348 PROTOPLASMIC ACTION AND NERVOUS ACTION 



sufficiently strong to excite other irritable tissues. 

 Hence the local production of such a current within the 

 irritable element itself might be expected to cause 

 stimulation in adjoining area^ of the same element, 

 an effect which would be repeated at the boundary of 

 each area thus secondarily stimulated, and thus form 

 the condition for a spread of excitation, in the manner 

 already indicated. 



There is, in fact, a large body of evidence indicating 

 that any rapid local increase of permeability, however 

 induced, acts as excitant to an irritable cell or element. 

 Mechanical treatment, like pricking or sudden pressure, 

 the sudden application of heat, and rapidly acting 

 cytolytic agents all have a stimulating effect on muscle 

 or nerve. It is interesting to note that many cells, not 

 ordinarily classed as irritable, undergo rapid and spon- 

 taneous structural alteration or breakdown under condi- 

 tions involving local increase of permeability. This is 

 well seen in the effects following the puncture with 

 capillary needles of the surface of red blood corpuscles 

 and other cells; frequently a disintegration starts at 

 the point of injury and rapidly leads to the breakdown 

 of the entire cell.^ In a red corpuscle thus treated the 

 exit of haemoglobin may be seen to begin simultaneously 

 over the whole surface.^ It is clear that in such cases 

 the surface-film undergoes a sudden and irreversible 

 increase of permeability; this change is propagated over 

 the whole surface, and apparently in many cases through- 



^ Cf . Kite, American Journal of Physiol., XXXII (1913), 146; 

 Chambers, Science, XL (1914), 824; XLI (1915), 290; Oliver, Science, 

 XL (1914), 645. 



2 Cf. Chambers, Anatomical Record, X (19 16), 190. 



