128 J. F. MCCLENDON. 



propagation 1 is much slower than the similar process in muscle 

 or nerve. 2 



Pfeffer 3 supposed that the plasma membrane is normally per- 

 meable to ions of only one sign. Since the normal cell surface 

 is positive in relation to the cell interior (cut surface) we may 

 conclude that the plasma membrane is normally more permeable 

 to kations (less permeable to anions). Just as the negative 

 variation of wounding is due to the removal or rupture of the 

 plasma membrane, so the negative variation of stimulation would, 

 on the membrane hypothesis, be due to increase in permeability 

 of the plasma membrane to the confined anions. 



An alternative hypothesis is that these electrical changes 

 result from changes in metabolic activity. The production of an 

 electrolyte whose anion and kation have very different speeds 

 of migration (such as an acid or alkali) would cause electrical 

 changes. But how are we to account for changes in metabolic 

 activity? There exists varied evidence for changes in perme- 

 ability, and it is simpler to assume that changes in metabolic 

 activity and electrical changes are both the result of changes in 

 permeability. 



Kunkel 4 tried to explain the vital electrical phenomena as the 

 result of the movement of fluids in the vessels of the tissues, but 

 bio-electrical changes may occur without such movement of 

 fluids (Burdon-Sanderson). 



Kunkel observed in i882 5 that the movement of the leaf of 



i 



Mimosa pudica is accompanied by an "action current," or nega- 

 tive variation of one surface of the pulvinus. Similar results on 

 Dioruza leaves were obtained by Munk' 1 and specially studied 

 by Burdon-Sanderson. 7 It was stated above that Lepeschkin 

 had shown that the turgor changes in plants were accompanied 

 or i in mediately preceded by changes in permeability to certain 

 substances. The electrical phenomena suggest that the turgor 



1 Which is in mimosa 600-1,000 times as fast as the geotropic impulse in a root. 



2 Fitting, "Ashcr and Spiro's Ergeb. d. Physiol.," 1906, V., 155. 

 " Pflanzenphyaiologie." 



*Arch.f. iL ges. Physiol., 1881, XXV., 342. 



s See Wintcrstein's "Ilandbuch der vcrgleichenden Physiologic," III. (2), 2, 

 p. 214. 



Arch. f. Anal. it. Physiol., 1876, XXX., 167. 



" Proc. Roy. Soc. London, 1877, XXV., 441; Philos. Trans., 1888, < I XXIX.. 417- 



