THE THEORY OF ANESTHESIA. 323 



especially of the surface-layer or plasma-membrane, is a chief 

 factor in determining the irritability and automatic activity of 

 the living cell. Further evidence of this will be given later. 

 Modification of the properties of this layer may result from an 

 alteration in the state of either its lipoid or its protein con- 

 stituents, and if this alteration is reversible a temporary inhibi- 

 tion, or anaesthesia, may result. A related condition is seen in 

 the irritable tissues of higher animals, such as muscle and nerve. 

 In these tissues irritability depends on the presence of certain 

 salts in the media; simple withdrawal of salts and replacement 

 by indifferent non-electrolytes like sugar is followed by a tem- 

 porary loss of irritability; the latter is restored by return to 

 media containing salts, especially sodium salts. 1 The muscula- 

 ture of marine animals (e. g., Arenicola larvae) is similarly in- 

 activated in isotonic solutions of non-electrolytes, and regains 

 irritability in isotonic solutions of various neutral salts. Solu- 

 tions of sodium salts, together with a small proportion of calcium, 

 are especially favorable. Sodium may be partly replaced by 

 lithium, but not by other metals. 2 Thus the presence of certain 

 salts in the medium is necessary for normal irritability, hence 

 the effects of isotonic sugar solution, which are due to the absence 

 of salts, not to any special action of the non-electrolyte. The 

 salt-content of the medium may be reduced to a small fraction- 

 one tenth or less of the normal by diluting the physiological 

 salt solution with isotonic sugar solution, without causing loss 

 of irritability. But with the complete withdrawal of salts 

 irritability soon disappears. In cases like this, where normal 

 irritability is dependent on the salt-content of the media, modifica- 

 tion of the latter may induce a reversible desensitization closely 

 resembling anaesthesia. Probably several factors enter in the 

 production of this effect, of which the two chief are, a direct 

 change in the properties of the plasma-membrane (colloidal con- 

 sistency, electrical polarization), and a lowering of the electrical 

 conductivity of the medium. 



The reaction of the medium (H-ion concentration) also has 

 profound influence on the irritability and automatic activity 

 of many cells; and a reversible suspension of function akin to 



1 Cf. Overton, P finger's Archiv, 1902, Vol. 92, p. 346, and 1904, Vol. 105, p. 176. 



2 R. S. Lillie, Amer. Journ. Physiol., 1909, Vol. 24, p. 459. 



