NATURE OF PROTOPLASMIC RESPIRATION. 333 



The formula for the rusting of iron on this hypothesis would 

 be as follows : 



II. 4H -f O 2 = 2H 3 O or 

 2H + O 2 = H 2 O 2 

 H 2 O 2 + Fe = FeO + H 2 O 



Reaction I. cannot go on unless oxygen is present to remove 

 the nascent hydrogen. If no oxygen is present the nascent 

 hydrogen at once reduces the iron oxide and forms metallic iron 

 again. The atmospheric oxygen does not unite with the iron, 

 but with the hydrogen. 



The same hypothesis will explain protoplasmic respiration and 

 at once makes clear the identity of anaerobic and aerobic respira- 

 tion. The following theory of respiration is founded in part on 

 Armstrong's work.. 



The real respiration of all forms of protoplasm, both aerobic 

 and anaerobic, is brought about not by the oxygen of the air, but 

 by that of the water. The hydrogen set free from the water 

 combines with other elements of the protoplasm, thus keeping it 

 reduced ; it also combines with the oxygen of the air if this is 

 present to form water ; and in the absence of oxygen it may 

 escape as free hydrogen. 



The only difference between anaerobic and aerobic respiration 

 is that the anaerobic protoplasm is so powerful a reducing agent 

 that it is able to drive hydrogen out of the water, thus oxidizing 

 itself without the aid of atmospheric oxygen to act as a depolarizer. 

 ^Erobic protoplasm being less powerfully reducing requires the 

 presence of more or less oxygen to take care of the hydrogen- 

 The difference between these different kinds of protoplasm is 

 exactly the difference between metallic sodium and metallic iron. 

 Sodium is so powerful a reducing agent that it oxidizes itself at 

 the expense of water driving out hydrogen even in an atmos- 

 phere of hydrogen. This corresponds to anaerobic protoplasm : 



Na + HOH = NaOH + H 



Iron is so weak a reducing agent that it requires the presence 

 of free oxygen to take care of the hydrogen set free, before it 

 will oxidize itself. This corresponds to aerobic respiration. Pro- 



