314 RALPH S. LILLIE. 



In both cases the same kind of physico-chemical modification 

 in the irritable element appears to form the essential determining 

 condition. 



The phenomena of anaesthesia have thus the widest biological 

 interest; they belong chiefly in the class of chemical inhibitions 

 or desensitizations. The inverse phenomenon of sensitization 

 enhancement of irritability or responsiveness is equally wide- 

 spread and plays an equally important physiological role. 

 Although its study has received less attention than that of 

 anaesthesia, its physiological interest is no less great. Irrita- 

 bility may in fact be altered reversibly either in the direction of 

 increase or decrease. 



It is important to note that the same substance may cause 

 either increase or decrease of irritability or spontaneous activity, 

 according to the conditions of concentration, temperature, physio- 

 logical state of the organism, etc. In the group of lipoid-solvent 

 substances, which include most of the anaesthetics in common 

 use, weak solutions very generally increase excitability; stronger 

 solutions, within a certain range of concentrations, produce 

 typical reversible narcosis; while still stronger solutions cause 

 cytolysis. The basis common to all of these effects requires to 

 be determined. The problem of the general nature of anaesthesia 

 is in fact inseparable from the wider problem of the nature and 

 conditions of irritability in general. The essential question may 

 be expressed thus: what is the physico-chemical basis of this 

 property of irritability, and what conditions determine its rever- 

 sible increase or decrease by chemical or other agents? This 

 problem is one of the most fundamental in biology; and the 

 phenomena of artificial anaesthesia are of general physiological 

 interest largely because of the light which they throw on this 

 larger problem. 



Instances of increase in irritability or spontaneous activity 

 under the influence of low concentrations of anaesthetic sub- 

 stances are frequent in both animals and plants. One of the 

 most familiar is the general nervous excitement caused by small 

 doses of ether, alcohol and other narcotics. Automatic rhythm- 

 ical activity, as of cilia, spermatozoa, or the heart beat, is very 

 generally heightened in weak solutions of alcohol and other 



