BOXE. 



59 



The earthy part may be obtained separate by calcination, by which the 

 animal matter* is completely burned out. The bone will still retain its original 



form, but it will be white and brittle, will 



a b c b a b have lost about one-third of its original 



weight, and will crumble down with the 

 slightest force. The earthy matter confers 

 on bone its hardness and rigidity, and the 

 animal matter its tenacity. 



FIG. - 2&. Section parallel to the surface 

 from the shaft of the femur. Magnified 100 

 times, a. Haversian canals. 6. Lacunae seen 

 from the side. c. Others seen from the sur- 

 face in lamellae which are cut horizontally. 



FIG. 30. Section of bone after the removal of the earthy mat- 

 ter by the action of acids. 



The animal base is often called cartilage, 

 but differs from it in structure, in the fact that 

 it is softer and more flexible, and that when 

 boiled with a high pressure it is almost 

 entirely resolved into gelatin. 



The organic constituent of bone forms about 

 one-third, or 33.3 per cent.; the inorganic 

 matter, two-thirds, or 66. T per cent. ; as is 

 seen in the subjoined analysis of Ber- 

 zelius : 



Organic matter 



Inorganic 



or 

 Earthv matter 



Gelatin and blood-vessels 

 f Phosphate of lime . 

 I Carbonate of lime . 

 "! Fluoride of calcium 

 I Phosphate of magnesia 

 t Soda and chloride of sodium 



33.30 



51.04 



11.30 



2.00 



1.16 



1.20 



100.00 



Some chemists add to this about 1 per cent, of fat. 



Some difference exists in the proportion between the two constituents of bone 

 at different periods of life. In the child the animal matter predominates, whereas 

 in aged people the bones contain a larger proportion of earthy matter, and the 

 animal matter i.s deficient in quantity and quality. Hence in children it is not 

 uncommon to find, after an injury to the bones, that they become bent or only 

 partially broken, whereas in old people the bones are more brittle and fracture 

 takes place more readily. Some of the diseases, also, to which bones are liable 

 mainly depend on the disproportion between the two constituents of bone. Thus 

 in the disease called rickets, so common in the children of the poor, the bones 

 become bent and curved, either from the superincumbent weight of the body, or 

 under the action of certain muscles. This depends upon some defect of nutrition 

 by which bone becomes deprived of its normal proportion of earthy matter, whilst 

 the animal matter is of unhealthy quality. In the vertebrae of a rickety subject 

 Dr. Bostock found in 100 parts 79.75 animal and 20.25 earthy matter. 



Development of Bone. In the foetal skeleton some bones, such as the long 

 bones of the limbs, are cartilaginous ; others, as the cranial bones, are membran- 

 ous. Hence two kinds of ossification are described : the intracartilaginous and 

 the intramembranons ; and to these a third is sometimes added, the subperiosteal ; 

 this, however, is the same as the second, only taking place under different cir- 

 cumstances. 



