THE FRAMEWORK OF THE BODY 53 



cavities called lacunce, connected by minute canals with 

 one another (Fig. 16, p. 25). Within the lacunae and 

 their canals are found little masses of protoplasm called 

 bone cells, or bone corpuscles. These branching bone cells 

 communicate with one another and with the blood vessels 

 of the Haversian canals. They are the architects for 

 building up the bony fabric. Each cell constructs walls 

 which unite with those about them to form the solid mass. 

 Along with the arteries of the interior bony structure 

 very fine nerve fibers have been traced, and lymph vessels 

 are found in connection with the blood capillaries within 

 the substance of all bones. 



60. Hygiene of Bones and Joints. The science of hygiene 

 has to do with all that promotes normal action of the 

 various parts of the body and of the whole mechanism. 

 In respect to the bones we need to consider first the con- 

 ditions most favorable to their growth. 



61. Bones of the Young. As the skeleton grows it not 

 only becomes larger, but also becomes changed in the struc- 

 ture of its parts. The bones of an infant are almost wholly 

 composed of cartilage, having the form of the completed 

 bone, but the flexibility and elasticity of the cartilaginous 

 tissue. They become slowly more firm and hard by a 

 deposit of solid material furnished by the food, selected 

 from the blood and lymph by the living cells in the carti- 

 lage and the periosteum. As the bone is built up by the 

 deposit of the salts of lime (chiefly calcium phosphate), 

 which furnish nearly all the earthy part of bone, the carti- 

 lage cells waste away, and their dead matter is carried oft' 

 by the blood. 



62. Importance of Proper Food. It is evident that the 

 food suitable for young children must contain lime and 

 phosphorus in proper proportions for making bone. Milk 



