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. Roy45 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 Athlone46; centenarian sisters and brothers are not so very exceptional. Sir Hermann Weber47 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 Brownlee48 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 Savage49 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 Butler50 argued that cells without hereditary memory of past existence at, say, 75 years, would become puzzled and so disordered as to die. Parkes Weber51 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 Paget53 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.

Of the hereditary factors most concerned in longevity the inherent vitality of the central nervous system is the most essential; physiological death in man and the higher animals is probably due to failure of the cells of the brain, which do not multiply after birth and are less capable of rejuvenescence than those of the other organs. The integrity of the cardio-vascular system is also most important; in Sir William Osler’s54 words much depends “on the quality of arterial tissue (vital rubber) which the individual has inherited.” According to Sir Clifford Allbutt55 there are two modes of hereditary transmission of arteriosclerosis, the direct and the indirect; the direct which he calls decrescent or primary, consisting in an original frailty or toxic susceptibility which like other peculiarities may run in families; and the indirect or hyperpietic, a secondary event due not to inherent taint in the arterial walls but to metabolic changes causing high arterial pressure; it is in such families with hereditary high blood pressure that cerebral haemorrhage occurs in one generation after another about the same age (65–70). In examining people the discovery of a blood pressure low for their age often justifies, in the absence of any pathological condition, the suggestion that the family is long-lived. The frequency of cardiac hypertrophy (43 per cent of Councilman’s cases), even though it be a pathological condition, shows that its reserve power is good. Death among the aged very commonly depends on some morbid change in the cardio-vascular system; thus at the Royal Hospital, Chelsea, Majors R.J.C. Thompson and R.E. Todd56 found that among 169 deaths of pensioners with an average age of 77·2 years the largest number 64, or 38 per cent, were due to this cause; lesions of the respiratory system, pneumonia, and bronchopneumonia, coming next with 41 deaths, or 24 per cent, malignant disease being responsible for 22, or 13 per cent. The nervous and circulatory systems are intimately correlated with each other, disorder or disease of one, particularly of the cardio-vascular system, exerting an evil influence on the other. In a negative manner weakness of the digestive system may favour longevity by preventing the excesses which vigorous individuals may for a time at any rate indulge in with impunity; but as a rule the digestion of the long-lived is good.

The first-born is significantly handicapped, as Karl Pearson57 has shown, and more subject to tuberculosis, insanity, and criminality. But out of 71 centenarians analysed by Sir George Humphry 17, or 24 per cent, were firstlings, and 24 per cent of 824 persons between 80 and 100 were first-born. It must be remembered that first-born are more numerous than any others, and some of the above were only children. The most frequent position in the family among these 895 old people analysed by Sir George Humphry was the third.

Environment

The influences included under the head of environment are numerous, and this factor cannot be entirely separated from that of heredity, for environment may favour and shape hereditary characteristics. The subject of the harmony and the want of harmony existing between man and his surroundings is so vast that it is possible to touch on a few only of these aspects.

