The basis of the physiology of old age is progressive diminution in functional activity, which corresponds to the characteristic structural atrophy of the organs and tissues. Thus the lowered functional activity of its glands is manifest in the dry skin; according to Haneborg176 there is usually a fall in the percentage of hydrochloric acid in the gastric juice, though Bell177 disputes this. The lessened amount of mucus from the intestine probably plays some part in the tendency to constipation. Other evidences of lowered metabolic rate are seen in the diminished efficiency of the acid-base equilibrium (MacNider178) and the increased degree of urea-nitrogen in the blood, as shown in 50 per cent of 41 persons between 70 and 88 years of age examined by Rappleye.179 Temperature.—Before the era of the clinical thermometer it was supposed that the body temperature of the aged was below normal. This belief was part of the ancient view that the cause of old age was exhaustion by the natural heat of the radical moisture which, like lamp oil, supported the innate heat and with the passage of years could not be supplied as perfectly as before; as a result of this loss of radical moisture the body was thought gradually to dry and cool.180 But it is now known that the internal temperature is almost constant at all ages, and Charcot proved that the only real difference is that the axillary is lower than the rectal reading; this is due to the diminished vascularity of the skin and to the corresponding fall in the loss of heat, which again may be correlated with the lower metabolic rate of old age. Aub and Dubois’181 observations on six men between 77 and 83 years of age, mainly with arteriosclerosis, granular kidney, and emphysema, showed that the basal metabolism was 12 per cent below the average for men between 20 and 50.

Blunting of sensibility to pain is a beneficent process, suggesting that with the gradual process of involution and approach to a physiological death the need for the warning normally conveyed by symptoms is no longer needed. This is connected with the simultaneous atrophy of the nervous tissues which look after the conduction, perception, and reference of pain. The latency of disease, as shown by an absence of the characteristic symptoms observed in earlier adult life, is often remarkable in the aged. Thus death may occur suddenly from extensive but entirely unsuspected pneumonia; the passage of biliary or urinary calculi may be unaccompanied by the violent colic of these events in ordinary cases, and extensive malignant disease may exist without any definite localizing discomfort. This failure in the power to react is also shown in fevers and infections (vide p. 142).

Cutaneous sensation is little affected, and indeed the aged are very sensitive to cold. Taste and smell are impaired, and presbyopia is due to changes in the crystalline lens. The pupils are contracted and the iris sluggish. From weakness of the orbicularis palpebrarum muscle ectropion and epiphora may noticeably change the facial appearance. With advancing years hearing commonly becomes less acute from various causes, and after 60 there is a successive decrease in the number of persons with normal hearing. According to Albert Gray182 there is probably a characteristic form of deafness for the higher notes of Galton’s whistle in all old people, even when for all practical purposes there is no obvious defect or tinnitus; this he regards as due to progressive atrophy of the ligamentum spirale. Chronic progressive labyrinthine deafness, due to atrophy of the auditory nerve and fibrosis of the ductus cochleariae, is the most common condition in persons over 60. Fixation of the stapes frequently causes deafness, and the sequels of middle-ear disease accumulate with advancing years. Gouty eczema of the external auditory meatus and collections of wax may seriously interfere with hearing. Tinnitus in the elderly is commonly associated with high blood pressure and arteriosclerosis.

Appetite for food is sometimes capricious; old people may eat excessively, possibly because the pleasures of the table are the only ones to which they feel equal. Muscular movement is slow and somewhat uncertain, and the reflexes are diminished except in the presence of sclerosis of the spinal cord. According to Moebius the knee-jerk is often absent in normal old persons, but Sternberg, by employing methods of reinforcement not available in Moebius’ time, found that it was invariably present even in the tenth decade.

The sleep of the aged is less continuous, and from interruptions often appears to them to be much less than it really is. There is often a tendency to irregularity, bad and good nights alternating. But too much attention to disturbed sleep in the aged must be avoided, as hypnotics are inadvisable, and it has been urged by Sir Hermann Weber and others that too much sleep is more harmful than too little.

