ON THE SENSES, 



1— THE SENSE OF FEELING. 



Trauslated for the Smithsonian Institution from the German periodical, " Aus der Natur, 



u. s. tc.,!' Leipzig. 



The senses, ttose open portals of the soul through which its perception of 

 external things is constantly streaming in ; the sources from which, whether con- 

 sciously or unconsciously, it derives its impulses to thought and action, are, to 

 many even of the educated, possessions so little understood and so wrongly ap- 

 preciated in many important respects, that the attempt to afford a clear insight 

 into their manifold and marvellous sphere of activity can scarcely be otherwise 

 than acceptable. It is not the mechanism of that activity, the structure of the 

 apparatus and the complex and connected series of incidents which occupy the 

 seemingly slight interval between the vibration of a string or flash of a sunbeam, 

 and the well recognized sensations of sound or light, which form the sole prob- 

 lems of such a discussion. The physiologist, with his vast apparatus of knowl- 

 edge and expedients, stands here before a mysterious deep, into whose darkness 

 no hypothesis sheds light, for penetration into whose recesses no accessible path 

 or guiding hand offers itself to his keenest researches. We may wonder at the 

 rapid and brilliant development of modern physiology, even as regards its in- 

 quiries into the theory of sensation, at the dexterity of the microscopist in dis- 

 entangling the structural complexities of the organs of sense, the accuracy with 

 which the path of light has been traced in the camera obscura of the eye, and 

 the form of the vibration communicated by the air- wave to the apparatus of the 

 ear ; but everywhere, in regard to every organ, we come upon an abrupt boundary 

 to our researches — the edge of that enigmatical deep, within which lies hid the 

 true and intrinsic germ of the physiology of sense. What passes in the delicate 

 filament of the optic nerve when a wave of light strikes its extremity in the 

 retina of the eye ? That is the first great problem, whose solution may now, 

 perhaps, have been brought within reach, but which has heretofore lain at an 

 unapproachable distance. We know that it is a motion which, in the fibre of 

 the eye, telegraphs to the brain the arrival of the light-wave ; an ingenious 

 savant has even measured the velocity of that motion, but the moving force, the 

 matter moved, and the form of the movement, are as yet unknown. But were 

 even this problem solved, did the mechanism of the organs and the processes in 

 the nervous fibres, which convey the impressions of the outer world to the soul, 

 lie before us in noonday clearness, there would yet remain for us the last and 

 most difficult problem : How does this physical motion, Avhich shoots along the 

 nerve-filaments, become in the brain a conscious sensation ? Sensation and 

 current (since thus we must express ourselves) are in the nervous fibre two 

 wholly different and in nowise comparable things — just as much so as the de- 

 spatch of the telegraph and the electric stream which traverses the wires ; we 

 know that the sensation is produced and its conditions determined by the 

 current, but the nature of the causative connexion is to us a mystery, like that 

 of the sensation itself. These passing intimations, which will assume in the 

 course of our inquiries a more definite and intelligible form, are here premised 



