The Internal Senses. 683 



miles, each pair of operators sending and receiving at the same rate of 

 speed as in the ordinary single transmission. It is obvious that musical 

 tones may be perfectly reproduced at any distance b} T this method, and, 

 in fact, this has often been accomplished with remarkable success." (See 

 Johnson's C} r clopedia.) 



There is, to say the least, a striking and powerful analogy between 

 the action of this harmonic telegraph and the organic apparatus which 

 conveys external impressions to our sensorium. In the first place, the 

 senses are each adapted to be set in motion by the impact of some spe- 

 cial vibrator} 1 " agitation ; and in the case of the ear and eye at least, dif- 

 ferent divisions of the organ, viz., the arches of corti in the ear, and 

 the rods and cones in the eye, are adapted to be agitated by different 

 tones of the vibratory stimulation. The organs of ' ' general sensibil- 

 ity " in the skin, are also susceptible to different tones of heat. All 

 these organs correspond to the transmitting instruments of the Har- 

 monic telegraph above described, while the receiving organs in the sen- 

 sorium are analogous to its receiving instrument, and must be conceived 

 as being so tuned as to be susceptible to the influence of its correspond- 

 ing transmitter, and that alone. 



The correspondence of the nerve to the wire as a conductor is equally 

 close and striking, for the nerve bundle, like the wire, will carry all 

 tones of stimulation, and will offer all of them to each of the receiving 

 organs. But only one particular tone of the many conveyed, is compe- 

 tent to set up a normal vibration in any one of the receiving organs of 

 the sensorium, the effect depending on the form and molecular constitu- 

 tion of the receiving organ. 



While it has been shown to be probable that there is a degree of in- 

 sulation in the bundles of nerve fibres by reason of their cases, or neuri- 

 lemma, it is certain this is not absolute or complete, since the neuri- 

 lemma is itself a conductor if the current be -strong enough. But if we 

 consider the exclusive nature of the receiving organs themselves, we 

 perceive that their normal functions are not dependent upon the perfect 

 insulation of their nerve fibres from those of their fellows. The case 

 is parallel to that of the resonators in relation to sounds, explained in 

 chapter 39. No matter how many kinds of vibration assail the resona- 

 tor, it can only be made to respond to one particular tone, viz. , its own 

 fundamental. 



External objects impress themselves upon the brain in two ways ; first, 

 directly, as when they reflect to us .some form of force, as heat, light, con- 

 tact, sound, &c. , second, indirectly, as when we get the impression of an 

 object, not from the object itself, but from something associated or con- 

 nected with it. Thus, words by association of their sound with partic- 

 ular things, awaken the same impression as the original things them- 