The average length of life varies in different countries; a temperate or moderately cold climate is conducive to a slower development of maturity and so to a longer life than tropical regions. The Balkans, Greece, Scandinavia, the Pyrenees, California, and small islands are considered favourable to longevity. A high elevation has been regarded as an important factor, and the great age of the monks of Mount Athos has been thus explained, though other influences, such as simplicity of life, may well play a part. Switzerland, however, does not conform to the view that a high elevation confers long life on its inhabitants. From observations around Dijon Noirot58 drew up a scale showing that the elevation above the sea and length of life rose together. National habits have a bearing, and this may help to explain the longevity of the Jews, who follow the Mosaic laws of health, and why the French appear to be more long-lived than the Germans. The long-continued persecution and hard life that the Jews have undergone has led to the survival of the fittest and a hereditary factor. The former simplicity of the Russian peasants would also provide a reason for their reputed longevity (one centenarian in every thousand). In Ireland, though much depleted by migration of young adults, the absolute number of centenarians is very high; in 1888 there were 208 such deaths, or 43 per million living; in the ten years 1911–20 inclusive there were 1030 centenarian deaths, or about 23 per million living; and the Registrar-General, Sir William J. Thompson, kindly informs me that in 1921 there were 314 centenarians living in a population of 4,496,000, or about 70 per million of the population. It seems probable that this is the outcome of a simple life. In England and Wales the number of centenarians is both relatively and absolutely less; in 1887 there were said to be about 2 and the 1911 census returns showed 3·6 living centenarians per million of the population; the return of the 1921 census is not yet available. In the ten completed years 1910–19 there were 691 centenarian deaths, or an average of 69 annually among a population averaging about 35 millions—about two per million living. In California there are, according to Laurent,59 300 centenarians in a population of three millions, or 100 per million, the extremely favourable climatic conditions accounting for this high ratio. In the same country there is a difference, much to the advantage of the rural inhabitants, between the prospect of longevity in the towns and in the sparsely populated districts. From their open-air life agricultural labourers provide the largest percentage of long lives.

Improved Conditions of Life.—There is good evidence that the average expectation of life has improved in this country during the period that increasing attention has been paid to sanitation. This is shown by the tables of the Registrar-General. For most of the following information I am indebted to Dr. T.H.C. Stevenson of the General Register Office, Somerset House. In 1838–54 the expectation of males at birth in England and Wales was 39·91 years, in 1901–10 the male and female expectations at birth were 48·53 and 52·38 years respectively, and the latest available expectations at birth (English Life, Table No. 8, Supplement to the Seventy-fifth Annual Report of the Registrar-General, Cd. 7512) are 51·6 for males and 55·35 years for females. But the expectation is probably considerably more now, as the death rates have fallen appreciably since 1910–12. The Prussian male expectation of life at birth has increased from 35·38 years in 1867–77 to 46·43 in 1906–10;60 and the Swedish61 expectation of life at birth from 39·5 years in males and 43·6 years in females in 1816–40 to 54·5 and 57 years respectively in 1901–10. In North America62 there has been a fall in the death rate in every age group in 1920 as compared with 1910. The increased expectation of life has been especially prominent in early and adult life. Examination of the Registrar-General’s census returns from 1851 to 1911 show that although there were more persons per million living between the ages of 55 and 75 there were less above the age of 75 at the end than at the beginning of this 60-years’ period. It has been suggested that the increased survival in the earlier period of old age is due to the saving of life in infancy and that, as these lives are not prolonged above the age of 75 or so, the diminished proportion of persons living to become octogenarians is explained (H. Weber).

The influence of past diseases is perhaps most conveniently considered in connexion with environment. As infection must necessarily impair the vitality of the cells of the body, either temporarily or permanently, it would be natural to expect that those who live to a great age would show a remarkably clean bill of health. This is often true. But it is at first sight rather disconcerting to find that nearly half of the 824 persons between 80 and 100 years of age analysed by Sir George Humphry had had severe illnesses at one time or another; many of these, however, were acute infections. It is noticeable that 85 per cent were free from rheumatism in the hands (selected as a convenient test in his collective investigation), which in the light of present opinion that arthritis is the result of a focal infection would appear to show that these old people are remarkably free from chronic disease. Long-continued infection or intoxication would be a far more potent factor than a transient illness in producing permanent change in the cells. A short acute infection would cause changes in the cells which might, like those of fatigue, be temporary and recoverable. Saundby’s63 dictum may be accepted as fairly accurate, exception being made for peripheral mutilations, namely, that those only can expect to live to extreme old age who at the age of 60 possess bodies free from disease. But critical examination would no doubt show that focal infections become increasingly frequent as the years go on; this is particularly true as regards oral sepsis; after two years’ experience of 500 pensioners at the Royal Hospital, Chelsea, Thompson and Todd have never seen a tooth in a healthy condition there. It is noteworthy that dental disease seems to have become common with the advent of civilization, as judged by examination of ancient skulls, though the loss of teeth is an accompaniment of the bony changes in old age, and very old people seldom have more than a few teeth left. On the other hand, an acute illness is often the apparent starting-point of old age; there may be a long and imperfect convalescence due to persistence of infection, or deterioration may be due to auto- or hetero-suggestion (vide p. 48).

