QUESTIONS AND ANSWERS 105 



What are the physical properties of bone? How does the chemical 

 composition of bone vary with age? 

 Bones are composed of an outer layer of compact tissue and of a 

 spongy, reticular tissue which forms the interior (marrow). The 

 compact tissue is traversed by channels called "Haversian canals," 

 from which radiate numerous canaliculi ; the latter are surrounded 

 by concentric lamellae of bone, separated by spaces (lacunae) con- 

 taining the bone cells, corpuscles. These lacunse communicate with 

 the Haversian canals through the canaliculi. The inner spongy tis- 

 sue contains large marrow cavities. The exterior of bone is covered 

 by a thin, tough, protective membrane, the periosteum. 



As age advances, the bones contain less organic matter and more 

 of the inorganic constituents. 



Give the composition of bone. State how bone is nourished and give 

 the function of long bones. 



See answer to preceding question. 



Bones consist of connective tissue, the substratum of which is 

 osseine (an animal matter which yields gelatin upon boiling), 

 impregnated with lime salts, chiefly calcium phosphate. Bone is 

 composed of one-third animal matter and two-thirds mineral mat- 

 ter. Nourishment is supplied to bone by a nutrient artery which 

 sends branches into the medullary and Haversian canals. 



Long bones serve an important part in locomotion by imparting 

 rigidity to the limbs and furnishing muscular attachments, as well 

 as by entering into the formation of joints. 



Mention the functions of the articular cartilages. 



1. Favor, by their smoothness, the gliding and displacement of 



bones. 



2. By their suppleness and elasticity, they lessen the violent 

 shocks to which the articulations are exposed. 



3. They resist the wear and deformations of the articular sur- 

 faces. 



Mention with regard to the body (a) the principal secreting organs, 

 (b) the excreting organs, (c) the vital organs. 



(a) Salivary glands, gastric glands, liver, pancreas, sebaceous 

 glands, synovial, mucous and serous membranes, lachrymal glandi 

 The spleen, thymus, thyroid and adrenals have an internal secretion. 



(b) Skin, kidneys, bowels and lungs. 



(e) Heart, lungs, brain, intestines, liver, kidneys. 



