592 COMPARATIVE ELECTRO-PHYSIOLOGY 



and on the cessation of the inducing force there is usually a 

 molecular recovery, with a concomitant return of the magneto- 

 metric indicator to its original position. 



Here, then, we have a means of recording the molecular 

 distortions induced in a substance under a given external 

 force. We are able also to study the relation between the 

 acting force and the distortion induced, while it is increased 

 or diminished in a known manner. And further, keeping 

 the acting force the same, we are here able to study the 

 effects of various modifying agents on the response, as 

 recorded by the magnetometer. 



In all these cases, then, we have a strict parallel to the 

 excitatory molecular changes and their variations induced in 

 a living tissue under stimulus. But besides this local action 

 we have also, in the living tissue, nerves possessing the 

 property of transmitting the state of excitation that is to 

 say, the molecular disturbance to a distance ; and this trans- 

 mission is modified appropriately by the various modifica- 

 tions which may be induced in the conducting nerve. Simi- 

 larly I shall be able to show that, in an iron wire, excitatory 

 magnetic disturbance is propagated to a distance ; this con- 

 duction likewise being modifiable by the molecular changes 

 induced in the conducting wire. 



Thus, in those particular cases where molecular scrutiny 

 is possible, we are enabled to visualise with considerable 

 accuracy those molecular events on which excitation and its 

 transmission depend. Afterwards, discarding this illustrative 

 class of magnetic substances, I shall refer to other methods, 

 by which the responsive manifestations of ordinary substances 

 under stimulus, and the modifications of these responses 

 under various conditions, will be recorded. From so compre- 

 hensive a study we shall find that whatever be the mode oi 

 record, and whatever the experimental substance employed, 

 the fundamental reaction, and its variations under particular 

 conditions, are curiously similar. It will then be realised 

 that the response of living tissues is not alone of its own 

 kind, but falls under a wide generalisation. 



