xii PREFACE 



the truth has, however, been stated, for there is prob- 

 ably no exaggeration in saying that the effects pro- 

 duced by all chemical compounds which act directly 

 on the nervous system are mainly of the same kind. 

 These compounds do not give rise to quantitative 

 changes ; they do not alter the chemical composition 

 of the bodies of which nerve-cells are formed, although 

 they may contribute materials for the purpose of 

 building them up. A little alcohol, we may suppose, 

 has passed from the digestive organs into the blood, 

 and has finally reached a nerve-cell. Its presence 

 undoubtedly modifies the environment of the cell, and 

 influences its molecular movements, its metabolic 

 rhythm, in the same way as the salt or the sulphur 

 does that of the nerve-ending. But if the alcohol be 

 broken up into carbon, hydrogen and oxygen, its 

 specific action must at once disappear. If we were 

 to imagine chemical compounds as acting on the 

 nerve-cells quantitatively, then we should have to 

 conceive the tissue of the cell as being ready to absorb 

 at once, within certain limits, any quantity of carbon, 

 hydrogen, oxygen, or nitrogen which might be offered 

 to it, and one's apparently well-grounded belief in the 

 constancy of the chemical composition of the chief 

 bodies contained in nervous matter would melt away. 

 When, therefore, we have on the one side variability 

 iu the chemical composition of the constituents of the 

 nerve-cell, together with quantitative changes therein, 

 and on the other side constancy in the chemical com- 

 position of these constituents, together with dynamic 



