1906.] 0)1 The Physical Basis of Lifp. 405 



Matter is composed of molecules which in the liquid or solid state 

 are attracted to one another by forces of prodigious power. Each 

 molecule in the interior of a mass is pulled on the average equally in 

 all directions. But consider the surface layer, a film only a few 

 molecules deep. There the intermolecular forces are necessarily to a 

 great extent unbalanced, with the result that this surface lilm acts 

 something Uke a stretched elastic skin — it tries always to compress 

 the mass to the smallest possible dimension. This, however, is not 

 the only feature of the surface layer. It is also the layer which is in 

 contact with adjacent masses of matter, gas, liquid, or solid, as the 

 case may be. 



Now, masses of matter which do not mix when in contact, and 

 which therefore are defined by a surface of separation, are rarely, 

 perhaps never, without influence upon one another. Interaction of 

 the surface layer takes place, so that the balance of molecular forces 

 is modified, incomplete chemical reactions occur, and a condition of 

 molecular stress is produced which, amongst other things, is mani- 

 fested by the development of electrical charges. 



These molecular events on surfaces are very potent ; they can 

 produce effects which are impossible and even inconceivable in 

 matter in bulk. It is, for instance, not only possible, but probable, 

 that in the surface layers the conditions may sometimes be such as 

 to associate decrease of volume with decrease of pressure, a relation 

 so subversive of ordinary experience as to be unthinkable. In the 

 surface layer a gas may be condensed to the liquid state when far 

 above its critical temperature and below its critical pressure. Chemical 

 changes occur or are suspended under conditions of temperature 

 and pressure totally unlike those controlling the same changes in 

 masses of matter. Concentration, electric conductivity, all physical 

 properties in fact, become abnormal ; therefore, when the surface 

 energy forms a large fraction of the total molecular energy, as in 

 films, or fluid in fine capillaries, ordinary chemical or physical 

 knowledge fails us. 



There is no lack of evidence to prove that the lifelike character- 

 istics of colloidal matter, its capacity for storing impressions, the 

 elusiveness of its chemical and physical states, are due to the fact that 

 an exceptionally large fraction of its energy is in the form of surface 

 energy. 



There is also direct and unmistakable evidence in the nature of 

 the effect of various salts upon the heart-beat, and in the optical 

 characters of 'thin films, that living matter also contains a very large 

 proportion of surface energy per unit of mass, and the curious and 

 extreme physical and chemical powers which it manifests are without 

 doubt largely due to this cause. Now it is just in experiments on 

 surface energy that one finds a case analogous to the effect of the 

 salt in bringing about rejuvenescence of senile protoplasm, or in 

 awaking the dormant powers of an unfertilised iigg. 



