262 . ON THE SENSES. 



promptly perceived, no inconsiderable amoitnt of either must be present in order to 

 produce pain. Next, the degree of pain by no means maintains so exact a pro- 

 portion to ihe degree of the excitement ; they do not observe so parallel a 

 course that from the intensity of the pain we can form a certain determination 

 respecting the magnitude of the exciting cause. Finally, the relative duration 

 of the pain and of its cause depends on very different conditions ; the pain often 

 first arises long after the access of the cause which provokes it, and outlasts the 

 latter in many cases for a considerable time, as we need not show by special 

 examples. 



"We hope that this general outline has sufficiently satisfied our readers of 

 the important characteristic differences between the proper perceptions of the 

 sense of touch and of the common feelings produced by the nerves of sensa- 

 tion. We turn now to a closer consideration of the individual action of those 

 nerves, and especially to the operations of the sense of touch. 



As it has been above stated that the sensations of touch, and hence the per- 

 ceptions of pressure, of warmth and of cold, only arise when the corre- 

 sponding irritants act in a moderate degree upon the ends of the nerves in the 

 outer skin and the cavity of the month, the task which next awaits us is to in- 

 quire into the nature of these outer ends, to seek, with the help of the micro- 

 scope, to discover the structure of those terminal points which we regard as or- 

 gans of sense, in order to explain, if possible, the specific action v/hich is only 

 exerted from those outward points. But, alas, respected reader, no satisfactory 

 solution of this important problem has as yet proved practicable to science. 

 With the best microscopes it is extremely difficult, and in many cases wholly 

 impossible, to follow the individual nerve-fibres to their final terminations ; we 

 often see them, after grov,dng extremely thin and pale, disappear among the 

 elements of the tissue into which they enter, without our being able to say 

 what has become of them. Until lately we possessed, regarding the destina- 

 tion of the nerves in the skin, scarcely anything more than conjectures, and of 

 these the two principal -were contradictory. According to the one the nerves 

 terminated in loops — that is, they were bent round under the cuticle, and the 

 fibres thus bent returned again into the nerve stem ; according to the other, the 

 ends in which the fibres terminated were free. Recently, the latter conjecture 

 has been fully confirmed, no less by direct observation than upon physiological 

 groi^^ds, in which the free termination was a priori assumed as a postulate; 

 but the nature of the free extremities and the structural arrangements which we 

 must suppose to be connected Avith them remained, till even a recent day, just 

 as obscure in regard to the skin as to other organs of sense. Within a short 

 time past, however, we are indebted for much light to the investigations of a 

 physiologist of great merit, R. Wagner, and his scholar Meissner. For their 

 better comprehension we must premise that the skin consists of two distinct 

 layers; the outer, superficial cuticle {cpider?nis,) which appears to be only a 

 protective covering, consists of merely flat microscopic plates or scales over- 

 laying and connected with one another. As the exterior layers of this cuticle 

 are constantly wearing away and falling off", they are still repl iced by new 

 layers which form on the under side. The second or proper skin, the cutis 

 {Ixder/iaut,) is a closely interwoven tissue, Avhose substratum is a somewhat soft 

 mass penetrated by numberless small and flexible fibres. In this mass, which 

 gives to the skin its firmness as well as extensibility, a network of fine 

 blood-vessels is imbedded; nerve-stems also enter it in great number and pass 

 with many convolutions towards the upper surface of the cutis, where the sin- 

 gle nerve-fibres become disentangled and terminate close under the cuticle. The 

 surfiice, where the lower skin is bounded by the cuticle, is by no means a smooth 

 or even one, but is beset with countless cone-shaped prominences, which fit, as 

 the fingers do iu a glove, into corresponding cavities of the cuticle. It is into 



