464 A NOTE ON ADSORPTION [ch. vi 



departures from symmetry may be correlated with the molecular 

 forces manifested in their fluid or semi-fluid surfaces. 



Looking at the physiological side, rather than at the morphological 

 which is more properly our own, we see how very important a 

 cellular system is bound to be, even in respect of its surface-area 

 alone. The order of magnitude of the cells which constitute our 

 tissues is such as to give a relation of surface to volume far beyond 

 anything in all the structures or mechanisms devised and fabricated 

 by man. At this extensive surface, capillary energy, a form of 

 energy scarcely utilised by man, plays a large predominant part in 

 the energetics of the organism. Even the warm-blooded animal is 

 not in reality a heat-engine; working as it does at almost constant 

 temperatures its output of energy is bound, by the principle of 

 Carnot, to be small. Nor is it an electrostatic machine, nor yet an 

 electrodynamic one. It is a mechanism in which chemical energy 

 turns into surface-energy, and, working hand in hand, the two are 

 transformed into mechanical energy, by steps which are for the 

 most part unknown*. 



We are led on by these considerations to reflect on the molecular, 

 rather than the histological, structure of the cell. We have already 

 spoken in passing of " monomolecular layers," such as Henri Devaux 

 imagined some thirty years ago, and afterwards obtained f, and 

 such as Irving Langmuir has lately made his own. The free surface 

 of every liquid (provided the form and symmetry of its molecules 

 permit) presents a single layer of oriented molecules. Such a surface 

 h no mere limit or simple boundary; it becomes a region of great 

 importance and peculiar activity in certain cases, when, for instance, 

 protein molecules of vast complexity are concerned. It is then 

 a morphological field with a molecular structure of its own, and a 

 dynamical field with energetics of its own. It becomes a frontier 

 where this alien molecule may be excluded and that other be passed 

 through: where some must submit to mere adsorption, and others 

 sufl'er chemical change. In a word, we begin to look on a surface-layer 

 or membrane, visible or invisible, as a vastly important thing, a place 

 of delicate operations, and a field of peculiar and potent activity. 



* Lippmann imagined a moteur electrocapillaire, unique in the history of 

 mechanical invention. Cf. Berthelot, Rev. Sci. Dec. 7, 1913. 



t CL{int. al.) H. Devaux, La structure moleculaire de la cellule vegetale, Bull. 

 Soc. Bot. de France, lxxv, p. 88, 1928. 



