424 Gn tke Necessity nf Anhnal Decai/. 



If the animal systeni vvcie so contrived that cverv part might he 

 repaired, why should old age and rigidity supervene ? The idea 

 that the seH&ibility to impression? becomes blunted and jaded by 

 frequent repetitions, is entirely drawn from false analogies. 'Th 

 true, that the ear may become jaded with hearing music, and 

 the eye with seeing colours ; but this is in conseqvier.ce of the 

 alteration which takes place in the state or set of the muscular 

 fibres and nerves belonging to those organs, upon being exercised. 

 It is similar to the limbs becoming weary after long-continued 

 walking or riding. Give the muscles time to rest, and if they 

 have received no permanent injury, no loss but what may be re-r 

 paired,— if their fibres can recover their former set and elonga- 

 tion, the same vividness and freshness of sensation will recur as 

 before. The pleasure-'^ arising from exercise fade as fatigue comes 

 on ; but upon interposing a proper interval, and becoming 

 thoroughly refreshed, the same delight in it is felt as before: 

 nor is it ever found that the exquisiteness and intensity of plea- 

 surable sensations arising from hunting, shooting, music, wine, 

 ^'c, at all diminish upon repetition, so long as the body retains 

 its full vigour ; that is, it is not found that mere repetition has 

 any effect in deadening the sensations. 



The illustration from musical strings giving way as they arc 

 played upon, proves nothing. The set of the particles cf matter 

 in the string alters upon continued tension and vibration ; and 

 the old state cannot be brought back. If it be said that in like 

 manner the set of the muscular fibres, &c. alters and cannot be 

 restored, I agree to the position — that is, I allow that thorough 

 repair does not take place in the animal system. But I ask the 

 cause : I ask whether it would shock our reasoning f.iculties to 

 learn that in some other world there are organized beings, not 

 subject to decay — in whom nutrition and absorption, &c, restore 

 and replace every thing that is lost or disturbed? If it would 

 not, — if we readily acquiesce in the idea, it is incumbent on us, 

 if we would be truly scientific, to endeavour to point out those 

 peculiarities in our system, that preclude the possibility of eter- 

 nal verdure in the individual. 



One of these peculiarities we shall find, I think, in the nature 

 and offices of our vascular system — in the circumstance that the 

 carriers of matter for repair do not carry matter to repair 

 themselves. Without pretending to understand those still dis- 

 puted points concerning the manner of deposition of the coagu- 

 lable lymph, &c. &c. I think I may venture to affirm that our 

 anatomists do not consider the blood in any artery as being the 

 direct and immediate renovator and repairer of the coats of that 

 artery; every artery and every lymphatic, &:c. doivn to tke most 

 ■mmuley being cons-idercd as having their subsidiary artery at- 

 tached 



