24 Additional Notes. 



They are also occasionally influenced by sensation, as is seen in the 

 paleness occasioned by fear, or the blush of shame and anger; and lastly 

 the motions of the heart are sometimes assisted by volition; thus in those 

 who are much weakened by fevers, the pulse is liable to stop during 

 their sleep, and to induce great distress; which is owing at that time 

 to the total suspension of voluntary power; the same occurs during 

 sleep in some asthmatic patients. 



2. The debility of approaching age appears to be induced 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 asso- 

 ciation 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 vasorum, or 

 capillary arteries of the coats of the other arteries. 



The veins of elderly people become turgid or distended with blood, 

 and stand 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 frequently, to receive, as fast as usual, the 

 returning blood ; and their apparent prominence on the skin is occa- 

 sioned by the deficient secretion of fat or mucus in the cellular mem- 

 brane; and also to the contraction and coalescence and consequent less 

 bulk, of many capillary arteries. 



3. Not only the muscular fibres lose their degree of excitability 

 from age, as in the above examples ; and as may be observed in the tre- 

 mulous 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 stimulus of the sensorial power 

 ofsensation alsoless affects the aged, who grieve less for the loss of friends 

 or for other disappointments; it should nevertheless be observed, that 



