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In the first part of their course, therefore, the processes of the ganglion-cells, especially in the brain and spinal marrow, are not nerves in the ordinary meaning of the word, but pale fibres which frequently bear scarcely any resemblance to the non-medullated fibres I have already described to you, and have rather the appearance of pale axis-cylinders (Fig. 88, a, b).

It was long believed that essential differences existed between the ganglion-cells according as they belonged to one or other of the three principal divisions of the nervous system, and therefore especially between the cells of the sympathetic and those of the brain and spinal marrow. But in this point also the contrary has proved to be the case, especially since Jacubowitsch has brought to our knowledge the new fact, of the correctness of which I have fully convinced myself, namely, that structures which are perfectly analogous to the ordinary ganglion-cells of the sympathetic, also occur in the middle of the spinal marrow and several parts which are considered to belong to the brain. It may therefore be said, that cells belonging to the sympathetic nerve, concerning which it has already long been known that a great part of its fibres have their origin in the spinal marrow, are really also met with in the spinal marrow, and that in this respect also the cord does not form a simple and necessary contrast to the main trunk of the sympathetic.

If we examine the spinal marrow, which affords the clearest representation of the plan of a true nervous centre in the narrowest meaning of the word, a little more closely, we everywhere find in its grey substance (the horns), and indeed in nearly every transverse section, different kinds of ganglion-cells. Jacubowitsch has, and I believe him to be in the main correct, distinguished three different forms, of which he calls the one motor, the second sensitive, and the third sympathetic. These lie generally in separate groups.

I shall revert to this subject when I come to speak more

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at length concerning the spinal marrow; here I only wish to speak about the different forms of ganglion-cells. The so-called unipolar forms, are, in proportion as the examinations are conducted with more care, continually becoming more and more rare. In the great nervous centres most of the cells possess at least two processes, and very many are multipolar or, more accurately, many-branched [polyclonotis).* A multipolar cell is a body with a large nucleus, granular contents and, if it be particularly large, a spot of pigment, and is provided with processes running in different directions. These processes often divide into twigs and thus commences the condition of which I have already spoken (p. 253), that whole masses of filaments or fibres proceed from one point—a condition which indicates, that, in the first instance indeed according to circumstances, one path or another can be made use of, but that, when once a path has been chosen leading in the direction of the periphery, the impulse must be propagated in a relatively equable manner throughout the whole series of ramifications. These multipolar forms (Fig. 89, A) are mostly comparatively large, and lie accumulated in those parts which are subservient to the motor functions; and they therefore may be briefly designated motor cells.

Those forms which correspond to the sensitive spots (Fig. 89, B) are usually smaller and do not present such an extraordinary luxuriance of ramification as the larger ones. A large portion of them possess only three, or perhaps, four branches. Those which Jacubowitsch has called sympathetic are, on the other hand again, larger, but have still fewer

Fig. 89. Ganglion-cells from the great nervous centres; A,B,C from the spinal cord, from preparations belonging to Herr Gerlacb, D from the cortex of the cerebrum. A. Large, many-rayed cell (multipolar, polyclonous) from the anterior horns (motor cell). B. Smaller cells with three large processes, from the posterior horns (sensitive cells). C. Two-rayed (bipolar, diclonous), more rounded cell, from the neighbourhood of the posterior commissure (sympathetic cell). 300 diameters.

K\uv, wvof, a shoot, twig.—Tit.

branches and are distinguished by a greater roundness of shape. These are differences which are certainly not so decided, as to enable us already at once to determine in every "single case from the appearance of a ganglion-cell to which category it belongs; but still, if we consider the individual groups, they are so striking, as to incite the observer to reflection upon the different qualities of these groups. In the course of time probably further distinctions, perhaps even in the internal economy of these cells, will be detected, but at present nothing more can be stated concerning them. This is a very great and lamentable void in our knowledge, and a void which we now particularly feel, because this is just the place where we should have to discuss the specific action of these different elements. But it must not be overlooked that these conditions are among the most difficult which are ever submitted to anatomical investigation, and that one's endeavours to produce specimens of a character to convince one's own eyes alone, nearly always fail, because it is scarcely possible to succeed in effecting a real isolation of the cells with all their processes and connections, and because, on account of the extraordinary fragility of these bodies, one is nearly always compelled to trace them out in hardened sections. When sections are made of structures which to a great extent are composed of fibres and in which these run in a longitudinal, a transverse, or an oblique direction, so that an interlacement is always presented to the view, it depends of course entirely upon a happy chance whether in a section the course of a single fibre can be followed up over a large space with a certain degree of distinctness. This difficulty can certainly be lessened by making the sections in all possible directions and thus increasing the probability of at last stumbling upon the direction followed by the divisions of a branch, but even then the obstacles still remain so great that one can hardly expect, ever to be able to take in at


one view the whole of the ramifications and connections of a cell belonging to the great nervous centres, that is provided with at all a large number of branches.

In this respect also the electrical organ of fishes has become a particularly interesting subject for investigation, inasmuch as the one fibre which supplies the organ has been traced back by Bilharz to a single central ganglioncell, which is so large that it can be dissected out with the naked eye. This ganglion-cell has also delicate offsets in other directions, but it has not hitherto been possible to determine their ultimate relations any more than we are able to obtain a definite notion of the minute anatomy of the human brain, and especially to discover, to what extent connections take place there between the different cells. By the investigations which have been instituted into the structure of the spinal cord, it has been shewn to be extremely probable, that all the processes of the individual ganglion-cells do not become continuous with nerve-fibres, but that a part of them run to other ganglion-cells and thus establish a communication between the cells. Moreover at certain points, especially in several parts of the surface of the brain, still finer processes are found, which proceed from ganglion-cells and are connected with peculiar, quite characteristic apparatuses (bacillar layer of the cerebellum and cerebrum), which offer the greatest resemblance to those in the retina, those extremely delicate, vibratory arrangements of the radiating fibres.

The processes of the ganglion-cells might therefore, I think, be divided into three categories; genuine nerve-processes, ganglion-processes, and those of which the import is entirely unknown and which, it would seem, are connected with peculiar and altogether specific apparatuses, concerning which it is for the present uncertain, whether they are to be regarded as the terminations of the nerves, or only as structures placed in apposition to them.

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