184 THE INTELLIGENCE SERVICE 



states that there is no evidence to show that the nerve impulse 

 is in any way modified by the nature of the stimulation. Each 

 nerve has however a rhythm of its own an optimal rate of 

 stimulation known as Waller's " characteristic," which is similar 

 to the natural rate of incidence of energy. 



No difficulty should be experienced in grasping this idea. 

 especially if an electrical model be kept in mind. 



Consider an electrical circuit such as shown in Fig. 33B. C is 

 a galvanic cell or electrical unit where chemical energy is converted 

 into electrical energy. F l and F 2 are wires connecting C to 717. an 

 electric machine, and a key closes the circuit, (a) It does not 

 matter how the key is closed, the current passing along F will be 

 the same, and (b) the manifestation of the current will depend 



NERVE CELL 



DENDRITE5 IN 



A 



DENDRITES IN 



ff CONDUCTING AAON RECEIVING AXON 



MOTOR ORGAN V RECEPTOR OR^N 



GALVANIC CELL 



]'[;. :!:!. \. Diagram of a unit of the nervous system compare,! with 15. 

 15. Kleetrical Model to illustrate .Miiller's Law and the "All or Nothing" hypothecs 

 as explained in the text. 



on the nature of M. If M is a telephone receiver, the closing 

 of the key will cause a sound to be heard, if M is an incandescent 

 globe, light will be seen, if M is a motor, motion will result, and 

 so on. The electrical energy of C can thus be converted into any 

 form of energy by an appropriate M. Further, the magnitude 

 of the force applied to the key makes no difference to the 

 magnitude of the resulting manifestation at M. That depends on 

 the energy set free by the cell and on the resistance of the circuit. 

 Of course the receptor must be modified to suit different kinds 

 of stimuli. A telegraph key or a bell push is a convenient kind of 

 mechanism for closing a circuit mechanically, but it would not 

 answer for electrical, thermal, sound or light vibrations. Special 

 means for closing the circuit have to be devised to suit different 

 kinds of stimuli. For example, sound waves may be caused to 

 close an electrical circuit by microphone, e.g. telephone trans- 

 mitter. 