In old age the mental condition varies in different individuals according to their previous character and their present physical state. Freedom from sexual and other perturbations often renders the minds of old people calm, tolerant, less susceptible to disappointed ambition, and philosophic when the part of spectator has been accepted in place of that of actor in life’s drama. In what may be regarded as normal old age psychical activity diminishes; not only do initiative, elasticity, and originality fail, but new ideas and fresh lines of thought are assimilated with difficulty; hence the old are commonly conservative and laudatores temporis acti. Mental fatigue occurs more readily and the power of concentration and attention is impaired so that the old may appear deaf; the mind begins to show disintegration and a return to the primitive condition in which each act demands individual care; it has indeed been said that old age is nothing but progressive fatigue. A less agile memory for names is commonly one of the early symptoms of senescence, and long precedes the characteristic loss of memory for recent events while that for the remote past remains, as if the nerve cells were photographic plates which in course of time have all become occupied with impressions. With commencing failure of memory there is often a tendency to make the same remark or tell the same story repeatedly, to mislay things, and unconsciously to become careless about personal appearance and habits. As a kind of protest against the inevitable there may, in the early stage of old age, be a tendency to ape the young and to conceal the true age; thus a man may remove the date of his birth from Who’s Who and books of reference, and a mother may delay the “coming-out” of her daughter. On the other hand, at a later stage there may be the opposite desire to appear a wonderful prodigy of senescence. The old are notoriously less subject to feel the loss of relatives and friends by death; they become more self-centred; this may be because retirement from active work switches their minds on to their own feelings, and possibly in part depends on loss of touch with the external world, resulting from failure of the sense organs. This when exaggerated develops into selfish dependence and demands on relatives. Senile vanity is not uncommon, and Eden Phillpotts183 remarks that all old people love to be in the centre of the stage, one of the pathetic things in life being that they are seldom allowed to be there. The ego-centric frame of mind may lead to hypochondriasis with fads and meticulous attention to details of personal health and to experiments in diet and patent medicines. Loss of control, due to failure of the higher centres, engenders restlessness, garrulity, emotional weakness, and peevishness. There may be considerable variation in the moods, so that the deep depression of one day may vanish the next, and irritability and apathy may alternate. Regression, which closely corresponds to the “devolution” of Hughlings Jackson, who argued that in disease the organism tends to retrace the steps of its development, accounts for the phenomena of “the second childhood.” Thus the old are prone to nervous apprehension, and liable to suggestion and to hysteria which Rivers184 defined as a protective mechanism representing a recrudescence of the reaction to danger in an early stage of animal development. Will power, like their gait, becomes hesitant and uncertain. This devolutionary change progresses partially and not universally; memory for personal names, as mentioned above, is often the first to fail, because, like the mathematical faculty, it has from the attendant difficulty a high place in the order of mental processes; hence forgetfulness of personal names is a criterion of psychical fatigue and neurasthenia (Dupuis185).

In old animals it is natural for the instinct of self-preservation to fade, as is exemplified in the day-flies which in their larval stage are well endowed with this property, and as their end draws near animals seem to acquire an instinct for death comparable to that for sleep. But in human beings, although they usually dislike old age, there is generally what Matthew Arnold186 called “a passionate, absorbing, almost bloodthirsty clinging to life.” Metchnikoff specially investigated this point and found hardly any instances in which death was anticipated with the same feelings of pleasure as is sleep by the weary. Considering the discomforts of many old people it is rather remarkable how very seldom they endorse the words of the burial service: “We give thee hearty thanks for that it hath pleased thee to deliver this our brother out of the miseries of this sinful world.” Various explanations have been offered for this want of harmony between the mental and physical states of the old; it has been ascribed to the idea of eternal punishment, and to the presence of pathological conditions which bring on senility and death prematurely and thus alter what should be the normal mental attitude of healthy old age. In speaking of the usual fear of death in old people it should be mentioned that shortly before death this commonly disappears and, as G.E. Day,187 R.W. Mackenna,188 and Thompson and Todd point out, the aged when seriously ill commonly regard death as a welcome release; the famous William Hunter’s last words in his sixty-fifth year expressed his sense of resignation: “If I had strength enough to hold a pen, I would write how easy and pleasant a thing it is to die.”

