66 



NATURE 



[September i6, 19 15 



It is important to remember that organisation neces- 

 sarily requires someone to tal<:e the lead and someone 

 to fill the subordinate's place ; otherwise, all is 

 anarchy, and whatever may be the discipline within 

 each society, their relations to one another at present 

 can but be described as anarchy ; the fellow of the 

 Royal Society has no more responsibility at present 

 than any member of the smallest debating club; his 

 selection is regarded as an honour, but an honour is 

 as meaningless as an iron cross if it does not imply 

 responsibility and an opportunity for more work. 

 What applies to an individual applies to a society of 

 such persons. The premier position of the Royal 

 Society is acknowledged by every British worker in 

 science, and those societies which similarly embrace 

 all phases of science can assist the aims of organisation 

 by reminding the Royal Society that its position is 

 more than ornamental, and that its lead will be 

 welcomed. 



SECTION I. 



physiology. 



Opening Address by Prof. W. M. Bayliss, 



M.A., D.Sc, F.R.S., President of the Section. 



The Physiological Importance of Phase Boundaries. 

 Even a hasty consideration of the arrangements 

 present in living cells is sufficient to bring conviction 

 that the physical and chemical systems concerned 

 operate under conditions very different from those of 

 reactions taking place between substances in true 

 solution. We become aware of the fact that there 

 are numerous constituents of the cell which do not 

 mix with one another. In other words, the cell 

 system is one of many "phases," to use the expres- 

 sion introduced by Willard Gibbs. 



Further, parts of this system which appear homo- 

 geneous under the ordinary microscope are shown by 

 the ultra-microscope to be themselves heterogeneous. 

 These are in what is known as the colloidal state. 

 Some dispute has taken place as to whether this state 

 is properly to be called a heterogeneous one, but it 

 is sufficient for our purpose to note that Investigation 

 shows that the interfaces of contact between the com- 

 ponents of such systems are the seat of the various 

 forms of energy which we meet with in the case of 

 systems obviously consisting of phases which can be 

 separated mechanically, so that considerations apply- 

 ing to coarsely heterogeneous systems apply also to 

 colloidal systems. Although the phases of a colloidal 

 system cannot be so obviously and easily separated 

 as those of an ordinary heterogeneous one, this can 

 be done almost completely by filtration through mem- 

 branes such as the gelatin in Martin's process. To 

 avoid confusion, however, it has been suggested that 

 the colloidal state should be spoken of as "micro- 

 heterogeneous." There are, in fact, certain pheno- 

 mena more or less peculiar to the colloidal state and 

 due to the influence of the sharp curvature of the 

 surfaces of the minutely subdivided phase. The effect 

 of this curvature is a considerable pressure in the 

 interior of the phase, owing to the surface tension, 

 and It adds further complexity to the properties 

 manifested by It. 



We see, then, that the chemical reactions of chief 

 importance to us as physiologists are those known • 

 as "heterogeneous." This class of reactions, until 

 comparatively recent times, has been somewhat 

 neglected by the pure chemist. 



In some of its aspects, the problem before us was 

 discussed by one of my predecessors, Prof. Hopkins, 

 as also by Prof. Macallum, but its importance will, 

 I think, warrant my asking your indulgence for a 



NO. 2394, VOL. 96] 



further brief discussion. Permit me first to apologise 

 for what may seem to some of those present to be 

 an unnecessarily elementary treatment of certain 

 points. 



It is easy to realise that the molecules which are 

 situated at the interface where two phases are in con- 

 tact are subject to forces differing from those to 

 which the molecules in the interior of either phase 

 are subject. Consider one phase only, the molecules 

 at its surface are exposed on the one side to the 

 influence of similar molecules; on the other side, they 

 are exposed to the influence of molecules of a nature 

 chemically unlike their own or in a different physical 

 state of aggregation. The result of such asymmetric 

 forces is that the phase boundary is the seat of various 

 forms of energy not present in the interior of the 

 phase. The most obvious of these is the surface 

 energy due to the state of tension existing where a 

 liquid or a gas forms one of the phases. It would 

 lead us too far to discuss the mode of origin of this 

 surface tension, except to call to mind that it is due 

 to the attractive force of the molecules for one another, 

 a force which is left partially unbalanced at the sur- 

 face, so that the molecules here are pulled inwards. 

 The tension is, of course, only the intensity factor 

 of the surface energy, the capacity factor being the 

 area of the surface. We see at once that any influence 

 which alters the area of the surface alters also the 

 magnitude of that form of energy of which we are 

 speaking. 



This is not the only way in which the properties of 

 substances are changed at phase boundaries. The 

 compressibility of a solvent, such as water, are altered, 

 so that the solubilities of various substances in it 

 are not the same as in the Interior of the liquid phase. 

 It Is stated by J. J. Thomson that potassium sulphate 

 is 60 per cent, more soluble in the surface film. The 

 ways in which the properties of a solvent are changed 

 are sometimes spoken of as "lyotropic," and they 

 play an important part in the behaviour of colloids. 

 We meet also with the presence of electrical charges, 

 of positive or negative sign. These are due, as a rule, 

 to electrolytic dissociation of the surface of one phase, 

 in which the one ion, owing to its insolubility, re- 

 mains fixed at the surface, while the opposite ion, 

 although soluble, cannot wander away further than 

 permitted by electrostatic attraction. Thus we have a 

 Helmholtz double layer produced. 



Before we pass on to consider how these phenomena 

 intervene in physiological processes, there is one fact 

 that should be referred to on account of its significance 

 in connection with the contractile force of muscle. 

 Surface tension is found to decrease as the tempera- 

 ture rises, or, as it is sometimes put, it has a negative 

 temperature coefficient. This Is unusual; but, if we 

 remember that the interface between a liquid and its 

 vapour disappears when the temperature rises to the 

 critical point, and with It, of course, all phenomena 

 at the boundary surface, the fact is not surprising 

 that there is a diminution of these phenomena as the 

 critical temperature Is approached. 



Perhaps that result of surface energy known as 

 "adsorption" is the one in which the conditions 

 present at phase boundaries make themselves most 

 frequently obvious. Since the name has been used 

 somewhat loosely, it Is a matter of some consequence 

 to have clear ideas of what is meant when It is made 

 use of. Unless it Is used to describe a definite fact, 

 it can only be mischievous to the progress of science. 

 Permit me, then, first to remind you of that fact 

 of universal experience, known as the "dissipation , 

 of energy," which is involved in the second law of 

 energetics. Free energy — that is, energy which can 

 be used for the performance of useful work — is in- 



