THE ANIMAL. XII. 



combustible matter derived from the food and the consequent 

 heat production do not occur there. It is not in the lungs 

 nor even in the blood that the combustion and formation of 

 carbon dioxide occur, but in the tissues themselves. 



Bones. Bone consists mainly of an earthy substance per- 

 meated by an albuminoid known as ossein. Bones are also 

 intersected by blood-vessels, nerves, &c. The marrow of bones 

 contains mainly fat and albumin. 



The proportion between the organic matter of bone and its 

 mineral constituents is liable to considerable variation according 

 to the quantities of blood-vessels, nerves, marrow, and water 

 which may be present. 



Usually from 30 to 50% of the weight of bone is lost on 

 burning. 



The inorganic matter left as ash consists mainly of calcium 

 phosphate, but includes also carbonates, chlorides, and fluorides 

 of calcium and magnesium. 



The following table gives the percentage composition of the 

 ash of bones of various animals": 



Man. Ox. Guinea-pig. 



Calcium phosphate ... 83-9 86'0 87'4 



Magnesium phosphate ... I'O I'O I'l 

 Calcium as carbonate, 



chloride, and fluoride 7' 6 7' 3 7'0 



Carbon dioxide ... 5-7 6'2 



Chlorine ... ... -2 -2 -1 



Fluorine -2 -3 



98-6 101-0 



The proportions of valuable manurial substances in bones 

 has already been given, f 



The Fatty Tissue. This consists of cells, the walls of 

 which are composed of a proteid substance resembling elastin, 

 filled with fat which, during life, is in the fluid state. The fat 

 consists mainly of glyceryl esters of stearic, oleic, palmitic, and 

 other fatty acids ; but, in addition, free fatty acids are present 



* Hammarsten, Physiological Chemistry, 239. t r. p. 135. 



