18 OUR BODIES AND HOW WE LIVE 



In old age there is more lime in the bones in proportion 

 to the animal matter ; hence they are more brittle and 

 more easily broken than in early life. If broken they unite 

 quite slowly, or not at all. 



Experiment 4. To show the earthy or mineral part of bone. Put 

 a large soup bone on a hot, clear fire until it is at a red heat. At 

 first it becomes black, but after a time it turns white. 



Examine the bone after it is cool. The animal matter has now 

 been burnt out, leaving the earthy or mineral part, a white, brittle 

 substance showing every outline of the bone. 



Experiment 5. To show the animal part 

 of bone. Scrape and clean a chicken's leg 

 bone, part of a sheep's rib, or any other small, 

 slender bone. Add one fourth of a cupful of 

 muriatic acid to a quart of water and place 

 the mixture in a wide-mouthed bottle or glass 

 fruit jar. Soak the bone .in the acid mixture 

 for a few days, adding a little more acid from 

 time to time. 



FIG. ii. The Fibula The mineral matter is slowly dissolved, and 



tied into a Knot t ^ e b one> although retaining its original form, 

 Bftcr Ae Mincr ? 1 becomes so soft as to be readily cut. If the 



experiment be carefully performed, the bone 

 solved by Acid. 



may even be tied into a knot. 



27. General Structure of the Bones. Take a long bone, 

 like that from a sheep's leg or even a part of a beef shin 

 bone, and saw it lengthwise. Note that the ends are soft 

 and spongy, while the shaft is hard and compact. The 

 central cavity runs almost the whole length of the bone. 

 It is filled, in life, with a soft, fatty substance called marrow. 



If the bones were solid, they would be much too heavy 

 for ordinary use. A bone may be hard as a rock on the 

 outside, on account of its thin, dense layer of compact 

 bony tissue, and yet be light because of its cavity and the 

 trellis work of loose, spongy texture at the ends. 



