2OO RALPH S. LILLIE. 



seen in motile plant organs. The sudden movements of Mimosa 

 leaves, for example, result from a loss of turgor of the pulvinus 

 cells, due to escape of cell-sap a process which, as Sachs ' long 

 ago pointed out, signifies temporary increase in permeability. 

 Since the movement is induced by the same stimuli as cause 

 contractions in muscle-cells, and since it is accompanied by a 

 similar electrical variation or action-current (as Burdon-Sanderson 

 first showed), the inference seems natural that the primary change 

 in the stimulation of animal cells is also a temporary increase in 

 permeability. It remains therefore to inquire how such a change 

 could lead to such seemingly disproportionate liberation of chem- 

 ical and mechanical energy. I have recently discussed the rela- 

 tion of permeability-changes to stimulation in some detail and 

 need not repeat in extmso the facts and arguments presented in 

 these papers. 2 Briefly these are as follows: (i) Artificially-in- 

 duced increase in permeability through the action of various elec- 

 trolytes, lipoid-solvents, or protoplasmic poisons, produces con- 

 traction in muscle cells ; (2) the death change, which is associ- 

 ated with an increase in permeability, produces the same effect ; 

 (3) the electrical change always associated with stimulation is of 

 a kind indicating temporary depolarization of the plasma-mem- 

 brane ; (4) the loss of irritability at the height of stimulation 

 (refractory period) is what should be expected if the plasma- 

 membrane becomes freely permeable to ions at such times ; (5) 

 there are certain inorganic phenomena, showing remarkably close 

 analogies to stimulation, where the effect depends on dissolution of 

 a surface-film (pulsatile mercury and hydrogen peroxide catalysis 

 of Bredig and his pupils) ; finally (6) the chemical effects of stim- 

 ulation increased production of carbon dioxide with increased 

 acidity of the muscle substance, etc. receive a consistent ex- 

 planation on physico-chemical grounds if it is assumed that with 

 the increase in permeability the resistance to the escape of the 

 products of oxidation particularly carbon dioxide and hence 

 also to the progress of the oxidative energy-yielding reaction is 

 suddenly diminished ; the velocity of this reaction hence under- 



'Cf. Sachs' "Lectures on the Physiology of Plants," 1882. English translation 

 by Marshall Ward, Oxford, 1887, p. 653. 



2 American Journal of Physiology, 1908, XXL, p. 2OO ; XXII. , p. 75 ; 1909, 

 XXIV., p. 14. 



