INCREASE AND DIMINUTION OF BONES. 153 



had the scull been incapable of undergoing change, 

 death would have to a certainty ensued. The scull 

 owes this power of adaptation entirely to its pos- 

 sessing vessels and nerves, and to its undergoing a 

 constant decay and renewal, like the other parts of 

 the system. 



The same phenomena are exhibited by the bones 

 of the chest. When tumours arise, or collections 

 of fluid take place within that cavity, there is a 

 constant effort on the part of nature to take advan- 

 tage of this constitution of the bones, and to cause 

 them so to expand, as to save the lungs and heart 

 from hurtful pressure, and allow respiration and 

 circulation to go on unimpaired. 



In the opposite circumstances of diminished vol- 

 ume of the soft contents of the cavities, the same 

 law enables the bone to decrease in a correspond- 

 ing proportion, and consequently to continue the 

 protection which it affords to its contained organs. 

 Thus, were the bone to remain unaltered, when, in 

 cases of disease and in old age, the brain diminishes 

 in size, the cavity of the scull would be only 

 partially filled, and the brain, so far from being pro- 

 tected, would be jolted backwards and forwards, up- 

 wards and downwards by every motion of the head 

 or body, till its structure should be utterly destroyed, 

 and life itself extinguished. 



To those who are unacquainted with the laws of 

 nutrition of organized bodies, and who are accus- 

 tomed to notice the hard and unyielding nature of 

 bone, without having any adequate perception of 

 the particular uses of the adaptation of the hard 

 to the soft parts, this adaptation may seem strange 

 and improbable ; but a little consideration will satisfy 

 every one that it could not have been otherwise. 



In infancy, when the lungs are imperfectly devel- 

 oped, the chest is narrow, flat, and confined, and the 

 ribs almost in close juxtaposition. In youth and 

 in middle age, when force and activity require ful- 



