152 THE POPULAR SCIENCE MONTHLY 



tion of hydrogen peroxide is poured over the surface of pure mercury, 

 a film of peroxidate at once forms over the surface of the metal. Its 

 formation alters the surface-tension of the mercury by changing the po- 

 tential-difference between the metal and the solution. Consequently, 

 the form of the mercury-surface changes. Under appropriate conditions 

 this deformation causes a mechanical rupture of the film at some por- 

 tion of its surface; there follows on this an electrolytic decomposition 

 of the peroxidate at the margin of the fissure, an effect which spreads 

 over the whole surface and involves the dissolution of the film, and its 

 reduction to metallic mercury, together with the liberation of oxygen. 

 The film then reforms, and the process is repeated. Thus a regular 

 rhythm, involving a form-change, a chemical decomposition, and a 

 change of electrical polarization, is started and continues automatically. 

 The rate of rhythm may be altered, just as in organic processes, by 

 altering the chemical character of the medium, e. g., by changing its 

 alkalinity, or by the addition of various other chemical substances. The 

 velocity with which the film is laid down and dissolved may thus be in- 

 fluenced, and the whole rhythm correspondingly affected. Graphic 

 records showing the variation in the rate of oxygen-liberation present a 

 marked resemblance to the records of rhythmical organic processes like 

 the heart-beat. Now the general conditions determining the rhythm in 

 this phenomenon are strikingly like those which, on the foregoing theory 

 of stimulation, determine the physiological rhythms. The surface- 

 film of peroxidate may be compared to the plasma-membrane. Its rup- 

 ture is equivalent to a local increase of permeability. This change is 

 the direct condition both of the chemical change and of the electro- 

 motor change, on which last depends the variation of surface-tension 

 conditioning the form-change. While the living system is indefi- 

 nitely more complex than the mercury-peroxide system, yet in its 

 rhythmical character and in the essential nature of the controlling con- 

 ditions this automatic rhythmical catalysis bears an undeniable and 

 striking resemblance to the action of living tissues like the heart, in 

 which a rhythmical autostimulation is the distinguishing characteristic. 

 In both cases an alteration of a surface- film is the critical change; and 

 the rate of this change determines the rate of the other rhythmical 

 events of the cycle. We may infer that if we could control the condition 

 of the plasma-membranes of cells we could control the entire range of 

 cell-processes. But I do not wish to prejudge these questions; I make 

 the above comparison chiefly in order to suggest possibilities, and to 

 indicate the desirability of devoting more careful study to the surface- 

 films of cells. Investigation of the conditions of their formation, their 

 permeability and their physical and chemical nature is certain to lead 

 to results of far-reaching importance for biology. 