The Cardio-Vascular System.—The pulse rate is usually rather increased in frequency as compared with that in adult life; extra-systoles are so common in persons who appear otherwise normal that they cannot be regarded as having any important significance. Among Sir George Humphry’s collection of 824 persons over 80 years of age one-fifth had an irregular or intermittent pulse.

Although, like arteriosclerosis, a well-marked high blood pressure without evidence of renal disease, to which Sir Clifford Allbutt has given the name of senile plethora or hyperpiesia, is common in the decline of life, it is a pathological and not a physiological change; and a distinction must be drawn between the gradually rising blood pressure seen from birth onwards and an increase above that normal to an arterio-vascular system that has been active for over half a century. In the same way the venous pressure increases with age (Hooker189). That a definitely high blood pressure in the aged is pathological appears to be shown by observations quoted by Councilman from the Peter Bent Brigham Hospital, Boston; among 94 patients (male and female) averaging 66 years of age, 44 per cent with cardiac hypertrophy as shown by necropsy, had an average blood pressure of 158systolic / 88diastolic, whereas the 56 per cent without cardiac hypertrophy had an average blood pressure of 130/78. In both series the differences between males and females were never more than 7 mm. Hg. From observation of 102 Chelsea pensioners over 75 years of age Thompson and Todd found that the average blood pressure was 145systolic / 80diastolic, estimations varying from 190/100 to 115/70, and that the average pulse pressure, or difference between the systolic and diastolic pressures, was 67 mm. They came to the conclusion that it was not possible to arrive at a normal blood pressure for old people on account of the varying conditions of the heart and arteries.190 The urine, in consequence of the lowered metabolism and general atrophy, is somewhat diminished in quantity with a fall in the solids, though the specific gravity remains about normal. The chlorides are stated to be normal and the phosphates and urea to be diminished. Slight glycosuria as a result of a low sugar tolerance (vide Spence191) is not uncommon, especially in obesity. Prolonged confinement to bed has been thought to be responsible for casts in the urine. A trace of albumin is not rare; this may be due to various factors, and in itself is not a cause for anxiety; but a well-marked fall in the specific gravity is a sign of renal inadequacy which may be preceded and anticipated by the discovery of nitrogen retention in the blood.

Sexual activity in man wanes generally speaking after 50, but there are great variations in this respect, and sometimes there are periods of considerable excitement in old men, often thought to be associated with prostatic enlargement.

It would naturally be expected that wounds and fractures of bones would heal more slowly in the old than in the young, and, according to Carrel and Ebeling,192 the cicatrization of human wounds varies inversely, if accurately measured, with the age of the patient; Humphry, however, found that, provided sloughing did not occur, wounds and ulcers in the aged heal as quickly as in middle life, and that the failure of union in intracapsular fracture of the neck of the femur is due to want of apposition and not to the age of the patient.

In some respects the reaction to drugs in the senescent body is different from that in ordinary adult life. In old people absorption from the alimentary canal is slow and this is particularly so with gelatin-coated pills and drugs, such as cinchona, containing tannin, which should therefore be avoided. The physiological response to drugs is slower and more prolonged than in early life, so that for this reason and from the frequency of constipation an accumulated action is thought to be more likely to occur in the aged. It is sometimes said that large doses are not borne well by the old and that morphine is dangerous as it is in infants, but Nascher193 states that if, in order to obviate the paralysing effect of morphine on a weakened respiratory centre, atropine is given before the morphine so that their action can be timed to coincide, instead of giving them at the same time when the effect of the atropine comes later, morphine can be given in the same doses as in maturity. Purgatives may be required in larger doses than in ordinary practice. According to Leonard Williams194 bromides are likely to produce mental confusion in old people and if persisted in, even in ordinary doses, may be followed by vascular thrombosis and permanent impairment of the intellectual powers. Sedatives and hypnotics when necessary should be given in small doses and discontinued as soon as possible; but they may be necessary for restlessness which would otherwise seriously exhaust the failing strength.