The influence of syphilis, whether congenital or acquired, is one of the most important in the prevention of healthy longevity; it not only directly disables and kills, especially in infancy and in the fifth decade, but it damages the vitality of the cells thus producing degeneration and premature senility, and favours secondary infections.

It is clear that for the preservation of health detection of disease in the earliest stage is all-important, and that this can be attained by periodic examination by a medical man; but obvious though this may be, the average man waits to call in a doctor until he knows that he is ill. Timely advice as to methods of life, food and drink, occupation, or environment would often prevent disease and premature death. In 1913 the Life Extension Institute was founded in New York for such periodic examination and report, and the Life Assurance Companies, finding that persons so examined showed, at any rate for some years, a death rate lower than that anticipated, gave it financial support.

Functional Activity

As is well known, disuse leads to atrophy, and biologically conditions rendering an animal’s supply of food extremely easy and safe are followed by atrophy of the parts no longer necessary in a state which may thus come to border on parasitism; in an extreme degree this result is shown in barnacles (degenerated crustaceans) and ascidians (degenerated vertebrates). In man the cessation of an active life on retirement to the country, described by Samuel Johnson as “a kind of mental imprisonment,” or the sudden acquisition of wealth, often exerts a most evil influence; for if the whole body is no longer kept in a condition of functional activity, those parts allowed to remain relatively idle begin to degenerate and atrophy; loss of function means a diminished blood supply and nutrition, and so degenerative atrophy. According to Laurentius “nothing hastens old age more than idleness.” James Easton,64 who collected 1712 records of centenarians, many of them open to criticism, endorses Hufeland’s dictum that no idler has ever attained to a remarkably great age; and Sir Thomas Browne’s65 quaint injunction “Dull not away thy days in sloathful supinity and the tediousness of doing nothing” is old but true wisdom.

The axiom that disuse leads to atrophy applies perhaps even more to mental activity, for resting and rusting of the brain slow the pace of the whole body, whereas an alert mind can exist in an infirm body. There is no doubt that occupation with a strong desire to live for the accomplishment of a definite purpose exerts a most beneficial influence, and there have not been wanting some, such as Karl Marx, who have preached that old age is in great part a matter of will. Speaking of the circle in which Madame du Deffand moved Lytton Strachey66 says “They refused to grow old; they almost refused to die. Time himself seems to have joined their circle, to have been infected with their politeness, and to have absolved them, to the furthest possible point from the operation of his laws. Voltaire, d’Argental, Moncrif, HÉnault, Madame d’Egmont, Madame du Deffand herself all lived to be well over eighty, with the full zest of their activities unimpaired.” Want of this joy in life necessarily engenders carelessness and neglect of personal hygiene, and loss of the power to react to the environment. As the years advance and the younger generation come up, the suggestion that “his day is done,” that he has had his innings, and that it is time for him to step aside, is made to the senior not only by his family and his juniors—hetero-suggestion—but by himself, and he may then, after the modern fashion, get into the habit of repeating mentally “I am getting older and older every day.” A slight illness or incapacity may be magnified into a conviction that the end is near, and as a result of the loss of self-reliance a state of increasing invalidism is established and becomes progressive without any other cause. Just as a fall, an exacerbation of rheumatic pain, a slight operation or indisposition, necessitating rest in bed for a short time, may be followed by a functional loss of power in the lower extremities, so a more general suggestion of failing powers may lead to mental deterioration. Thus too often a man’s last occupation is to shorten his existence and make it miserable. Finot,67 who rather optimistically believes that man should be able to live 150 years, regards this poisonous auto-suggestion as one of the factors that prevent such an achievement. Observation of contemporaries suffering from premature senile changes, due to pathological factors, may no doubt stimulate this destructive form of auto-suggestion. There is therefore a basis for the idea68 attributed to the late Lord Rhondda that old age was a transferable disease, and for his avoidance, as far as possible, of the society of the aged on account of the risk of contagion. Association with the young keeps one more or less of the same age, very probably by suggestion to the unconscious, or in Oliver Wendell Holmes’s words “While we’ve youth in our hearts we can never grow old.” From experience at the Royal Hospital, Chelsea, where there are 500 pensioners, Thompson and Todd69 are convinced of the powerful factor of lowered mentality due to loss of self-reliance, self-respect, and the instinct of self-preservation in inducing premature senility, and have been most successful in counteracting this by antidotal suggestion conveyed by cheerful chaff and by the avoidance of sympathetic condolence.

