ABSORBENT VESSELS OF BONES. 155 



lion. In early life, this cartilaginous matter pre- 

 ponderates, and the bones are consequently less 

 heavy, more pliable and eiastic, and possessed of 

 greater vitality. In old age, again, the earthy parts 

 predominate, and with them fragility, insensibility, 

 and a lower degree of life. It is from this difference 

 that bones broken in youth reunite in one-third of 

 the time necessary for their reunion in advanced 

 life. 



In some unhealthy states of the system, the pro- 

 portion of earthy matter is greatly diminished, and in 

 some parts it is even altogether removed. The bones 

 become soft, compressible, and incapable of affording 

 protection or support to other parts, to such a degree 

 that instances have occurred in which the lower 

 extremities could be twisted behind, as if made of 

 wire. A slighter degree of the same affection is 

 common in weak, rickety children ; and hence the 

 deformity of limbs so often occurring from absolute 

 insufficiency of the bones to support the weight of 

 the body. 



The practical application to be made of our know- 

 ledge of the constitution of the bones, as parts of 

 our animal frame, and as governed by the ordinary 

 organic laws, will now be obvious. Their health 

 we have seen to depend on the regular supply of 

 nourishment 'by the blood-vessels, on a due supply 

 of nervous energy by the nerves, and on a due 

 balance between the action of the nutrient and ab- 

 sorbent or removing vessels. To the steady obser- 

 vation of these conditions, therefore, we are bound 

 to attend. 



It is a common fault to consider the study of an 

 organ or function complete, when we have viewed 

 it on all sides as an isolated part, without regarding 

 its external relations as constituting an essential 

 portion of its history. Thus, although we examine 

 the structure and functions of the heart, and see 

 that it is a muscle, and that its office is to contract ; 



