THE THEORY OF ANESTHESIA. 357 



solution in a closely parallel manner; solutions with relatively 

 high Mg-content cause slight stimulation and slight loss of 

 pigment, while in those of relatively high K-content both effects 

 are well marked. 



Entirely different effects from those of pure solutions of 

 potassium and sodium salts are produced by pure solutions of 

 magnesium salts. These exert typical anaesthetic action on 

 Arenicola larvae, as on other marine animals. When brought 

 suddenly into pure isotonic MgCl 2 solution the larvae show no 

 contraction or loss of pigment; all muscular contraction imme- 

 diately ceases, the body remains rigid and extended; the cilia 

 are more resistant and remain active, and slow undirected 

 swimming movements continue. On return to sea water muscu- 

 lar movement and other normal activities are at once restored. 

 If larvae are brought into isotonic MgCl 2 solution for a few 

 minutes, and are then transferred into pure NaCl solution, the 

 characteristic effects following transfer to the solution from sea 

 water stimulation and loss of pigment are no longer seen ; the 

 organisms remain motionless and without apparent change. 

 If they are then returned to sea water they show prompt revival. 

 Apparently the treatment with MgCl 2 renders the plasma- 

 membrane more resistant than normally to the permeability- 

 increasing action of the pure NaCl solution, and at the same time 

 the muscle-cells become refractory to stimulation. The following 

 was the general conclusion drawn at the time from these facts: 

 "MgCl 2 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 normal permeability ; stimulating agencies 

 on the other hand have the reverse effect." 1 Later experiments 

 with a variety of lipoid-solvent anaesthetics alcohols, esters, 

 ether, hydrocarbons gave essentially similar results; 2 solutions 

 of anaesthetics in pure NaCl solution, in every case where they 

 prevented the stimulating action of the solution, also prevented 

 the permeability-increasing action as indicated by loss of pig- 

 ment; when they did not prevent this effect, they did not 

 prevent stimulation. A general parallelism between prevention 



1 Loc. cit., p. 44. 



2 Amer. Journ. Physiol., 1912, Vol. 29, p. 372; 1913, Vol. 31, p. 255. 



