Old Age and Death. 25 



when the sensorial power of irritation is much exhausted, or its produc- 

 tion muchdiminished ; the sensorial power of sensation appears for a time 

 to be increased ; as in intoxication there exists a kind of delirium and 

 quick flow of ideas, and yet the person becomes so weak as to totter as he 

 walks; but this delirium is owing to the defect of voluntary power to 

 correct the streams of ideas by intuitive analogy, as in dreams : see 

 Zoonomia: and thus also those who are enfeebled by habits of much 

 vinous potation, or even by age alone, are liable to weep at shaking 

 hands with a friend, whom they have not lately seen; which is owing 

 to defect of voluntary power to correct their trains of ideas caused by 

 sensation, and not to the increased quantity of sensation, as I formerly- 

 supposed. 



The 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 are 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 of 

 the other words of a language, which are more frequently repeated. 



4. This disobedience of the fibres of age to their usual stimuli, has 

 generally been ascribed to repetition or habit, as those who live near 

 a large clock, 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 



