OCR Text |
Show Additional Notes. They are also occasionally influenced by sensation, as is seen in the paleness occasioned by fear, or th~ blush o.f shame an~ ~nger; an.d lastly tl otions of the heart are sometunes assisted by volltwn; thus m those wlheo m a re much weakened by fevers, the pulse I·S 11· a bl e to stop d un·n g their sleep, and to induce great distress; which is owing at that ti.me to the total suspension of voluntary power; the same occurs dunng sleep in some asthmatic patients. . 2. The debility of approaching age appears to be mduced by the inactivity of many parts of the system, or their disobedience to their usual kinds and quantities of stimulus; thus the pallid appearance of the skin of old age is owing to the inactivity of the heart, which ceases to obey the irritation caused by the stimulus of the blood, or its association with other moving organs with its former energy; whence the capillary arteries are not sufficiently distended in their diastole, and consequently contract by their elasticity, so as to close the canal, and their sides gradually coalesce. Of these, those which are most distant from the heart, and of the smallest diameters, will soonest close, and become impervious; hence the hard pulse of aged patients is occasioned by the coalescence of the sides of the vasa vasonm , or capillary arteries of the coats of the otlier arteries. The veins of elderly people become turgid or distended with blood, and stat~d prominent on the skin; for as these do not possess the elasticity of the arteries, they become distended with accumulation of blood; when the heart by its lessened excitability does not contract sufficiently forcibly, or frequent1y, to receive, as fast as usual, the rettlrning blood; and their apparent prominence on the skin is occasioned by the deficient secretion of fat or mucus in the cellular membrane;. and also to the contraction and coalescence and consequent less bulk, of many capillary arteries. 3. Not only the muscular fibres los·e their qegree of excitability . from age, as in the above examples; and as may be observed in the tremulous hands and feeble step of elderly persons; but the organs of sense become less excitable by the stimulus of external objects; whence the sight and hearing become defective; the sti1pulus of the sensorial power of sensation also less affects the aged, who grieve less for th elossoffriends or for other disappointments; it should nevertheless be observed, that Old Age and Death. ':hen the se.ns~r~al power of irritation is much exhausted, or its productiOn m.u ch dummshe~; ~he s~nso~ial power of sensation appe~rs for a time to be Increased; as m mtoxrcatwn there exists a kind of delirium and quick flow of ideas, and yet the person becomes so weak as to totter ashe . walks; but this deliriun: is owing to the defect of voluntary power to correct ~he streams of 1deas by intuitive analogy, as in dreams: see Zoonomm: and thus also those who are enfeebled by habits of much vinous p.otatiou: or even by age alone, are liable to weep at shaking hands w1th a fl'lend, whom they have not lately seen; which is owing to defect of voluntary power to correct their trains of ideas caused b . 1 1 . y sensatron, an< not to t 1e mcreased quantity of sensation, as I formerly supposed. ThG same want of voluntary power to keep the trains of sensitive ideas consistent, and to compare them by intuitive analogy with the order of nature, is the occasion of the starting at the clapping to of a door, or the fall of a key, which occasions violent surprise with fear and sometimes convulsions, in very feeble hysterical patients, and is not owing I believe (as I formerly supposed) to increased sensation; as they arc less sensible to small stimuli than when in health. Old people are less able also to perform the voluntary exertions of exercise or of reasoning, and lastly the association of their ideas becomes more .imperfect, as they are forgetful of the names of persons and places; the associations of which are less permanent, than those oi the other words of a language, which are more frequently repeated. 4. This d isobeclience of the fibres of age to their usual stimuli, has generally been ascribed to repetition or habit, as those who live near a large dock, or a mill, or a waterfall, soon cease to attend to the perpetual noise of it in the day, and sleep during the night undisturbed. Thus all medicines, if repeated too frequently, gradually lose their effect; as wine and opium cease to intoxicate: some disagreeable tastes, as tobacco, by frequent repetition cease to be disagreeable; grief and pain gradually diminish, and at length cease altogether; and hence life itself becomes tolerable. This diminished power of contraction of the fibres of the muscles .or organs of sense, which constitutes permanent debility or old age, may arise from a deficient secretion of sensorial power in the brain, as E |