4O ELEMENTARY PHYSIOLOGY 



LESSON VI. 

 THE COMPOSITION AND STRUCTURE OF BONE. 



WEIGH a bone of a rabbit, sheep, or other animal, and then put it 

 into a hot and clear fire. Let it remain till it is at a red heat 

 throughout. Now remove it carefully from the fire, let it cool, 

 and weigh again. It will be noticed that the bone has lost 

 about one-third of its original weight, and that what remains is a 

 white and brittle substance. That which has been burnt away by 

 the fire is the organic or animal matter of the bone ; while that 

 which remains is the earthy or mineral substance, sometimes 

 called the ash. From this we learn that bone consists of about 

 thirty-three per cent, of animal matter, and about sixty-seven per 

 cent, of mineral matter. 



The proportion of animal to mineral substance is not the same in all bones. 

 The sternum and the scapula contain a smaller proportion of mineral matter 

 than other bones. The flexible bones of a young child also contain little 

 mineral substance, while the brittle bones of aged persons contain a much 

 larger proportion. 



In the above experiment we completely destroyed the animal 

 matter, and obtained the pure mineral substance or bone ash. 

 By the following experiment we shall be able to dissolve out all 

 the mineral substance, and thus obtain the animal matter : 



Place a bone taken from a recently killed animal in a vessel of weak 

 hydrochloric (muriatic} acid(or\e part of the strong acid to about six of water), 

 and let it remain for a day or two completely covered by the acid. Now 

 pour off the liquid, and cover the bone with fresh acid, setting it aside again 

 for some time. It will be noticed that the bone gradually becomes softer 

 under this treatment, till at last it is flexible and elastic, like a piece of india- 

 rubber. This is due to the gradual removal of the mineral substance it con- 

 tained. This experiment teaches us that the hardness of tone is due to its 

 mineral matter, and that the animal substance resembles cartilage or 

 gristle. 



In this experiment we notice also that the mass of animal 

 matter retains the form of the bone from which it was obtained. 

 In our first experiment, too, we found that the mass of mineral 

 substance was also of the same form as the bone. Hence we 

 conclude that both animal and mineral substances are well 

 blended tog-ether in the bones. 



The animal matter of bone may be converted into gelatine in 

 the following manner : 



Take some bones that have been recently removed from the body of an 

 animal, break them in pieces, and boil them in water for a considerable time. 

 After this pour off the liquid and let it cool. As it does so it will form a 



