98 LOCOMOTION. [CHAP. v. 



of support, or levers for motion, or it encloses cavities, affording 

 protection to soft arid vital organs. 



To a superficial examination bone presents the following proper- 

 ties : hardness, density, a whitish colour, opacity. An examination 

 of its physical constitution will explain these characters. 



Bone contains less water than any other organ in the body; and 

 exposure to air, even for a short time, removes the fluid by evapora- 

 tion: to this, in part, may be attributed its hardness. Bone consists 

 of an inorganic and an organic material, which may be obtained 

 separately by very simple processes. Steep a bone in dilute mineral 

 acid, muriatic or nitric ; the earthy matter is dissolved out by the 

 acid, and the organic substance remains, retaining the original shape 

 and size of the bone. In fact, we obtain, by this process, the car- 

 tilaginous nidus of the bone, upon which its form depends. The 

 vessels of the bone ramify throughout this mass ; for if they have 

 been injected previously to the action of the acid, they will be dis- 

 tinctly seen ramifying through the semi-transparent animal sub- 

 stance. A preparation of this kind dried, and afterwards preserved 

 in spirits of turpentine, serves beautifully to exhibit the disposition 

 of the vessels in bone. 



By subjecting a bone to a strong heat in a crucible, the animal 

 part will be burnt out, and the earthy part will remain. Still the 

 bone retains its form, but the cohesion between the earthy particles 

 is extremely slight, so that the least touch will destroy its con- 

 tinuity ; a fact which obviously points to the animal matter as 

 affording to bone its strength of cohesion. 



Bone may be deprived of its animal matter by long- continued 

 boiling, under strong pressure, in a Papin's digester. The animal 

 matter is extracted, in combination with water, in the form of gela- 

 tine ; and the weight of the quantity which may thus be obtained 

 will, owing to this union with water, exceed by three or four times 

 that of the bone itself. 



A certain proportion between these two constituents of bone is 

 necessary to the due maintenance of its physical properties. To the 

 earthy part it owes its hardness, its density, its little flexibility : 

 but it is equally necessary for these properties that the animal por- 

 tion shall be healthy, and in proper quantity; for the cohesion of 

 the particles of the former is secured entirely by it. A due pro- 

 portion of the animal part gives bone a certain degree of elasticity; 

 and, were it not for the earthy matter, bones w r ould be exceedingly 

 flexible, as may be shewn in a bone deprived of its calcareous mat- 

 ter by acid. Hence old bones, in which the animal matter is less 



