If, then, the fibres of Remak be kept out of consideration, as not being possessed of the properties of nerve-fibres, are there any fibres in the sympathetic which can be regarded as differing in their anatomical constitution from those occurring in the nerves belonging to the cerebro-spinal system ? In 18-12 Bidder and Volkmann described particularly the distinc tion in point of structure between the tubular fibres, which have been mentioned as being present in the syinpathetic. They measured the tubular fibres, and found that while some of them had a diameter of 0-00046 to 0-00068 of an inch, others measured only 0-00012 to 0-00022; and between the two sizes they observed no fibres of intermediate breadth. They also measured the branches which enter and those which leave the ganglia in the frog. The latter were found to exceed the former in point of thickness, which could only be at tributed to the addition of structures arising in the ganglia, and on examination they ob served that the increase in thickness of the one over the other was due to the presence of a greater number of tubular nerve-fibres belonging to the finer variety ; and hence it was concluded that these are the peculiar organic or sympathetic fibre. The coarser variety they regarded as arising in the cerebro spinal centres, while the fibres belonging to the finer variety always, according to them, take their origin in the ganglionic system. They describe these fibres as being about half the diameter of those belonging to the cerebro spinal nerves ; they are further distinguished by their paleness ; the absence, under all cir cumstances, of the double contour, and the small quantity of curdlike contents which they present even when examined some time after death, and by their yellowish-gray colour when in bundles. The distinctions between the broad and fine tubular fibres, as given by Volkmann and Bidder, were denied by Valen tin, who stated that the fibres of these au thors were merely fibres of Remak. Reichert, on the other hand, confirmed the observations of Bidder and Volkrnann as to the difference in point of size and structure between the cerebro-spinal nerve-fibres and the sympathetic or organic fibres. The description which is given by Remak of the gelatinous fibre does not, as Volkmann and Bidder maintain, apply to the fibres which they. have described : they are much finer, ten times finer, than the cerebro-spinal fibres, whereas the fibres of Bidder and Volkmann are generally only a half narrower than these fibres. The relations of the two structures towards reagents as well as their general characters are also very dif ferent Milker agrees with Bidder and Volkmann that there are nerve fibres in the sympathetic which are not derived from the cerebro-spinal system, but arise from the ganglionic cor puscles; he farther confirms the observation of these authors, that all the fibres which arise in the sympathetic belong to the finer variety of tubular fibres, and that they present the characters which they were described by Bidder and Volkmann as possessing ; he de nies, however, that they are peculiar to the sympathetic system. Fine fibres ag,reeing with these in structure arise, according to him, in the cerebro-spinal system, as well as in the sympathetic. Again, the diameter of the coarser and finer varieties of the tubular nerve fibres is by no means so strictly limited as Bidder and Volkmann believed, there being transitions from the finer to the broader or coarser variety. Besides occurring in the sym pathetic, they are likewise present in the anterior and posterior roots of the spinal nerves, especially in the latter; and in the brain and spinal cord they exist in large num bers. Another objection to the views of Bidder and Volkmann as to the peculiar na ture of these fibres is derived from the fact that it is by no means uncommon for the broader tubular fibres to divide into finer fibres during their course to the periphery, becoming narrower and narrower, and at the same time losing their distinct double contour; and hence in their ultimate distribution they consibt almost entirely of fine fibres, which cannot be distinguished from those described by Bidder and Volkmann as constituting the peculiar fibres of the sympathetic system. Volkmann himself now admits that the dis tinction between the broad or animal nerve fibre and the fine or organic is by no means always strictly defined, and also that the broad tubular or animal fibres, in their peri pherical distribution, assume the characters of the others. It would appear, then, as Kill liker maintains, that there is no absolute dis tinction between the fibres of the sy mpathetic and those belonging to the cerebro-spinal system ; the difference is merely one of rela tion and degree : while the nerves of the latter system consist chiefly of broad tubular fibres, the sympathetic is chiefly composed of fine ones.
