8 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
of minimal surface-energy. Among the conclusions to 
which it leads are the following : 
1. Dissolved substances which lower the tension at a 
given surface will be more concentrated near it than in 
regions remote from it, and those which raise the surface- 
tension will tend to migrate from that surface so that there 
will be less there. 
2. Chemical or physico-chemical changes which result 
in products lowering the tension at a given surface will 
tend to proceed further and take place at a faster rate there 
than in regions remote from that surface, and those which 
raise the tension will be diminished and slower. Among 
physico-chemical changes may be_ specially mentioned 
hydrolysis and ionisation. 
On testing the various substances which in watery 
solution had yielded mechanical surface aggregates, it was 
found that all of them did lower the tension of the air 
surface of water, and therefore fulfilled the condition 
necessary to explain their surface concentration on the 
Gibbs-Thomson principle. ‘That principle does not by itself 
suffice to explain the minute details of the observed 
phenomena; it does not explain why soluble substances pass 
actually out of solution nor, as Professor Lewis has shewn, 
account quantitatively for their concentration, but at least 
it takes us a long way in the right direction. And it offers 
many possibilities for explaining the fact that in some cases 
the mechanical surface aggregates are chemically different 
from the original substance in solution, as for example with 
egg albumin. 
It was further clear that on the Gibbs-Thomson 
principle increased concentrations of appropriate initially 
dissolved substances were also to be expected at the inter- 
faces between two immiscible liquids. It was in many cases 
very easy to demonstrate that abnormal rigidity or Plateau 
