MEMBRANE CHANGES DURING STIMULATION 349 



out the internal protoplasm as well, with the result that 

 the cell breaks down. The rapid disintegrations charac- 

 teristic of the ''explosive" blood corpuscles of Crustacea^ 

 and of the vertebrate platelets, and the phenomena 

 exhibited by other rapidly and irreversibly reacting 

 cells like nematocysts and certain unicellular gland 

 cells, appear to be examples of the same type of process. 

 In all such cases the surface-film is stable only so long 

 as its continuity is uninterrupted; interruption initiates 

 a wave of disintegration which may involve the entire 

 film-structure of the protoplasm. 



In the cellular elements composing typical irritable 

 tissues like muscle and nerve, in which the effects of 

 stimulation are automatically reversed when stimulation 

 ceases, the indications are that an essentially similar 

 process of film-disintegration occurs during stimulation, 

 but with the difference that a new surface-film is immedi- 

 ately re-formed. Whether the effects of stimulation are 

 reversible or irreversible appears to depend on the 

 ability of the protoplasmic system to re-form the structure 

 necessary for stimulation. Under abnormal conditions, 

 e.g., lack of oxygen, presence of depressant poisons, or 

 disease, the rate of metabolic synthesis may be insufficient 

 for complete restoration in the intervals of stimulation, 

 and in such cases excessive stimulation may lead to the 

 death of the cell. But, normally, recovery is rapid and 

 complete in irritable elements of this class; as already 

 pointed out, the indications are that the new film-struc- 

 ture is formed during the earlier part of the relative 

 refractory period. 



I Cf. W. B. Hardy, Journal of Physiology, XIII (1892), 165; Tait, 

 Quarterly Journal of Experimental Physiology, XII (1918), 42. 



