THE MOLECULAR THEORY OF EXCITATION 591 



value when the molecular distortion was proceeding at a 

 rapid rate, and not so much when a condition of permanent 

 distortion had been attained. It is for this reason that, 

 usually speaking, the excitatory effect is most pronounced 

 at either kathode-made or anode-break, 1 and not so much 

 during the continuation of kathodic action. 



To recapitulate some of the principal facts enumerated 

 above, the term * excitatory ' being applied to a particular- 

 directioned distortion or K-effect, then anything which 

 induces an incipient molecular distortion in the same direc- 

 tion, tending to aid the K-effect, and therefore to enhance 

 that response, will be known as K-tonus. Anything, on the 

 other hand, which induces an incipient distortion in the 

 opposite direction, will oppose or retard the normal K-effect, 

 and will, therefore, be known as inducing A-tonus. 



In the examples given, the opposite K- or A-effects 

 observed were the outward manifestations of the aggregate 

 molecular effects induced. And from these we inferred the 

 opposite-directioned changes which must have been their 

 antecedent cause. In working with inorganic substances, 

 however, and particularly in dealing with magnetic bodies, 

 our power of molecular scrutiny is much keener. A rod of 

 iron, for example, is known to consist of magnetic particles, 

 each one of which is a true magnet, possessed of polar 

 properties. Under ordinary circumstances these magnetic 

 molecules are in close chains, but under the action of 

 magnetising forces they become distorted in a directive 

 manner. Under north-magnetising force they are distorted 

 in one direction, and under south polar induction in the 

 reverse. The intensity of the induced magnetisation is a 

 measure of the degree of molecular distortion, and can be 

 gauged by the deflection of the freely suspended needle of a 

 magnetometer in the neighbourhood. Increasing magnetising 

 force is thus seen to induce greater magnetometric deflections, 



1 It is conceivable that there should be occasions in which the final condition 

 of distortion is not attained quickly, but slowly ; or where it is fluctuating instead 

 of stable. Under such circumstances the excitation induced would be more or 

 less persistent or tetanic. 



