THE CHEMISTRY OF THE ANIMAL BODY 157 



with carbon it yields its own volume of carbon dioxide, but 

 in respiratioil the increase in volume of the carbon dioxide 

 is less than the decrease in that of oxygen, being generally 

 about 90 per cent, of that decrease. This is probably due 

 to some of the oxygen being used to oxidise some hydrogen of 

 the food or tissues to water. Though the absorption of oxygen 

 takes place almost wholly in the lungs, it is not there that the 

 act of combination of the carbon and hydrogen of the body 

 with the oxygen takes place. The blood, by the haemoglobin 

 of the red corpuscles, acts as a carrier of oxygen, and the actual 

 combustion of the products derived from the food occurs in the 

 tissues themselves. 



Bones consist essentially of an earthy framework composed 

 mainly of calcium phosphate, permeated by an albuminoid 

 known as ossein, and by nerves, blood-vessels, tfec. In the 

 hollow centre of many bones is the marrow^ which consists 

 largely of fat and albuminoids. The relative proportions of 

 mineral and organic matter in bones vary considerably. The 

 latter usually varies from 30 to 50 per cent, of the weight 

 of the whole bono. The proportions of nitrogen and phos- 

 phate of lime in avernge bones have already been discussed 

 in the chapter on manures. 



The ash of bones, however, is not entirely phosphate of 

 lime, but contains also carbonates, fluorides, chlorides and 

 magnesia. An analysis of the ash of ox-bones gave : 



Calcium phosphate 86*0 



Magnesium phosphate 1-0 



Calcium as carbonate, chloride and fluoride . 7-3 



Carbcn dioxide 6 2 



Chlorine . . . . ; . . . 0*2 



Fluorine 0*3 



101-0 



Muscular tissue consists largely of albuminoids and water, 

 but contains also small quantities of fat, glycogen (or animal 

 starch), '* nitrogenous extractives " of which creative, CJi^yfi^y 

 sarcitis, C^H^N^O, xanthine, C^li^Np^, guanine, CjII^N^^O and 



