434 DECLINE OF THE SYSTEM. 



consolidation, begun from the earliest period of development, 

 is still advancing, and is producing in the fluids greater thick- 

 ness, and a reduction of their total quantity; and in the so- 

 lids, a diminution in the proportion of gelatin, and the con- 

 version of this element into albumen. Hence, all the tex- 

 tures acquire increasing solidity, the cellular substance 

 becomes firmer and more condensed, and the solid structures 

 more rigid and inelastic: hence, the tendons and ligamentous 

 fibres growing less flexible, the joints lose their suppleness, 

 and the contractile power being also impaired, the muscles 

 act more tardily as well as more feebly, and the limbs no 

 longer retain the elastic spring of youth. The bones them- 

 selves grow harder and more brittle; and the cartilages, the 

 tendons, the serous membranes, and the coats of the blood 

 vessels, acquire incrustations of ossific matter, which inter- 

 fere with their uses. Thus are all the progressive modifica- 

 tions of structure tending, slowly but inevitably, to disqua- 

 lify the organs for the due performance of their functions. 



Among the most important of the internal changes con- 

 sequent on the progress of age are those which take place in 

 the vascular system. A large proportion of the numerous 

 arteries, which were in full activity during the building of 

 the fabric, being now no longer wanted, are thrown, as it 

 were, out of employment; they, in consequence, contract, 

 and becoming impervious, gradually disappear. The parts 

 of the body, no longer yielding to the power applied to ex- 

 tend them, oppose a gradually increasing resistance to the 

 propelling force of the heart: while, at the same time, this 

 force, in common with all the others, is slowly diminishing. 

 Thus do the vital powers become less equal to the demands 

 made upon them; the waste of the body exceeds the supply, 



other hand, we were to regard each separate shoot as an individual organic 

 body, and every layer as constituting 1 a distinct generation of shoots, the 

 older being covered and enclosed in succession by the younger, the great 

 longevity of a tree would, on this hypothesis, indicate only the permanence 

 of the species, not the indefinitely protracted duration of the individual plant. 



