260 



SCIENCE 



[N. S. Vol. L. No. 1289 



plete and rapid dissolution as a result of slight 

 local mechanical and chemical alteration; any 

 interruption of continuity sets up a local cir- 

 cuit and initiates a process of dissolution 

 which may be propagated over the whole sur- 

 face and result in the complete destruction of 

 the film; many living cells (e. g., blood cor- 

 puscles) are thus imstable, as is also the 

 passive state of a metal like iron in most 

 solutions. Accordingly, vmless the film is 

 automatically restored whenever it is inter- 

 rupted, the state of passivity in a metal, such 

 as iron, or of continued life in a living cell, is 

 temporary and never lasts long. A special 

 peculiarity of such systems, however, is that 

 when the passive metal is immersed in a suit- 

 able oxidizing solution, or the living cell in its 

 normal medium, the continuity of the film is 

 preserved by an automatic regulatory process 

 of the type just indicated; and under such 

 conditions the passive or the living condition 

 may be a highly stable one. Automatic re- 

 version to the passive or resting condition is 

 in fact the rule in metals or in irritable ele- 

 ments under certain conditions. This pecu- 

 liarity is an especially important one from the 

 physiological standpoint, and its basis will be 

 further considered below. 



If, as the local action theory of stimulation 

 would imply, the control of protoplasmic pro- 

 cesses is largely dependent upon the peculiar 

 properties and behavior of surface-films of 

 this type, it is clear that the general physics 

 and chemistry of such films must be a matter 

 of fundamental interest for general physiol- 

 ogy. Although the films formed upon metallic 

 surfaces are obviously widely different in their 

 chemical composition from those enclosing 

 irritable living elements like muscle-cells or 

 nerve-fibers, they nevertheless exhibit in their 

 general physical properties, conditions of for- 

 mation and behavior many close resemblances 

 to the latter. Ajid it is just those properties 

 which both types of film possess in common 

 that determine the most characteristic fea- 

 tures of their behavior, in particular their 

 " irritability " and their jwwer of transmitting 

 chemical influence to a distance. These are 

 the properties which are of most general phys- 

 iological interest, and they are dependent 



upon simple conditions of a general kind, 

 which are in no way peciiliar to living proto- 

 plasm but are present in varying degree at all 

 boundary-surfaces across which the transfer 

 of electricity in association with chemical 

 change (electrolysis) can take place. 



The surface-film of passive iron is especially 

 suitable for study from the above point of 

 view because of the readiness with which it is 

 formed and its marked sensitivity to mechan- 

 ical and electrical influences; in these and 

 other respects it exhibits a behavior closely 

 analogous to that of the protoplasmic surface- 

 films of irritable cells and cell-elements. The 

 experiments about to be described have aimed 

 at determining the degree to which these 

 analogies extend to other peculiarities of be- 

 havior, and in particular whether definite cor- 

 respondences exist in regard to the influence 

 of electrolytes and surface-active organic com- 

 pounds upon the stability and other properties 

 of the film. Both of these classes of com- 

 pounds have a well-known and characteristic 

 influence on protoplasmic irritability, a prop- 

 erty which is undoubtedly dependent upon the 

 state of the surface-films or plasma-mem- 

 branes of the irritable elements. 



Self-conserving Properties of the Film. — An 

 automatic power of repair is a highly char- 

 acteristic property of protoplasmic surface- 

 films; slight wounds or interruptions of the 

 cell-surface are repaired; more extensive in- 

 jury frequently leads to a rapid breakdown of 

 the entire cell. The normal return of a living 

 irritable element to the resting state after 

 stimulation, or cell-division, or other change 

 associated with alteration of the plasma-mem- 

 brane, appears to depend mainly upon this 

 ability to reform the surface-film. In irritable 

 tissues (muscle, nerve) the time required for 

 this restorative process apparently corresponds 

 with the temporarily insensitive or " refrac- 

 tory " period immediately following excitation, 

 whose duration (as is well known to physiol- 

 ogists) is in general briefer the more rapid 

 the response of the tissue to excitation. Rapid 

 response and rapid recovery are thus con- 

 stantly associated properties of an irritable 

 tissue. A similar automatic restoration of 

 the passivating surface-film after activation 



