THE SENSE OF FEELIXG. 253 



In orcler to render clear the distinction between the sense of touch and com- 

 mon feeling, we are forced to take a somewhat wider view. Few of my readers, 

 perhaps, have a correct idea of a nerve and its functions ; and many, who rightly 

 or wrongly impute every evil to the poor nerves, know as little how to justify 

 the charge, as to appreciate ihe services of these scape-goats of the bodily 

 machine. Honestly speaking, physiology itself can aflPord us no certain expla- 

 nation of the nevous energy ; it has a prudent distrust, however, and has chased 

 from the temple many a time -honored error and empty phrase respecting the 

 action of the nerves ; and the elimination of error, we know, is the first step 

 towards the knowledge of truth. 



I assume that my readers have derived from other sources some knowledge of 

 the nature, causes^ and operations of the electric current. Few will be ignorant 

 that such a current, however generated, may be conducted through a naetallic 

 wire, and, according to the nature of the apparatus with which that wire is con- 

 nected, produce the most surprising and varied effects ; that we may thus explode 

 powder, drive the wheels of a car, and set in motion the machinery of a clock or 

 a telegraph. Now, the inunmerable nerve-filamimts which traverse our bodies 

 in all directions are similar to that metallic wire, and the unknown element of 

 activity which shoots along the nerves is analogous to the electric current which 

 flashes along the wire. We wish it to be observed, that we use the word analo- 

 gous as implying that it is by no means the electric current itself which circu- 

 lates in the nerves as in the conducting wires when in a state of activity. Long 

 and persistent efforts have been made in the province of physiology to identify 

 the active principle of the nerves with the electric current on account of some 

 superficial resemblance in the phenomena ; but more recent and exact inquiry 

 has conclusively repudiated this hypothesis, by which the nervous fibres were 

 consigned to the simple office of conductors, and might, it would seem, have been 

 replaced by metallic wires. But though the nervous and the electrical currents 

 are not identical, they are yet strikingly comparable with one another, and we 

 know no better images by which, for general readers, the functions of the nerves 

 can be made intelligible. For, as the electric stream can be produced in the 

 conducting wire by different means and apparatus, so the process in the nerves 

 which we call " a nervous current" can, in various ways, be excited ; if, for in- 

 stance, we lay a nerve bare in a living animal, that nerve is thrown into a state 

 of activity ; or, in other words, the current is produced by wounding or by pres- 

 sure, by an electrical shock or the application of any irritating or corrosive 

 substance. The agent by which such an effect is produced we call an irritant, 

 and this, according to its nature, may be either mechanical, electrical, thermal, 

 or chemical. But besides these irritants which excite the nerves by their direct 

 action, there are a number of others, and those among the most important, v/hich 

 are only competent to that effect under certain circumstances, and with the help 

 of an appropriate apparatus. In this class light and sound are the most promi- 

 nent. We can easily satisfy ourselves by experiments brought to bear upon 

 the exposed nerve of a leg for instance ; neither of those active principles pro- 

 duces the slightest excitement. Lay bare even the optic nerve, and allow the 

 sun to shine upon its fibres, no irritation will be manifested ; but how different 

 the effect when light is admitted to that living and wonderfully constructed ap- 

 paratus by which the ends of those fibres are connected with the pupil of the 

 eye. Analogous effects are witnessed with regard to sound, which then only is 

 operative as a nervous irritant when its undulations have reached the extremities 

 of the auditory nerves after having passed through the exterior mechanism of 

 the ear and the fluid of the labyrinth. The undulations of light and sound, 

 therefore, are only mediate or indirect irritants of the nerves, and excite the 

 latter by means of a peculiar intermediate apparatus, in which most probably 

 they produce some action, whether chemical or physical, by which the nervous 

 current is set in motion. We might presume, for example, that the waves of 



