NUTRITION OF BONES 241 



ness. All bones have this compound structure, those 

 in which the lime is most abundant being stiffer than those 

 in which the cartilage predominates. Bones of old per- 

 sons contain less cartilage and more lime than those of 

 young people, and hence break more easily. 



If we saw a soup bone lengthwise and boil it in water 

 there will appear on the surface a rich collection of oil 

 drops. These come from the marrow of the bone, which is 

 very rich in fats. If, now, the water in wliich the bone 

 was boiled is allowed to cool, a solid, jeUylike mass forms 

 whose jellylike character is due to the presence of albuminoid 

 material. This albuminoid material, usually in the form of 

 gelatin, forms the nutrient portion of soups. Food tests 

 also show that bones contain a small proportion of other 

 nutrients and some flavoring material, and when such a 

 mixture is combined with vegetables the combination makes 

 a very nutritious food. Bones alone, however, are not to 

 be considered as very rich in nutrient material. 



Nutrition of bones. — The bones of a child are much 

 richer in cartilage than those of an adult. As the child 

 grows to an adult the bones increase in size and in mineral 

 matter. The manner in which this growth takes place 

 becomes clear only when we understand the relation of 

 the bone structure to the circulatory system. A glance 

 at the microscopic structure of bone shows it to be pene- 

 trated by a series of canals (the Haversian canals) by means 

 of which the blood vessels of the periosteum are able to 

 penetrate to aU parts of the bone. From these canals the 

 blood is enabled to radiate by a series of cross channels, 

 or canaliculi. These canaliculi are at right angles to the 

 canals, and connect them with a series of cavities called 

 the lacunae which are arranged in concentric circles about 



EDDY. PHYS. — 16 



