November 3, 1923] 



NA TURE 



671 



Physical Chemistry and Physiology at the British Association. 



Interfacial Phenomena. 



T N the Physiology Section, at the recent meeting of 

 *• the British Association at Liverpool, important 

 commxunications on this subject were given by Prof. 

 W. Ramsden and collaborators, and some remarkably 

 pretty demonstrations were shown. 



Mr. J. R. Bruce and Prof. W. Ramsden showed that 

 egg-albumin became irreversibly coagulated at the 

 gas-water surface, even when all such mechanical 

 disturbances as could compress the adsorbed protein 

 film laterally were strictly excluded. The solubility 

 or insolubility of the adsorptum was ascertained in 

 situ by subjecting the rigid adsorption surface to 

 three different treatments : — (i) it was washed from 

 below with large volumes of water ; (2) bile salt was 

 introduced into the depths of the underlying solution ; 

 (3) it was made continuous with a surrounding sur- 

 face of water maintained in a clean condition and of 

 full normal surface-tension. If the surface rigidity 

 persisted, it was argued that the adsorbed protein 

 liad lost its initial solubility. It was concluded that 

 with egg - albumin coagulation took place by the 

 catalytic influence of surface - conditions, and that 

 gross mechanical factors played no essential part, — 

 " mechanical surface coagula " should be termed 

 " mas.sed surface coagula." 



True coagulation was a dehydrating condensation 

 of the amino and carboxyl groups of large numbers of 

 neighbouring protein molecules. Metaprotein forma- 

 tion was a precisely similar condensation of a rela- 

 tively small number of molecules. The size of the 

 complexes formed depended mainly on the concentra- 

 tion of the protein at the time when the reacting 

 groups were activated. Protein adsorbed at a 

 gas/water interface was highly concentrated and the 

 denaturation which followed resulted therefore in 

 the production of coagulated protein. It was also 

 shown (by method 3) that egg -albumin, fibrinogen 

 and edestin became irreversibly coagulated within less 

 than five seconds of attaining a gas-water surface. 



Mr. J. Brooks and Prof. W. Ramsden showed that 

 interfaces between water and benzene or water and 

 paraffin in the presence of various emulsifying soluble 

 solids were in some cases mobile, in others rigid. The 

 existence of such mobility showed that Bancroft's 

 theory that stabilisation of emulsions was effected by 

 a continuous emulsifying shell with two different 

 surface tensions on its two faces was in need of 

 important modification. 



In cases where the emulsifying substance consisted 

 of insoluble solids in fine suspension, evidence was 

 given thn* '' " ' ';icf factor determining which of the 

 two li(]iii 10 dispersed in the other was the 



angle oi . .....i.. formed between the liquid-liquid 



interfaces and the sides of discrete solid particles. 

 Methods were given for ascertaining in which of the 

 two liquids the angle of contact was obtuse, and it 

 was found that in every case it was this liquid which 

 became dispersed in the other. 



The demonstrations, given by Prof. W. Ramsden 

 and Miss A. Mackenzie, to illustrate experiments on 

 surface-films, were very beautiful. One simple ex- 

 periment to illustrate the rigidity of surface-films in 

 certain cases can easily be repeated by any one : a 

 light magnet is floated on the surface of a saponin 

 solution, and an ordinary pivoted magnetic needle 

 immersed in the same solution. On bringing a 

 magnet near to the vessel, the surface magnet 

 remains stationaiy, while the immersed one follows 

 the movements of the magnet outside just as readily 

 as it would do in air. 



NO. 2818, VOL. I 12] 



As Prof. Donnan pointed out in his presidential 

 address to the Section of Chemistr>^ many substances 

 spread on water surfaces to a stable film, one molecule 

 thick. All the molecules appear to be oriented 

 parallel to one another and perpendicular to the 

 surface. Mr. N. K. Adam, who has employed this 

 method for the determination of the cross-sectional 

 area of molecules, gave a demonstration at the 

 scientific soiree of the method of procedure. He has 

 been able further to show that these surface films 

 possess, according to the conditions, the properties of 

 solids, liquids, or gases, a fact of the greatest theoretical 

 significance. 



The Properties of Membranes. 



A joint discussion on " The Physical Chemistry of 

 Membranes in Relation to Physiological Science "'was 

 held by the Chemistry and Physiology Sections, and 

 was opened by Prof. H. E. Roaf. A membrane was 

 defined as a structure separating two phases ; it 

 might be semi-permeable or show permeability of 

 varying grade, and the presence of the membrane 

 made it necessary to consider the po.ssibility of the 

 occurrence of filtration, osmosis, electro-endosmosis, 

 and other related phenomena, for the membrane 

 limited diffusion and allowed differences of concentra- 

 tion of solutes on its two sides, giving rise to various 

 osmotic and electrical phenomena. Physiology was 

 largely concerned with the problem of the passage 

 of material across physiological membranes : as 

 example of these the lungs, intestine, kidney, and 

 salivary gland might be taken. 



In the lungs, there appeared to be no certain 

 evidence that the membranes which had to be tra- 

 versed by the gases entering and leaving the blood did 

 anything but slightly hinder diffusion — the state of 

 equilibrium between blood and air was almost 

 attained, and oxygen never reached a higher partial 

 pressure in the blood than in the air, nor did carbon 

 dioxide ever have a greater pressure in the air of the 

 alveoli than in the blood. Diffusion was adequate to 

 explain not only the partial pressures found in blood 

 and air, but also sufficed to account for the total 

 amounts of oxygen and carbon dioxide traversing the 

 membrane under all conditions. 



The passage of substances across the membrane of 

 the intestine offered a much more diflicult problem, 

 and one towards the solution of which we had made 

 much less progress, for here many facts seemed to 

 be in opposition to the view that mere diffusion was 

 the chief or even an important factor. When the 

 epithelium was removed from the mucosa of the small 

 intestine, for example, absorption of its (cm tents into 

 the blood was slower, not quicker. Again, blood 

 plasma could be absorbed completely from the lumen 

 of the bowel into the blood, in spite of the apparent 

 identity of the contents with the fluid part of the 

 blood. Finally, when absorption took place from 

 the bowel, the oxygen usage of the bowel had been 

 stated to be increased, i.e. more work was being done 

 by it under these conditions. 



The kidney and the salivary gland presented equal 

 difficulties ; that considerable work was done bv the 

 kidney in concentrating those blood constituents 

 which were excreted, was indisputable. Similarly, 

 the salivary glands could not act by any mere filtra- 

 tion, because, apart from the chemical differences 

 between the blood and the saliva, there was the fact 

 that the pressure reached in the salivary ducts when 

 the flow was stopped by occlusion was, as Ludwig 

 showed, much greater tlinn iho mrixiinuiu arterial 