Ganglia. — The ganglia occurring on the sympathetic are, as has been already stated, very numerous, constituting the most distin guishing character of this nerve. There are also ganglia present on the posterior roots of all the spinal nerves, as well as on several of the cerebral nerves ; and by many these are classified along with those of the sympathetic, constituting what has been termed the gan glionic system of nerves. The ganglia present the appearance of nodules or swellings oc curring on a nerve during its course. When examined with the naked eye, they appear to consist of opaque and more or less pellucid portions, present a greyish colour, and are possessed of considerable consistence. Some
times they occur in the course of a single nerve, as is the case with the ganglia in the posterior roots of the spinal nerves. The sympathetic ganglia commonly present the appearance of masses of various sizes connected with several nerve-branches which appear to pass off from them in different directions. The ganglia situated in different parts of the body are all more or less connected by means of bundles of nerve-fibres passing between them. As already noticed, many of them are arranged alongside the spinal column ; others are si tuated on the different plexuses which are formed by the branches passing off from these, while numerous others of smaller size occur in the substance of the organs supplied by the sympathetic. All of them consist essentially of a number of bodies presenting peculiar characters and termed ganglionic corpuscles, and of nerve-fibres in more or less intimate connection with these.
Ganglionic Corpuscles, ganglion-vesicles (Germ. Ganglienkugeln).— These bodies ap pear to have been first noticed by Ehrenberg*, and were aftervvards more fully described by Valentin.t They vary in size from the —„w,th to the ,iuth of an inch. Those in the ganglia of the cerebro-spinal nerves are generally con siderably larger and not so delicate as those in the ganglion of' the sympathetic. They commonly present a round or oval form; sometimes they are more or less pear-shaped. Their contents consist of a delicate clear fluid holding in suspension numerous finely granular particles, which give the cells a more or less grayish aspect. This substance is possessed of considerable viscidity, as shown by the fact that when removed from the corpuscle it does not separate into distinct particles, but remains coherent in a single mass which flattens out somewhat. Each of the ganglionic corpuscles contains a distinct rounded nucleus which in appearance resembles the corpuscle itself, only its contents are clearer. These measure from the „175-6th to the Tauth of an inch in diameter, and are commonly situated rather towards one side of the cell. Within the nucleus there is commonly a third body, which presents a clear rounded appearance like the nucleus, and may be regarded as the nucleolus. Sometimes there are two such bodies present. In the ganglionic corpuscles there is also fre quently contained a mass of pigmentary matter consisting of particles which are much coarser and darker than the rest of the con tents. This mass is sometimes situated at a little distance from the nucleus, at other times it partly covers it, and occasionally it conceals it entirely from view. Its quantity varies much in different cells : it appears, as Kolliker observes, to be more abundant in the ganglion corpuscles of old people than in those of the young. Sometimes he has observed it present in such quantity as to fill the entire cell. In the Gasserian ganglion of a roan aged about sixty I observed several bodies present, which in size and shape corresponded with the gan glionic vesicles : they appeared, however, to be less delicate, and presented a dark-brown colour, and in all probability were ganglionic corpuscles filled vvith dark pigmentary matter such as Kelliker notices. Connected with many of the ganglionic corpuscles are one or two delicate processes of different lengths, and presenting the same delicate finely-gra nular appearance as the vesicle itself of which they appear to be a prolongation. In the corpuscles occurring in the ganglia these do not present the same branching character as they have been described to do in the brain and spinal cord by Purkinje, Remak, Hannover, and by Todd and Bowman, who in their de scription of these bodies, which by them were termed "caudate nerve-vesicles," hinted at the probability of the processes being continuous with nerve-tubes. The actual continuity of the process of the ganglion-vesicle with the nerve tube was, however, first observed by Kolliker % in the ganglia of the amphibia. He found that on tracing the process onwards froxn the cell it became continuous with a nerve-tube pre senting, distinct dark margins. The observa tion of Kelliker in regard to the connection of the nerve-tube with the ganglion-corpuscle has since been confirmed by many other ob servers, and especially by Wagner and others in the ganglia of the fish. Some of the gan glionic corpuscles appear to be destitute of any such process ; others have a single process passing off from them, while others present two such processes, passing off at either extremity (A. c.fig.286.). Occasionally the two processes pass off from a round cell, not at either extre mity, but at a short distance from each other on one side of the body (fig. 291.). The ganglionic corpuscles which are not connected with any process, or, as may be safely said, with any nerve-tube, have been termed by Stannius apolar cells ; those from which one tube pro ceeds are termed unipolar, while the cells with which two such are connected are called by him bipolar ganglionic corpuscles or cells. The nerve-tube which is connected with the uni polar cell is always found to run peripherically, e. from the centre. In regard to the bipolar them runs towards the periphery, the one at the opposite runs towards the nervous centres.