LONGEVITY. 341 



dency is to increased action. The growth of the body 

 depends on this. The functions being all in an active 

 state, a large quantity of blood is formed, from which 

 the materials are supplied that increase the body and 

 make up for the daily waste going on. This addition 

 of new matter and the force of the circulation distend 

 the different parts and add to their bulk. The 

 addition of new matter, after some time, and the 

 degree to which the extension has been carried 

 impede the further continuance of the process, and 

 the power of the arteries becomes so balanced with 

 reference to the condition of the system as to cause 

 its present state to continue. The balance, however, 

 is soon destroyed by the diminished action ; and the 

 veins being more easily distended than the arteries, 

 and having experienced less alteration in their tex- 

 ture, while they also partake less of vital action, the 

 blood is more disposed to accumulate in them*. 



This principle may be made still more plain by 

 saying, that as age advances the fine hair-like blood- 

 vessels, which branch off in every direction through 

 the body, and more particularly through the skin and 

 near the surface, become obstructed and imperforate, 

 and consequently the skin and the other parts to 

 which they run, not being supplied with their nou- 

 rishment of fresh blood, shrink and wither ; the 

 internal parts becoming gradually more stiff and hard, 

 and the skin first sallow and then dry and wrinkled. 

 In such cases, when the smaller blood-vessels are 

 obliterated, the larger ones swell with blood which 

 cannot get vent, and this is the reason why we see 

 old people's veins swell, as on the back part of the 

 hands or feet. 



Insects, though they have no circulating blood 

 like the larger animals, furnish an analogical corro- 



* Cullen's Physiology, p. 249. 



