270 PROTOPLASMIC ACTION AND NERVOUS ACTION 



sensitivity of many blood cells to mechanical contact 

 illustrates the same phenomenon; a slight touch with a 

 capillary needle is often sufficient to cause a rapid and 

 complete disintegration of a leucocyte or a red blood 

 corpuscle;^ i.e., a wave of alteration involving the " 

 breakdown of the semi-permeable surface-film is propa- 

 gated over the entire protoplasmic surface. The break- 

 down of the explosive corpuscles in Crustacea^ and of 

 nematocytes in coelenterates are other examples of the 

 same kind of process. Such facts suggest that in normal 

 cases of stimulation, as in nerve, where a local stimulus 

 initiates a temporary disturbance, which passes like a 

 wave over the entire irritable element, a similar disinte- 

 gration of the surface-protoplasm occurs, with the differ- 

 ence that this change is immediately and rapidly reversed 

 by the formation of a new surface layer. 



That some such process occurs during the transmis- 

 sion of the excitation-wave in a nerve or other irritable 

 tissue is indicated by the character of the local bio- 

 electric variation. A reversible surface-change is 

 known to accompany the transmission of the activation- 

 wave along a passive iron wire immersed in nitric acid; 

 the passivating surface-film is removed by electrolytic 

 reduction in the neighborhood of each active area, and 

 is then immediately reformed by the oxidizing action of 

 the acid and of the local electric current (at the anodal 

 areas); and the destruction and re-formation of the 

 film are associated with definite and rapid variations 

 of potential. In the stimulated living system a similar 



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



2 Cf. Hardy, Journal of Physiology, XIII (1892), 165; Tait, Quarterly 

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



