Though much more exact knowledge is needed, it appears that the average age attained in different races and countries varies, probably in the main as the result of environmental influences. Thus temperate or moderately cold climates are more conducive than tropical countries, such as India, to the slow development of maturity and so to a longer life. The Balkans, Greece, Scandi navia, the Pyrenees, California, and small islands have been regarded as favourable to longevity ; a high elevation and length of days have also been correlated, but Swiss statistics do not bear this out, and in the case of the monks of Mount Athos—an out standing example—and elsewhere simplicity of life may have played a part. The low infantile mortality and remarkable longevity of the Jews have been ascribed to their obedience to the Mosaic laws of health, or alternatively to a hereditary trait, developed as a result of the survival of the fittest after long persecutions and hardships, but this inborn influence has been disputed by Fishberg who supports the view that their habitual care for their children is the real factor. Savage races do not encourage survival of the ageing, whereas civilized nations pro tect and provide for them. Females are more long-lived than males in every decade after the first, and among centenarians women outnumber men in the proportion of three to one. Graham Bell's analysis of the Hyde genealogy, dealing with 8,792 persons and dating from the I7th century, shows that the proportion of those living long increased with the size of the family up to families containing nine and ten children, and then fell in the case of larger families; that the first-born lived as long as subse quent children; and that children born between four and eight years after their parents' marriage were on the average longer lived than those born earlier or later.
Inborn vitality may counteract the evil influences of unhealthy environment and bad habits, such as overcrowding in towns and alcoholism, and so explain the occasional longevity of those who have lived in most unfavourable circumstances; for example, the contrast between two aged brothers, one a confirmed toper, the other a total abstainer. Of the hereditary factors innate vitality of the nervous and the circulatory systems are the most im portant; the nervous system decides the mental disposition and the reactions of the body as a whole. Cazalis' aphorism "Man is as old as his arteries" expresses the advantage of possessing a circulatory system which does not degenerate readily, harden into the condition of arteriosclerosis, or show an excessive blood pressure; for it is well known that the members of some families tend to die about the age of 6o from apoplexy, heart or kidney disease, the latter being often the result of arterial disease in the kidneys.
character, in the individual, whereby the cells of the body are damaged so that they tend to degenerate and become old pre maturely, must be given due weight it has been stated that only those who have escaped illness up to the age of 6o years are likely to reach extreme old age, but nearly half of the persons between the ages 8o and zoo, analysed by Sir George Humphry, had passed through a severe illness, in many of them an acute infection. An acute illness may be the apparent starting point of old age and senescence, especially if sufficient time for convalescence is not allowed. It has been suggested that the deteriorating influence of malaria on individuals may, by its mass effect, account, in some degree at any rate, for the decadence of Magna Graecia (W. H. S. Jones). Functional activity, mental and bodily, plays an important part in postponing the advent of morbid old age, and there is more danger of rusting out than of wearing out, provided the body is healthy and the mind free from worry. The advanced ages of many dignitaries of the Church and the bench and of prime ministers, though many of these may be supermen, point to the beneficial influence of long continued activity. Among painters Giovanni Bellini, Michael angelo, and Sidney Cooper worked up to nearly their death, and Titian was painting with "incomparable steadiness of hand" when cut off by the plague at the age of 99. The same retention of productivity was seen in Voltaire, Lithe, Anatole France, Goethe, von Ranke, and Frederick Harrison. The members of the Academie Francais are long-lived, and thus doubly justify their title of "the immortals." Retirement, often looked forward to in early life, is a source of danger, as it may bring with it cessa tion from activity.
The majority of centenarians have been small eaters, and several aphorisms point to the evil, if slow, effect of being a good trencherman, such as Montaigne's "Man does not die, he kills himself" and the forcible proverb "You dig your grave with your teeth." Overfeeding by overworking the resources of the body leads to metabolic disease, such as diabetes mellitus, and to arterial, heart and kidney affections, which are preceded often by long periods of latency during which the individual flatters him self on his vigour, but in which his arterial blood pressure is unduly high. Poverty, within limits, is an advantage inasmuch as it removes the dangers of excessive eating, particularly of meat, after the body has reached maturity. The beneficial effects of a meagre dietary were set forth by the noble Venetian Luigi Cornaro (1467-1566), by Metchnikoff, Henry Thompson the surgeon, Hermann Weber, and many others who practised their own precepts. With regard to the influence of alcohol there can be no doubt, as the actuarial reports of life assurance companies amply prove, that excess is harmful. It is true that Raymond Pearl's statistical enquiry into over 5,000 lives at Baltimore showed that "a moderate use of alcohol does not tend to shorten life." But what constitutes moderation is open to criticism.