38 HUMAN PHYSIOLOGY 



One important function performed by the cartilage is in 

 bringing about the increase in length of the bones. In 

 addition to the centre of ossification in the shaft, at each 

 end of the bone one or more similar centres of ossification 

 form. These are the epiphyses. Between these and the 

 central rod of bone the diaphysis a zone of cartilage 

 exists until near adult life, when the bones stop growing. 

 In this zone, the cells arrange themselves in vertical rows, 

 divide at right angle to the long axis of the bone, and form 

 cartilage. This cartilage as it is formed is attacked by the 

 bone-forming changes at the diaphysis and epiphyses, but 

 the amount of new cartilage formed is proportionate to this, 

 and thus a zone of growing cartilage continues to exist until 

 early adult life, when epiphyses and diaphysis join and 

 growth in length is stopped. The rate and extent of this 

 growth of the cartilage has an important influence on the 

 growth of the individual. 



(2) CHEMISTRY. The composition of adult bone is roughly 

 as follows : 



Water, 10 per cent. 

 Solids, 90 per cent. 



Organic, 35 per cent. chiefly collagen. 

 Inorganic, 65 per cent. 

 Calcium phosphate, 51. 

 carbonate, 11. 



fluoride, 0*2. 



Magnesium phosphate, 1. 

 Sodium salts, 1. 



The points to be remembered are the small amount of 

 water, the large amount of inorganic matter, chiefly calcic 

 phosphate, and the nature of the organic matter collagen. 



(B) THE MASTER TISSUES OF THE BODY, 

 MUSCLE AND NERYE. 



By means of the epithelial and connective tissues the 

 body is protected, supported, and nourished. It performs 

 purely vegetative functions, but it is not brought into 

 relationship with its environments. By the development 



