Hans Burstrom 255 



peated such exchanges for hydrogen ions and ultimately reach the 

 /-level. Repeated exchanges of this kind must take place to secure 

 the adsorption equilibria as the cations are withdrawn from the col- 

 loidal system through combination with the released anions at the 

 /'-level. Thus, the driving force for the intake and accumulation of 

 salts is the absorption of anions which is caused by the passage of 

 electrons to the plasma surfaces. 



The central problem then becomes to ascertain whether we are 

 correct in assuming such a unidirectional wave of electrons. Lundegardh 

 answers this question in the affirmative. The transport of electrons by 

 cytochromes is a well-known part of the iron-catalyzed respiratory 

 system, one end of which is the oxidation by the atmospheric oxygen 

 of ferrous iron carrying one electron in excess. In fact, the oxidation 

 requires that the ferrous iron give off its electron to the oxygen, which 

 combines with hydrogen ions to form water. This is the formation of 

 water which occurs in the respiration. This oxidation, Lundegardh 

 postulates, ought to take place at the o-level, because oxygen is supplied 

 from the external solution, and there must be a falling oxygen gradient 

 from the o- to the /-level. The other end of the respiration, involving 

 dehydrogenations of the respired substrate, is a reduction process and 

 may be restricted to loci of low oxygen tension, which means the /-level. 

 Electrons must be given off there and carried through the cytoplasm 

 to the o-level. We get as a consequence the postulated transfer of elec- 

 trons, and thus the whole mechanism is made possible. The production 

 of electrons is caused by the splitting of the substrate as a normal part 

 of respiration which together with the oxidation at the o-level appears 

 as the salt respiration. In this way it is clear that the absorption of 

 anions is directly connected with the process of respiration. 



Such a picture involves a fixed polar organization of the cytoplasm 

 in accordance with the oxygen gradient, for which we have no direct 

 evidence. It is absolutely necessary, however, for any theory of ion 

 absorption to assume a polarity within the cell, and this one seems to 

 be both very simple and well founded. The ultimate controlling factor 

 of the absorption and accumulation of ions is then the oxygen gradient 

 in the cell. 



The theory of Robertson is in its main features very similar to that 