In addition to the joie de vivre a happy disposition that thinketh no evil, has no jealous suspicions, and is free from the tendency to worry has an important influence in keeping the mind and body young. The power of detachment from work and anxieties, as if the mind were fitted with thought-tight compartments, is a valuable asset in maintaining vitality unimpaired; this was a trait in Gladstone and Kitchener.

Professional men who retain their offices as in the Church, the Civil Government, the Bar, tend to live longer than business men who retire to leisured ease after a strenuous struggle. B. Yeo’s70 analysis of 42 Bishops and Deans, 49 Judges, and 188 Peers, showed that in all three classes the average duration of life was practically the same, namely, 72 years. Among churchmen mention may be made of Cardinal de Salis (110), Gregory IX. (100), AbbÉ Maignon (100), Martin Routh (100), for 63 years President of Magdalen College, Oxford, thus surpassing the more modern instance of Edward Atkinson, aged 96 years, for 59 of which he was Master of Clare, but not that of Laurence Chaderton (1536–1640) who, after being Master of Christ’s College, Cambridge, with great success for 38 years, survived for 18 years and became a centenarian. There are some remarkable examples of artists retaining an active life to a very advanced age, such as Titian, Giovanni Bellini, Michael Angelo, Sidney Cooper. Politics often keep men busy and active to an advanced age, and the names of Palmerston, Brougham, Lyndhurst, the octogenarian premiers Gladstone and Clemenceau, Strathcona, Sir Charles Tupper naturally come to one’s mind. In the legal profession Chief Justices and Judges can retain their seats and so keep up their vigour long past what is regarded in some walks of life as the retiring age. Sir Edward Coke (82), Lord Mansfield (89), Lord Brampton (90), Lord St. Leonards (93), and Lord Halsbury (97), are examples in point. Within recent years there have been two octogenarian Lord Mayors of London, Sir Thomas Crosby (in 1911), and Sir John James Baddeley (1921); the first created a record by being the first medical man to hold this office, and Sir John Baddeley celebrated his year of Mayoralty by bringing out a beautiful historical account of Cripplegate.

From the inevitable exposure to infection and worry the medical fraternity is generally considered to rank low in the professions as regards longevity, but it is easy to point to exceptions especially among those whose mental vigour made them prominent in their own and in one instance for all time. Hippocrates is variously stated to have died at the ages of 85, 90, 104, or 106 years with the words “I leave behind me two great physicians, temperance and frugality.”71 I have references to 43 medical centenarians for 18 of which, including the record of W.G. Meade, physician at Tunbridge Wells and buried at Ware, Herts, in November 1652, aged 148¾ years, I am indebted to my friend Mr. R.R. James. The only one that I knew personally was Sir Henry Pitman, for 31 years (1858–89) and until his 82nd year Registrar of the Royal College of Physicians of London. Among the others Dr. de Bossy of Paris may be mentioned as the son of a centenarian. From analysis of 2113 eminent medical men Drinkwater72 found that the average age was 67 years, or considerably above the average age of the male population over 21 years, which was estimated at 59 years, and that 627 or nearly a third of them all were between 71 and 80 years of age.

