178 STUDIES IN PHYSIOLOGY 



75). The living tissue and the fatty marrow are easily 

 removed by placing the bone in a hot fire. As the bone 

 burns, it gives off the familiar smell that is characteristic of 

 proteid, and a black color appears, which demonstrates the 

 presence of carbon. If the flame is hot enough, the carbon 

 is oxidized, and a white, brittle substance is left, which 

 preserves perfectly the form of the bone. The marrow 

 cavity is, however, completely empty, and in the burned 

 bone the porous character of the spongy tissue becomes 

 more evident. 



By weighing the bone before and after the experiment, 

 one demonstrates that one third of the weight has disap- 

 peared ; this of course means that a third is animal matter, 

 and the remaining two thirds mineral matter. A bone that 

 has been burned is very brittle, and so the experiment like- 

 wise proves that the toughness and elasticity of bone are 

 due to the presence of animal ingredients. 



Action of Acid on Bones. In our study of digestion we 

 learned that insoluble mineral substances are dissolved by 

 the hydrochloric acid of the gastric juice. Hence, the hard 

 parts of bone can be removed by the action of this acid. 

 A rib bone that has been soaked in diluted hydrochloric 

 acid l for several days loses most of its rigidity, and while 

 retaining its shape, becomes very elastic and flexible. To 

 the mineral ingredients, therefore, bone owes its hardness 

 and rigidity for supporting the weight of the body. 



Nutritive Ingredients found in Bones. When pieces of large 

 soup bones are placed in water and heated slowly (on the 

 back of the stove) for several hours, a thick gelatinous mass 

 is formed. This is called soup stock. It contains most of 

 the fats, proteids, and other nutritive ingredients of bones, 

 and with the addition of vegetables and various condiments 

 makes a nutritious and palatable soup. Bones, therefore, 

 should not be regarded as refuse until after this nutrition 

 has been extracted. 



1 One part acid to six parts of water. 



