normal condition, or whether it will quickly yield to external influences and take on an abnormal action. As the life of the body is really the sum of the lives of its constituent parts, or in other words, of the cellular elements composing it, it is evident that anything affecting the healthy action of these elements will affect the life of the body as a whole. In some individuals the tissues have what may be termed a hereditary taint, by which is meant a want of stability, so that they pass readily from a normal into an abnormal condition ; and this is unfavourable to longevity. In the next place, even healthy tissues capable of resist ing ordinary influences may be unable to resist long- continued unfavourable conditions. In course of time slow changes begin in the tissue ; these in turn affect the organ in which the tissue exists, and the organ, by improperly performing its functions, injures the organism. Thus it is that habitually breathing an impure atmosphere, eating improper food, saturating the body with drugs or with alcohol, over-exerting the nervous system by excitement or prolonged brain-work or worry, and sexual excesses de bilitate the body by working slow but sure changes in the tissues which will inevitably tell upon the longevity of the individual. But even in the most favourable conditions there seems to be a limitation to the healthy action of tissues, and old age comes on. Whether this is or is not the result of long hereditary transmission it is not of much practical import ance to ask, as it is a state of things all flesh is heir to. But, if it be hereditary, as is highly probable, there is the satisfaction of knowing that hereditary states can be slowly influenced by individuals living in the best possible con ditions and transmitting the influences of good moral and physical hygiene. If bad hereditary qualities are trans mitted, good qualities have even a better chance of being perpetuated, as they favour the individual in the struggle for existence. Thus a race which has a low degree of longevity may acquire, by persistent attempts to live in the best conditions, a long average duration of life. This is also true, though to a less extent, of an individual life. Each tissue has a life of its own ; it is developed, reaches maturity, declines, and dies. It may be replaced by successive generations of similar tissues, but the power of reproduction of tissue becomes weakened, and by slow degrees the tissue may disappear, or it may become so altered as to be quite unlike what it was at first. By these tissue-changes functional changes of great importance to the body are brought about. Thus, as age comes on, the blood becomes poorer; respiration is less active; the vital capacity of the chest, that is the working-quantity of air, is diminished ; the temperature of the body is slightly increased, so that the aged are more sensitive to cold ; the digestive organs are less vigorous ; the walls of 4 the arteries become hardened by earthy matter, and lose their elasticity ; the veins become dilated, and the circulation is not efficiently performed ; the teeth decay and disappear ; the cartilages become calcified and hard ; the skin is shrivelled and dry, and cutaneous respiration and excretion are less perfect; the hair whitens or falls off; the stature and the weight diminish. By and by muscular movements are less energetic and less precise ; the hands tremble and the head shakes ; and there is a tottering gait. The cartilages of the larynx ossify, the vocal cords lose their elasticity, and the voice becomes a shrill treble. Then the involuntary muscular tissues are affected so that the bladder is less powerful and defsecation is feeble. The transparent media of the eye become dimmed, the near point of vision is pushed back so that the old man becomes presbyopic, or far-sighted, and the power of accommodation, or focussing of the eye, is entirely lost ; the delicate mechanism of the drum and bones of the ear is impaired, so that deafness results ; and even touch becomes less delicate. Slowly the intellectual faculties become weakened, the emotions are blunted, and the memory becomes by degrees less
