This juicy or gelatinous substance, which is met with in the spinal as well as in the sympa thetic ganglia, does not, however, according to Lobstein, appear to be an essential part of the organization, as it varies in its proportion in different ganglia, and may even be absent ; nor, it is said, can it be assimilated with the grey matter of the brain.
Ehrenberg also controverts the opinion that the ganglia resemble the grey part of the brain ; but although he has found by microscopical inspection, that these bodies contain an over whelming proportion of large varicose tubes, similar to those of the fibrous portion of the brain, yet he has also shewn that they possess minute varicose fibres like those if the grey substance ; and what particularly is deserving of notice, he has detected in the muscles of the fibres granules similar to those which are found in the cervical portion if the braia.t Notwithstanding these and other high au thorities, the researches of many recent writers, which have thrown so much new and valuable light on the mutual relations of the component parts of the nervous system, leave little room for doubting the identity of these two sub stances. The analogy of the whole nervous system tends to prove that this peculiar matter is nothing else than the grey substance ; in the Gasserian ganglion, indeed, the resemblance is so striking that no doubt of their identity can be entertained. This view of the subject was taken by Winslow, Johnstone, and others ; and lately the existence of grey matter has been admitted by Dr. Fletcher, an assumption, indeed, which is the basis of his hypothesis, that the ganglionic system of nerves is the im mediate seat of irritability.* . II. Fibres.—This is a most important branch of the present inquiry, because a knowledge of the connexions of these bodies with the other parts of the nervous system and with each other, as well as of the internal disposition of their fibres, is indispensable to the investigation of their functions. The subject may be re solved into two questions. a. What is the arrangement of the fibres in the ganglia ? b. What is the nature of the fibres which are connected with the ganglia? a. The internal disposition of the nervous filaments, owing to the very intimate relations subsisting between them and the grey matter, is difficult to determine ; and hence it has happened that great difference of opinion pre vails on this point. I shall in the first place
describe the arrangement in the most simple of these organs, and for that purpose shall select that of the portio major of the fifth pair. On inspection it is seen that the large coarse fibrils of the nerve on approaching the ganglion begin to spread out from each other, and although in its interior they are, as we have already observed, encrusted by the grey matter, yet, on scraping this away, the fibres may be seen still passing on uninterruptedly, but becoming more and more separated from each other. It is this disposition which Scarpa has aptly enough compared to a rope the two ends of which remain twisted, whilst in the middle the component threads are unfolded and pulled asunder. A similar, but less distinct arrange ment exists in the spinal ganglia.
Although the continuity of the fibres through the ganglion is easily demonstrated, yet it would be wrong to conclude that this passage is all that happens ; for in the first place the three branches of the trigeminal nerve which emerge from, are decidedly larger than the trunk of the same nerve which passes into the ganglion. Their physical qualities are also altered, especially as relates to their colour, which, instead of having the whitish aspect common to the proper fibres of the cerebro spinal axis, is for some distance of the reddish hue .proper to the ganglionic system ; and again it would be in opposition to all our notions of the properties of the grey matter to imagine that the fibres do not maintain intimate connexions with that substance, by which means its influence, whatever it may be, is communicated to those threads.
In the sympathetic ganglions the internal formation is much more intricate ; and it is especially in reference to these bodies that so much diversity of opinion prevails among anatomists. The researches of Monro,* Searpa,1 and Lobstein,t as well as ocular inspection, prove that some fibres undoubtedly pass without interruption through the ganglion.