CHAP. V.] BONE. 99 



abundant, as well as perhaps defective in quality, are more brittle 

 than young ones, and old persons are more liable to fractures. 

 But in the young, in whom the organic processes are active, and 

 whose animal matter is fully adequate in quantity and quality to 

 the wants of the system, the bones possess their due degree of 

 flexibility, and hence in them fractures are less frequent ; the co- 

 hesive force of the bones being sometimes so considerable, that they 

 will bend to a great degree before yielding. 



The following table from Schreger illustrates the relative pro- 

 portions of the two constituents, at three periods of life, in 100 

 parts of bone : 



Child. Adult. Old. 



Animal matter . . 47'20 . 20-18 . 12-2 

 Earthy matter . . 4848 . 74'84 . 84'1 



or it may be stated in general terms, that in the child the earthy 

 matter forms nearly one half the weight of the bone, in the adult 

 it is equal to four fifths, and in the old subject to seven eighths; a 

 conclusion agreeing in the main with that drawn from the analyses 

 of Davy, Bostock, Hatchett, and others. 



It had long been known that certain bones of the body contained 

 these constituents in other proportions than those named; for ex- 

 ample, the petrous portion of the temporal bone had been shewn by 

 Davy to owe its stony hardness to a large proportion of earthy mat- 

 ter. But Dr. G. O. Rees has lately pointed out some interesting 

 particulars as to the relative proportions of these elements in the 

 composition of different bones. 



The long bones of the extremities have, according to Dr. Rees' 

 analysis, more earthy matter than the bones of the trunk. The 

 bones of the upper extremity have a larger proportion of the same 

 material than those of the corresponding bones in the lower; the 

 humerus has more than the radius and ulna; the femur more than 

 the tibia and fibula ; while the bones of the fore-arm, as well as 

 those of the leg, are respectively alike in constitution. The ver- 

 tebrae, ribs, and clavicles are similarly constituted. The ilium has 

 more earthy matter than the scapula or sternum; the bones of the 

 head have more of this material than those of the trunk. 



In the foetus the same law prevails as regards the relative quan- 

 tity of the earthy matter, excepting that the long bones, and the 

 cranial bones, do not contain the excess of earthy matter which 

 characterizes them in the adult. 



The diseased state, called Rickets, so common in the children of 

 scrofulous parents, and in the ill-nourished ones of the lower orders, 



H2 



