CHAPTER VI. 

 ON OLD AGE AND DEATH. 



700. After an animal has attained its growth, and all its 

 natural transformations being completed, it has remained for a 

 period in its state of full development, everything in its nature 

 tends to decline. Its fluid elements are used up, and become 

 more inspissated and earthy ; its solid constituents are partly 

 destroyed, partly rendered harder and denser; its canals are 

 filled up and ossified. All this occurs from natural causes 

 existing throughout the organism, and for the most part in 

 virtue of physical and mechanical forces. The consideration 

 of these belongs to the physiology of mechanical nature; we 

 have only to discuss the decay of the proper animal forces. 



701. In old age, the brain and nerves appear to dry up, and 

 become flaccid ; the nerves even of the organs of sense become 

 hebete from constant use and the growth of impediments to 

 their functions, so that external impressions are less felt, and 

 external sensations are less readily excited. Hence the dimi- 

 nished activity of the sexual instincts and desires, the diminished 

 muscular energy, the insensibility and dullness of age. Internal 

 impressions following the same rule as external, the mental 

 powers become enfeebled, the memory fails, the judgment is 

 impaired and becomes slow and undecided. Hence the appear- 

 ance of greater wisdom and prudence than the old really 

 possess, &c. 



702. Since every kind of animal force decays, whether 

 manifested in the insentient, the merely sensational, or the 

 reasoning animal, destruction naturally impends over aU animals, 

 and every animal is naturally mortal. The natural necessity 

 of this interruption of animal life is not only shown by the 

 laws of the economy, but also by the operation of remote phy- 

 sical and mechanical causes, which partly destroy — insensibly 

 and gradually — the structure of the animal machines, partly inter- 

 rupt the natural action of their forces, as well in themselves as 

 in the mechanical machines, in a way not known. The subject 

 belongs, however, to the physiology of the mechanism of animal 

 bodies (Haller's 'Physiology,' § 31). 



