Notwithstanding so many important points have been established, it must be confessed that much remains to be decided. Thus, for example, we perceive that the ganglion of Meckel, like the ganglions of the sympathetic in the neck, has connected with it a motor fibril ; but this fibril, as Arnold has observed, presents the whitish character and firm texture common to the cerebro-spinal nerves, and therefore, it must be presumed, passes from the portio dura to the ganglion, whilst the twigs uniting the cervical nerves and the sympathetic are reddish and soft, rendering it probable, as Fletcher supposes, that they are furnished by the ganglia.
Such being the imperfect results of ocular inspection, we are naturally anxious to obtain more exact information, especially in reference to the character of the different orders of fibres which are connected with the ganglia. The microscopical observations which are being car ried on at this time with so much zeal in Ger many, and from the prosecution of which the most valuable evidence may be anticipated respecting the undecided points of minute anatomy, have already thrown some light on this interesting question. Thus Ehrenberg de tected in the sympathetic not only the varicose fibres which some imagine are proper to that system, but also some of the cylindrical fibres of which the cerebrospinal nerves are principally composed. According to Lauth and Remark, the nerves of organic life (i. e. of the sympa thetic) consist for the most part of varicose fibres mixed up with a small proportion of cylindrical; whilst those of animal life consist principally of cylindrical mingled with a few varicose fibres. This is the exact appearance which must have been anticipated, if the mu tual interchange of fibres described by Bichat,t W. Mayoh Fletcher,11 and others, really exist.
It may here be remarked that although the accuracy of Ehrenberg's researches, confirmed as they have been by Muller, Purkinje, Valen tin and others, is called in question by Krause, Berres, and Treviranus, yet the essential fact of there being a decided difference in the phy sical character of different orders of nervous fibres, and, consequently, a test for their suc cessful analysis, is universally admitted.11 Lastly, it is a question of great interest whether there are not, independently of the relations which exist between the sympathetic and the cerebro-spinal axis, fibres proper to the former, which establish between them and the organs they supply with nerves most important con nexions. Our present knowledge does not
afford the means of solving this question; and, although my attention has been particularly directed to this subject, still, as my observa tions are as yet incomplete, I shall satisfy myself by expressing my conviction that such a system of nervous fibres does exist.
Covering.—Evcry ganglion possesses two coverings: the outer one in the spinal ganglions is very firm, being derived from the vertebral dura mater, whilst in the sympathetic gan glions it is composed of condensed cellular tissue. On raising very carefully the external capsule, a more delicate tunic is exposed, which adheres to the proper ganglionic tissue.
Bloodvessels.—These bodies, like all other parts of the nervous system, are amply sup plied with arterial blood. After a successful injection, two, three, or more arteries, derived from the neighbouring vessels, may be readily observed running to the ganglion. Each vessel, having perforated the coverings of the ganglion, forms according to Wutzer a plexus on the inner surface of the capsule, and at length sends de licate branches into the pulpy matter, which, with the aid of the microscope, may be ob served to run in the same direction with the nervous filaments. The exact mode in which these vessels terminate is unknown, but it is probable, as in the cerebro-spinal system, that each nervous fibre is accompanied by a mi nute artery and vein. No lymphatics have been demonstrated, but analogy tends to prove their existence, and Lobstein states that he has often seen them forming networks around the ganglions.
Chemical composition. —The experiments performed by Bichat* and Wutzert would tend to show that the substance of the ganglions is distinct in its qualities from the cerebral matter and also from that of the nerves. By boiling, it is at first hardened, but soon becomes softened ; maceration in cold water renders it more soft and pulpy, and if sufficiently prolonged, the water being frequently changed, it is converted into adipocire. It is liquefied by the alkalies, and is rendered crisp and hard by the adds and alcohol.