18 THE FRAMEWORK OF THE BODY 



2. The more delicate the organ, the more completely does 

 Nature shield it. For example : the brain, which is soft in 

 structure, is enclosed on all sides by a spherical box of bone ; 

 the eye, though it must be near the surface of the body to 

 command an extensive view, is sheltered from injury within 

 a deep recess of bone ; the lungs, requiring freedom of motion 

 as well as protection, are surrounded by a large "chest" of 

 bone and muscle. The bones serve other useful purposes. They 

 give permanence of form to the body, by holding the softer 

 parts in their proper places. They assist in movement, by 

 affording points of attachment to those organs which have 

 power of motion the muscles. 



3. The Form and Composition of the Bones. The shape and 

 size of the bones vary greatly in different parts of the body, 

 but generally they are arranged in pairs, one for each side of 

 the body. They are composed of both mineral and animal 

 substances, united in the proportion of two parts of the former 

 to one of the latter; and we may separate each of these sub- 

 stances from the other for examination. First, if we expose a 

 bone to the action of fire, the animal substance is driven off, or 

 " burned out." We now find that, though the shape of the 

 bone is perfectly retained, what is left is no longer tough, and 

 does not sustain weight as before. Again, we may remove the 

 mineral portion, which is a form of lime, by placing a bone in 

 a dilute acid. The lime will be dissolved out, and the shape 

 of the bone remain as before; but now its firmness has dis- 

 appeared, and it may be bent without breaking. (Read Note 2.) 



4. If, for any reason, either of these ingredients is dispro- 

 portionate in the bone during life, the body is in danger. The 

 mineral substance is useful in giving rigidity of form, while 



2. Experiment. To demonstrate the presence of the mineral mat- 

 ter in bone, obtain a sheep's rib, clean it thoroughly and macerate it 

 for three or four days in dilute muriatic acid (one part acid to eight of 



2. The more delicate the organ ? Example in relation to the brain ? The eye ? The 

 lungs ? The services performed by the bones ? 



3. Their shape and size ? Of what composed ? Possibility of being separated ? Effect 

 of fire ? Of dilute acid ? 



4. Effect of deficiency of ingredient ? Usefulness of the lime ? Of the animal sub- 

 stance ? Effect of their union ? Condition, in youth ? Old age ? 



