THE ATMOSPHERE 205 



gains the mastery over and expels C0 2 . The latter gas is 

 returned to the atmosphere through volcanic fissures. Bunge 

 likewise suggests that the percentage of oxygen is lessening. 

 Ferrous oxide arises as a product of the decomposition of certain 

 silicates, and this combines with oxygen to form ferric oxide. 

 The ferric oxide is decomposed in the presence of rotting organic 

 matter and the oxygen returned to the atmosphere combined as 

 C0 2 . Plant life, either living or rotting, seems to be the sole 

 means by which oxygen is set free, and it is doubtful whether 

 all the oxygen returns to the atmosphere, which is combined 

 in the processes of respiration, combustion, and in the oxidation 

 of iron and sulphur. 



As the earth cools and its crust consolidates, Bunge supposes 

 more and more C0 2 will become fixed, and if this fixation is 

 unbalanced, life must finally cease. There is, however, another 

 source of C0 2 the bicarbonate of lime dissolved in sea-water. 

 When the tension of C0 2 in the air falls, bicarbonate becomes 

 dissociated into carbonate and C0 2 . The process reverses 

 when the tension rises. Thus the amount of C0 2 is kept 

 constant, and Bunge's prophecy can be discarded. In the 

 sea it is estimated there is 27 times as much C0 2 as in 

 the atmosphere, and that an additional O'l per cent. C0 2 in the 

 atmosphere would lead to the absorption by the sea of 3' 8 5 x 10 

 tons in one year (A. Krogh). 



Without a due supply of nitrogenous food living matter 

 cannot carry on the processes of growth the building of skeletal 

 structures and the storage of food-stuffs. In the higher plants 

 nitrogen appears to be employed almost entirely for the building 

 of organ proteid, while carbohydrate is used for skeletal structures 

 e.g. bark, store of this being easily obtained. 



Saprophytes and parasites living in plenteous supplies of nitro- 

 genous matter build with chitin in place of cellulose. Animals use 

 both nitrogenous and carbohydrate matter as sources of kinetic 

 energy, and in them a daily output as well as intake of nitrogen 

 occurs. Nitrogenous matter as a source of energy is wasteful, for 

 only the carbohydrate moiety is required. The higher plants 

 obtain energy from the combustion of carbohydrate, and with the 

 possible exception of the alkaloids, do not excrete nitrogen. 

 Nitrogenous matter is used as a source of energy in the decom- 

 position of organic nitrogenous matter by numerous kinds of 



