112 THE THEORY OF IONS 



seen in the serum and tissue fluids, in being more 

 unstable or having a greater tendency to intra- 

 molecular change. We have already seen that this 

 instability is ascribed by Pfliiger to the presence of 

 cyanogen, and by Latham to cyanhydrines in the 

 molecule. But it is claimed by Verworn that the 

 changes are due to the introduction of oxygen into 

 the biogen molecule, which he considers has a side- 

 chain of an aldehyde character to act as an oxygen 

 receptor. Loew considers that instability to be 

 due to the simultaneous presence of an aldehyde 

 and amino-acid groups in the molecule. He be- 

 lieves that in the living proteid they are separate, 

 and that when they combine the protoplasm dies or 

 is changed into a stable, non-living proteid. 



The oxidations which occur in living protoplasm 

 are explained differently. If the protoplasmic proteid 

 is not indifferent to neutral oxygen, there may be a 

 cleavage of the oxygen molecule whereby the living 

 proteid is oxidised by one of the ions, the other ion 

 being free to act upon more difficultly oxidisable 

 substances by a secondary operation. Another 

 widely different theory is that reducing substances 

 are formed by the protoplasm, which split the neutral 

 oxygen molecule, uniting with one and setting the 

 other free. The cells of animal tissues and organs 

 have the property, like the cells of lower organisms, 

 of splitting dys-oxidisable substances into such as are 

 more easily oxidisable, perhaps with the production 

 of nascent hydrogen. The oxidation of the readily 

 oxidisable substances as produced by ionisation of 

 oxygen leads to the secondary oxidation of the less 

 oxidisable ones ; and the products undergo further 



