There is little to add to the description of the nerve-tube already given. It is faintly granular in texture, and occasionally regains, at one or more points of its course within the central capsule, the dark contour which it had lost on entering it. This is particularly the case vvhen it follows a bend of the cavity, and certainly seems to indicate the presence there of a material elsewhere deficient. It is rare, how ever, to see this re-assumption of the dark border in any very well-marked degree. The mode of attachment of the end of the nerve fibre varies, being generally by a single tubercle or conical swelling, sometimes by two, and sometimes even by three such. Whatever the number of bmnches, however, their aggregate thickness is about the same as that of the simple fibre from which they spring. Where the cen tral cavity exhibits the offsets above-mentioned the pale nerve-fihre is also invariably branched, its subordinate branch always traversing the axis of the subordinate cavity, and being regu larly fixed at its extremity. It is interesting to observe how accurately the nerve-fibre preserves its place in the axis of the central cavity, how ever abruptly that may be bent or branched, a fact which might be supposed to indicate some degree of viscidity in the clear substance through which it runs.
Respecting the function or use of the Paci nian corpuscles no satisfactory account has yet been given, nor even a plausible explanation offered. Their presence in so great abundance on the nerves of the palm and sole, and their absence from motor nerves, suggests the ob vious enquiry, whether they may not be con nected in some way with the sense of touch, or at least with the function of sensation, to which the fact of their concentration in such numbers in the splanchnic nerves of some animals as obviously answers in the negative. Undoubt edly, however, we may anticipate much from a more extended research into their connections with the several parts of the nervous system in man and animals, than the very recent date of their disvovery has yet allowed. The specu lation that they may be concerned in the pheno mena of vvhat is called animal magnetism is not to be passed over with contempt, if only because it has been hazarded by their distin guished discoverer, Pacini, who, in common with many other unprejudiced and not inca pable observers, is inclined to believe in the reality of some of the less marvellous effects which popularly pass under that title, such, in particular, as the mesmeric somnolence and catalepsy. Yet so vague an hypothesis, per haps, barely deserves to be placed in juxta position with the descriptive anatomy of the corpuscles.
It will be more to the purpose to institute a brief comparison between these bodies and the electrical organs of the torpedo, a description of which will be found under the head of ANIMAL ELECTIIICITY. Since that article MS written, however, further researches, and especially those of Savi,* have added some points of im portance which it will first be necessary to no tice. Tile prisms of the electrical organ, as Ilunter described, are divided by very nume rous horizontal diaphragms into spaces con taining a thin fluid, and on these diaphragms the nerves and vessels of the organ are ulti mately distributed in great abundance. Each of these superposed diaphragms consists of a layer, possibly double, in and not upon which the nerves ramify. The nerves of the electrical organ have never any ganglia formed upon them. Their tubules always have the double
contour which marks the presence of the white substance of Schwann. The ramifications pe netrate between the prisms, and each diaphragm receives tubular fibres at several points of its circumference, though Savi is doubtful whether these are derived from two or more tubules of the branch supplying then). In the diaphragm, however, they are uniformly spread out in a network with five or six-sided meshes, the sides of which are everywhere formed by a single tubule with double contour of the same diameter and structure as the tubules of the trunk of the nerve. If this network is supplied from several different tubules, these tubules must be described as inosculating to form it; if from a single tubule, this must be regarded as ag-ain and again branching dichotomously, and the branches repeatedly anastomosing. NI'hichever be correct, the existence of a true network of ultimate nerve-tubes with double contour is certainly a fact of much importance, and hitherto unique ; and it appears to be satisfactorily established by the repeated accu rate observations of Savi.
The series of superposed membranes in the prisms of the electrical organs may have an analogy with the concentric capsules of the Pacinian bodies. Their separation by inter vening fluid is another point of resemblance. But in their relation to the nerves they are quite unlike. In the one, eadi membrane has a plane network of nervous tubules in its sub stance ; in the other a single nerve-fibre is placed in the axis of a series of concentric membranes. The condition of the nerves is also different. In the one the white substance of Schwann everywhere invests the nerve ; in the other it is suddenly lost on entering the central capsule. The branching of the nerve tubes in the electrical organ has a correspon dence with the frequent tendency of the pale fibre of the Pacinian corpuscle to divide into two or more parts. On the whole, perhapi, the comparison may suffice to raise the ques tion, whether the Pacinian corpuscles may not be organs designed to generate some kind of force, which the nervous communication with the centres may serve to connect either with volition or some emotional impulse or feeling.* There is another set of organs, however, in the electric torpedo, the discovery of which we owe to Savi, and which bear a closer resem blance to the Pacinian corpuscles than the electric organs themselves. 1 hese are what he terms the follicular nervous apparatus, and which I shall briefly describe nearly in his own words.* " This apparatus is found bordering the an terior part of' the mouth and nostrils, and ex tends over the surface of the anterior part of the electrical organs, and over the front half of their outer edge, where it rests upon the carti lage and aponeurotic coverings of the fin. Some parts of the apparatus are found on the back, but the greater portion on the ventral surface of the animal. It consists of extensive linear series of follicles, or closed membranous cells with double walls filled with a gelatinous fluid, and enclosing a small amorphous granular mass, which nearly resembles the amorphous grey matter of the cerebral hemispheres. A nervous branch gives some fibres to this granu lar mass, while other similar fibres united into bundles pass out of the follicle, penetrate the grey mass of the adjoining follicle, and mingle with its nerve.