But the examples given of mental activity late in life, and they could easily be multiplied,73 are exceptions to the rule that the majority of men begin to fail in their work between 60 and 70. This no doubt is because most septuagenarians suffer in greater or less degree from pathological old age. In the case of the healthy vigorous man enforced retirement at the age of 65 or 70 is not to the advantage of either the retiring victim or the community, for it restricts his opportunities for production and useful activities guided by ripe experience. To quote examples of epoch-making work done by men long past the age when the majority have lost originality, initiative, and elasticity of mind: Galileo, Newton, Charles Darwin, Sophocles, Voltaire, MoliÈre, Goethe, Michael Angelo, and Titian, made original and lasting contributions to science, literature, and art long after fifty. Morgagni’s famous De Sedibus et Causis Morborum, brought out when he was 80, and the Commentaries of W. Heberden (aged 91), published posthumously, represent the accumulation of many years and so cannot be fairly quoted as examples of ability persisting into late life. Rules and regulations must, however, be based on what is best for the majority and hence, though the exceptions are prominent and regrettable, the age limit of 65 to 70 must at present be accepted as generally advisable for otherwise permanent appointments.

Although functional activity maintains the tissues in a state of health, it is not an infallible panacea for the prolongation of life; in the first place the danger of overwork and excessive fatigue must be borne in mind. While the attractive suggestion that excessive functional activity leading to extreme hypertrophy may exhaust the vitality of the tissues and lead to atrophy, may not be borne out by the examples quoted in its favour, such as the occupational neuroses and atrophy of the upper arm muscles in hammermen and file-cutters, there is some reason to retain a belief that this sequence of events may occur, for example in dilatation of the extremely hypertrophied hearts seen in long-continued high blood pressure, renal disease, and valvular lesions;74 but even here the possibility of other degenerative changes, due to toxaemia, must be borne in mind. Further, functional activity while keeping the cells of the body in a healthy state depends on their structural integrity, and this in its turn is the outcome of the modifications due to environment, and possibly of the inborn lease of vitality. So that although an active life may within limits prolong life, there are many instances in which, from extrinsic pathological influences or inherent inadequacy, it fails to do so, and a man becomes unequal to the demands of his position.

Personal Habits

All experience, medical and lay, such as is embodied in Cornaro’s oft-quoted memoirs, Leonardus Lessius’s Hygiasticon or the right course of preserving life and health until extreme old age (1613), George Cheyne’s Essay of Health and Long Life (1724), Metchnikoff’s orthobiosis, and the Arabian proverb of the ninth century, quoted by Lacassagne,75 that “the greatest dangers for an old man are a good cook and a young wife,” is in agreement as to the immense importance of strict moderation in indulging the appetites for the prolongation of life. The life histories of centenarians show that they have usually been small eaters, especially of meat. This is generally explained in terms of minimizing toxaemia, and it has been said that “man does not die, he kills himself” (Montaigne) and more graphically, if coarsely, that “he digs his grave with his teeth.” In some lower forms of life, such as the planarians (Child), partial starvation and the resulting reduction lead to rejuvenescence and so to the inhibition of the onset of senescence; hibernation has somewhat the same effect, though perhaps this might be partly explained as merely starvation during prolonged sleep. The question has often been raised whether partial starvation in man has any such positive influence, and unprofessional “cures” on these economical lines have not been unfashionable. It might indeed be argued that the Allen treatment of diabetes, in which starvation is followed by increased carbohydrate tolerance, depends on a certain degree of rejuvenescence. Cures consisting in purgation may act by partial starvation as well as by obviating toxaemia. After a period of starvation a normal person may become heavier than before, and his general health be improved. But in the present state of our knowledge and in the light of the dangers of starvation the further investigation in man of this problem is one that demands serious hesitation.

