THE CHEMISTRY OF THE ANIMAL BODY. 945 



combination as oxyhaemoglobin. It is present dissolved in the saliva, so great 

 is the amount of oxygen furnished by the blood to the salivary gland ; it 

 is, however, not found in the urine or in the bile. 



Preparation. (1) Through the electrolysis of water (see Hydrogen). 



(2) By heating manganese dioxide with sulphuric acid, 



2MnO, + H 2 SO< = 2MnS0 4 + 2H 2 + O a . 



(3) By heating potassium chlorate, 



(4) By the action of a vacuum, or an atmosphere containing no oxygen, on 

 a solution of oxyhaeruoglobin, 



Hb-O 2 =Hb + 2 . 



This latter is the method occurring in the higher animals. Any oxygen present 

 in a cell in the body combines with the decomposition products formed there, 

 consequently entailing in such a cell an oxygen vacuum, which now acts upon 

 the oxyhaemoglobin of the blood-corpuscles in an adjacent capillary, dissociating 

 it into oxygen and hemoglobin. 



(5) By the action of sunlight on the leaf of the plant, transforming the 

 carbonic oxide and water of the air into sugar, and setting oxygen free, 



6CO 2 + 6H 2 O = C 6 H 12 O 6 + 6O 2 . 



Properties. All the elements except fluorine unite with oxygen, and the 

 products are known as oxides, the process being called oxidation. It is usually 

 accompanied by the evolution of energy in the form of heat, and often the 

 energy liberated is sufficiently great to cause the production of light. The 

 light of a candle comes from vibrating particles of carbon in the flame, which 

 particles collect as lampblack on a cold plate. In pure oxygen combustion is 

 more violent than in the air ; thus, iron burns brilliantly in pure oxygen, while 

 in damp air it is only very slowly converted into oxide (rust). This latter 

 process is called slow combustion, and animal metabolism is in the nature of a 

 slow combustion. In the burning candle has been noted the liberation of heat, 

 and motion of the smallest particles : in the cell there is likewise oxidation, with 

 dependent liberation of heat and motion of the smallest particles in virtue of 

 which the cell is active. Phenomena of life are phenomena of motion, and 

 the energy supplying this motion comes from chemical decomposition. The 

 amount of oxidation in the animal is not increased in an atmosphere of pure 

 oxygen, nor, within wide limits, is it affected by variations in atmospheric 

 pressure, for oxygen is not the cause of decomposition. In putrefaction it is 

 known that bacteria cause decomposition, and the products subsequently unite 

 with oxygen. But the cause of the decomposition in the cell remains unsolved, 

 it being only known that the decomposition-products after being formed unite 

 with oxygen. So the quantity of oxygen absorbed by the body depends on the 

 decomposition going on, not the decomposition on the absorption of oxygen. 

 This distinction is fundamental (see further under Ozone and Peroxide of 

 Hydrogen). 



