58 



Scientific Proceedings (31). 



E. The fact that an irritable tissue loses irritability for a variable 

 usually brief) period after stimulation (refractory period), — indi- 

 cating that at that time the property of semi-permeability, on which 

 electrical stimulation depends (Nernst), — is temporarily lost. 



The special observations presented in this paper are as follows : 



1. Arenicola larvae are stimulated intensely by pure isotonic 

 solutions of various salts (NaCl, KCl, NH.Cl, LiCl, SrCl2, BaCy, 

 contracting to half their length for several seconds when first in- 

 troduced into the solution. At the same time a yellow pigment 

 contained in the cells of the organism diffuses freely to the exterior 

 and colors the solution. 



2. Solutions which do not produce this strong initial contrac- 

 tion do not cause such loss of pigment. Isotonic CaClj and MgClj 

 (especially the latter) are instances. In these solutions the muscles 

 lose the power of contraction and the organism becomes stiff and 

 motionless (though still propelled by the cilia which remain 

 active). Addition of small quantities of CaCl2 to a NaCl solution 

 prevents the strong initial contraction and loss of pigment 

 (antitoxic action). 



3. MgClj and similarly acting solutions appear to decrease the 

 permeability of the tissues, and so prevent the ionic transfer on 

 which stimulation depends. The general action of anaesthetics 

 consists in decreasing the tiormal permeability ; stimulating agencies, 

 on the other hand, have the reverse effect. 



4. Strong solutions of fat-solvents (chloroform, ether, benzol, 

 (etc.) produce a contraction of the muscles accompanied by loss of 

 pigment, even in w/2 MgCl2. This effect is to be referred to an 

 alteration of the lipoid substances in the plasma membrane. Such 

 alteration, if slight, decreases permeability (anaesthetic action in low 

 concentrations) ; if extreme, it produces the reverse effect, with re- 

 sulting stimulation. 



5. The hypothesis is presented that the chemical effect of the 

 above changes in permeability depends essentially on their influence 

 in varying the rate at which carbon dioxid leaves the cell. The 

 velocity of the oxidative energy-yielding processes whose end- 

 product is CO2 is thus varied with the rate of removal of this latter 

 substance from the system ; this velocity is accordingly increased 

 during the increased permeability of stimulation, and is decreased 



