350 PROTOPLASMIC ACTION AND NERVOUS ACTION 



The ability of living protoplasm to form fresh semi- 

 permeable surface-films at cut or injured surfaces has 

 long been known, and with the introduction of the 

 methods of micro-dissection this property has lately 

 become the subject of renewed investigation.' The 

 rate and other features of the film-forming process vary 

 widely in different forms of protoplasm, and also in the 

 same form of protoplasm under different conditions; 

 thus it is less active in cells that have been subjected to 

 abnormal conditions than in normal and ''healthy" 

 cells. ^ Apparently this process is of the same nature as 

 the reconstructive change occurring at the surface of 

 irritable elements after stimulation and occupying the 

 first part of the relative refractory period. In many 

 respects the refractory period resembles a brief period 

 of fatigue; and it is well known that rapid recovery 

 from fatigue, i.e., a complete restoration of the state 

 preceding stimulation, requires that the supply of oxygen 

 and the other environmental conditions should be normal. 

 In the absence of these conditions excessive stimulation 

 may lead rapidly to the physical disorganization and 

 death of the protoplasm. Some of the effects of extreme 

 fatigue (e.g., development of acid reaction, rapid onset 

 of rigor) resemble those produced by cytolytic agents; 

 and it is possible that certain metabolic products formed 

 during activity have themselves a directly cytolytic 



^ Cf, Chambers, American Journal oj Physiology, XLIII (191 7), i, 

 for a description of film-formation after injury in egg cells. Also Jour. 

 Gen. Physiol., V (1922), 189. 



2 Seifriz {Annals of Botany, CXXXVIII [1921], 269) cites numerous 

 observations on film-formation in protoplasm under various conditions; 

 cf. also his article in Botanical Gazette, LXX (1920), 360. 



