and Bio-electricat Phenomena. 
681 
ions may very probably be maintained in the oil at a nearly constant 
concentration, while transference of potassium ions takes place mainly as 
undissociated salt. If this be an adequate explanation, Dr. Beutner may 
fairly claim justification for the view that the solubility of salts is the pre¬ 
dominating factor in the production of differences of potential in his systems, 
although the differences of hydrogen-ion concentration which arise must 
also be taken into account; but his quantitative results must in this case be 
entirely invalidated, since changes of conductivity will be mainly due to the 
production and solution of hydrogen chloride. Moreover, as has been 
already remarked, there appears in many cases to be no adequate reason 
for assuming the absence of a diffusion potential. 
On more general questions there is little to be added to what has already 
been said—the value of an adequate model of the cell in its electrochemical 
relations cannot be doubted, but until we know more of cell mechanism the 
attempt to construct such a model would appear premature and liable to 
mislead. This is said with no desire to underrate the value of attempts to 
draw analogies between physical and biological systems; such analogies 
constitute the chief hope of advance upon the biological side, but it must be 
remembered that their interpretation is beset with all the difficulties which 
arguments from analogy admittedly encounter. Dr. Beutner attaches great 
importance to Macdonald’s experiments on dissected nerves. It may well 
be true that the nerve-sheath, which is known to contain much lipoid sub¬ 
stance, plays a part similar to that of the waxy cuticle of the apple, and that 
Dr. Beutner’s acid-oil systems are typical of both. This is undoubtedly 
important, but since both of these are very special structures it is hardly 
a justification for the assumption that the differences of potential at all cell 
surfaces are solely conditioned by differential solubility in a lipoid layer 
which contains free acid, especially in view of the fact that the lipoid theory 
has been universally rejected by physiologists after a very large amount of 
investigation. Dr. Beutner’s treatment of the ‘ current of injury ’, and the 
fact that he deduces the distribution of fatty acid in the apple from this 
phenomenon, are evidence of the large claim of universal validity which he 
makes for his hypothesis. It should perhaps be added that the statement as 
to a homogeneous ‘flesh’ to which Dr. Beutner objects was based on his 
treatment of the ‘ flesh ’ as a separate phase. 