As to the bad influence of alcohol on longevity there can be no reasonable doubt. Alcohol is a protoplasmic poison causing degenerative changes in the cells and reducing the resistance to infection. A collective investigation undertaken by Sir Isambard Owen76 showed that there were very few hard drinkers among the long-lived, and Sir George Humphry concluded that the characteristics of the aged included temperance; among 46 centenarians one, and among 73 men over 90 one confessed to taking too much occasionally, and out of 298 men between 80 and 90 years of age 45, or 15 per cent, were classified as taking much alcohol. That such exceptions occur is explicable by great inherent vitality. It has been said that “wine is the milk of old people,” but from his experience of the hygiene of the elderly Sir Hermann Weber was not in sympathy with this view, and he pointed out the weakness of the popular idea that the moderate enjoyment of alcohol was harmless; for so-called moderate drinking is in reality often immoderate indulgence for the individual, and most of us must have recognized from observation that long-continued though moderate use of alcohol is followed by premature deterioration. The proverb vinum lac veneris and the tendency that alcohol has to lead to incontinence and so to venereal infection may be borne in mind in considering its influence on longevity. As a medicine alcohol has its occasional use, and though it may be a food it is an expensive one.

Smoking among centenarians was specially investigated by Sir George Humphry, who found that among 19 male centenarians 8 smoked much, one a little, and 10 not at all; while out of 30 female centenarians 4 smoked much, 2 moderately or little, and 24 not at all. There is no doubt that with advancing years there is commonly a relative loss of tolerance for tobacco, so that unpleasant symptoms ranging from cardiac extra-systoles, through abdominal pain, to tobacco angina, may dictate discontinuance of the habit. But a large number of old people have smoked in earlier life though subsequently non-smokers. Personal tolerance to tobacco shows great variations, and there is no doubt that well-marked symptoms may be caused by tobacco. But that moderate smoking diminishes the chance of longevity has certainly not been proved. Much discussion has taken place as to the relation between smoking and arteriosclerosis; it is true that in animals nicotine in considerably larger doses than can be absorbed by smokers, damages the arteries, and Huchard and Lazarus were convinced that it caused arteriosclerosis. Sir Clifford Allbutt,77 after quoting the various opinions, points out that if tobacco be a cause of arterial disease, it acts very slowly, for at 45 years of age, after a quarter of a century’s exposure, the smoker’s arteries are not distinguishable from those of the abstainer’s; and he mentions the arteriosclerosis of the ancient Egyptians and of women as incidents detracting from any argument that tobacco is an important cause of arterial disease.

A large proportion of the centenarians and persons over 80 years of age collected by Sir George Humphry obeyed the adage early to rise and early to bed, and I well remember that he used to lay stress on the factor of getting up directly one woke and so denying the flesh the luxury of further sleep. Whether going to bed early and getting up early is more than an index of a life otherwise spent in accordance with the late Sir Andrew Clark’s “laws of physiological righteousness” may be questioned.

Bodily Conformation.—Long-lived people are usually spare, obesity being rare, and, allowing for some shortening due to age, of a good average height (Humphry). It is interesting in this connexion to quote the conclusions arrived at by Robertson and Ray78 from comparison of groups of long-lived and short-lived white mice in similar conditions. The long-lived were relatively stable, highly resistant to external disturbing factors, displaying subnormal variability and a more or less well-marked, but not invariable, tendency to early overgrowth and relative paucity of tissue accretion in late life; while the short-lived animals showed exactly the opposite features with a tendency to rapid increase of tissue in late life.

The importance of a healthy life with plenty of fresh air, sunshine, exercise, proper diet, and absence of worry hardly needs insistence. Leonard Williams79 has epigrammatically summed up the hygiene of old age as “Fresh air, meagre fare, freedom from care.”