PACINIAN BODIES, so named after Filippo Pacini, professor of anatomy at Pisa, who discovered them in 1830, and subsequently published two memoirs upon them. They are peculiar minute organs appended to the ner vous system, and present an arrangement alto gether novel and full of interest, though as yet their use is entirely unknown. " The essential structure of these corpuscles appears to be the following. A single tubular or white nervous fibre leaves the fasciculus of which it forms a part, and carrying with it a process of the fibrous neurilemma, advances right into the centre of a series of concentric ovoidal capsules of fibrous membrane, through a channel which perforates thern all, and which has its proper wall, to which every capsule is attached. All the capsules, except from five to twenty of the inner ones, have spaces between them containing a clear watery fluid. These spaces do not communicate with one another or with the channel in which the nerve runs. Each one is distended by its own fluid, and in the natural state is more or less tense, offering flattened (so that its section is oval instead of round), and in particular much paler. The dark border which has distinguished it hitherto now disappears, and if it were not for the trans parency of the contents of the capsules its fur ther course would be untraceable. It is, how ever, when fresh, and with a good light, dis tinctly seen to proceed along the very axis of the central capsule from one end to the other, and finally to be implanted by more or less of a sw-elling (jig. 483) into the further extremity resistance to external pressure. The innermost capsule of all is an elongated nearly cylindrical cavity, somewhat larger at the further end, and always contains a clear fluid,, which distends it and prevents its sides from falling together. The nerve-tube has the ordinary double dark contour as well as every other character of those found in the ordinary cerebro-spinal fibres until its entry into the central capsule. At that point it becomes less bulky, somewhat of this central compartment. The originally dark border of the nerve-tube does not cease with absolute abruptness, but the two lines of the border coalesce in a somewhat sloping manner, and the pale continuation has merely a single bounding line, and that so exceedingly thin as not to allow of being described as an investment distinct from the rest of the fibre.
This line, as Henle and Kolliker have re marked, is more evident when the edge of the flattened fibre is towards the observer than when the flat surface is upwards, in which latter position it is sometimes altogether absent.
Such is the general plan of the structure of these bodies. Their usual length is from 1-20th to 1-10th of an inch, and their stalk is often 1-10th of an inch long. Though•usually oval, they are often more or less elongated and bent on themselves. Sometimes the internal cap sules only are bent, while the outermost are simply oval. In the human subject they are found in large numbers, detached or in clus ters, in the subcutaneous areolar and adipose tissues of the palm and sole, in connection with the cutaneous nerves, as well as more sparingly in the same connection at other parts of the extremities. A few are also met with in the sympathetic plexuses ; and in the cat in par ticular they are usually so abundant in the mesentery and onientum, as instantly to arrest the eye when these parts are spread before it. They are here indeed most favourably situated for examination. They are included merely between the duplicature of the transparent peri toneum, can be obtained in great numbers per fectly fresh, and admit of being inspected with out the addition of any water or other medium.
To the naked eye they here present a beautiful semi-transparent pearly lustre, with a whitish opaline streak along the axis, resulting from the greater proximity and density of the series of intemal capsules. In some animals of this species they have appeared to me almost want ing. It is remarkable that in no instance have they been detected in connection with nerves purely motor, nor, it is affirmed, on the fifth nerve or the glosso-pharyngeal.