324 RALPH S. LILLIE. 



anaesthesia may result from a slight change in this reaction. In 

 higher vertebrates the normal reaction of the blood plasma is 

 not far from neutral, and varies only slightly from a constant 

 normal value (C H ;= 0.35 X io~ 7 to 0.5 X io~ 7 ); but certain 

 cells of the central nervous system are especially sensitive to 

 such variations. The activity of the respiratory center is ap- 

 parently regulated by the variations in the H-ion concentration 

 of the blood, cessation of activity resulting from a slight decrease 

 (i. 6., increased alkalinity), and increased activity from a slight 

 increase. 1 Reversible cessation of activity may thus result from 

 a slight change in reaction, due, e. g., to loss of CO 2 . Similar 

 conditions are known to exist in certain marine animals; thus 

 according to Bethe, 2 slight increase in the alkalinity of the sea 

 water arrests, while slight acidulation accelerates, the rhythmical 

 contraction of medusae. On the other hand, the activity of 

 many cells and tissues is favored by slight increase in external 

 alkalinity, and depressed by slight acidulation. The irritability 

 and automaticity of living cells are thus largely a function of the 

 reaction of the medium, and this fact has an intimate bearing on 

 the question of the mechanism of anaesthetic and other inhibi- 

 tions. The precise physico-chemical basis of this action is un- 

 certain, but it probably depends chiefly on alterations in the 

 electrical polarization of the cell-surface. Slight variations in 

 alkalinity or acidity are known to produce marked effects on 

 the electrical polarization of surfaces bathed by media of approxi- 

 mately neutral reaction. 3 



The chief chemical substances exerting a reversible depressant 

 influence on a wide range of vital activities are those numerous 

 and chemically diverse organic compounds of which the most 

 evident common property is a solvent action on, or solubility 

 in, fats and fat-solvents. Substances of this class form the 

 majority of anaesthetics in common use; they include alcohols, 

 ethers, esters, aldehydes, ketones, nitrites, amides, various normal 

 and substituted hydrocarbons (chloroform, benzol, etc.) and 

 other related compounds. Most of these bodies are members of 



1 For a recent review and discussion of the evidence cf. Winterstein, Biochem. 

 Zeitschr., 1915, Vol. 70, p. 45. 



2 Pfliiger's Archiv, 1909, Vol. 127, p. 219. 



3 Cf. Haher and Klemensiewicz, Zeilschr.f. physik. Chemie, 1909, Vol. 67, p. 385. 



