356 RALPH S. LILLIE. 



plasma-membrane, and a consequent change in the properties 

 of this structure. The temporary increase of permeability, 

 which according to Bernstein's theory of the bioelectric varia- 

 tions, forms an essential part of the stimulation-process, is thus 

 rendered difficult or impossible. 



Very clear and concrete indication that the stimulation of 

 muscle is in fact associated with a temporary increase in the 

 permeability of the plasma-membrane, and that anaesthetics act 

 by preventing this increase, w T as afforded by my own experiments 

 on the larvae of the marine annelid Arenicola, carried out at 

 Woods Hole in IQOS. 1 This larva is a free-swimming trochophore 

 one third of a millimeter long, possessing a well-developed 

 musculature and swimming by cilia, and is peculiar in having its 

 body-cells permeated by a brown water-soluble pigment. This 

 pigment normally remains w r ithin the cells, but under conditions 

 of increased permeability, as on death or under the influence of 

 cytolytic substances, it diffuses readily into the sea-water and 

 imparts a yellow tinge to the latter. It serves therefore as a 

 convenient indicator of increase of permeability. If larvae are 

 brought suddenly from sea water into a pure isotonic solution of 

 a sodium salt (e. g., o.6m NaCl), a strong muscular contraction at 

 once results, accompanied by a well-marked loss of pigment; 

 at the same time the cilia cease movement and soon afterwards 

 undergo breakdown, and other toxic effects follow. If, instead 

 of a pure solution of NaCl, a solution containing a little CaCl 2 

 or MgCl 2 is used, both changes are simultaneously prevented; 

 neither contraction nor loss of pigment is shown ; the cilia remain 

 active, and normal swimming movements continue for a time; 

 the general toxic action of the pure salt solution is also prevented. 

 Thus the calcium prevents at the same time both the stimulating 

 and the permeability-increasing action of the sodium salt. It also 

 greatly diminishes the injurious action of the latter, i. e., exerts 

 anti-toxic action. Pure solutions of KC1 also cause strong mus- 

 cular contractions accompanied by loss of pigment; and the 

 effect is similarly checked by the addition of MgCl 2 . In mixtures 

 of KC1 and MgCl 2 both effects vary with the Mg-content of the 



1 Cf. Amer. Journ. Physiol., 1909, Vol. 24, p. 14. Cf. also ibid., 1911, Vol. 28, 

 pp. 210 seq. 



