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, J *rgo cand&te nerve cell, with smaller cells and nerve fibres, from a thin transverse s»-ctiou of the lower r.an, ot the grey matter of the medulla oblongata of a young dog. 1 be specimen bad baen soaked for some weeks in aortic acid and glycerine. The lines of dark granules resulting from the action of the ac:d aw seen passing through the very substance of The cell in v^ry defiuit/a directions. Thus the cell i* The point where lines ircm several distant parts intersect (Diagram, Fig 2). It is probable that each of these lines is but a portion of a complete- circuit {see Diagram in F18 3). A, A, A, large fibres which leave the cell. B. a fibre irom another cell, dividing into finer fibres, exhibiting several lines of granules. C.C.C, fibres from a younger caudate nerve vusicLti. D. fine and flattened dark-bordered fibres, E. three Stio nerve fibres running together in a matrix of connective usauv. F, F, F. capillary vessels.

ode of development. In this paper I propose to describe some points of terest in connexion with their structure. In the first place, however, I ould remark that there are neither 'cells' nor 'Besides' in the ordinary •ceptation of these words, for there is no proper investing membrane, either are there 'cell-contents' as distinguished from the membrane or ipsule; in fact the so-called cell consists of soft solid matter throughout, he nerve-fibres are not prolonged from the nucleus or from the outer part f the cell, but they are continuous with the very material of which the ubstance of the ' cell' itself is composed, and they are, chemically speaking, f the same nature. So that in these caudate cells we have but to reco"iize the so-called 'nucleus' (germinal matter) and matter around this formed material) which passes into the 'fibres,' which diverge in various lirectiuns from the cell: see Plate III. (fig. 1).

At the outer part of many of these 'cells,' usually collected together in me mass, are a number of granules. These are not usually seen in the i tiling cells, and they probably result from changes taking place in the matter of which the substance of the cell is composed. But it is not proposed to discuss this question in the present paper.

My special object in this communication is to direct attention to a peculiar appearance I have observed in these cells, which enables me to draw some very important inferences with reference to the connexions and action of these very elaborate and most important elements of the nervous mechanism.

In some very thin sections of the cord and medulla oblongata of a young dog, which had been very slowly acted upon by dilute acetic acid, the appearances represented in Plate III. (fig. 1) were observed. Subsequently, similar appearances, though not so distinct, have been demonstrated in the caudate nerve-vesicles of the grey matter of the brain of the dog and cat, as well as of the human subject. I have no doubt that the arrangement is constant, and examination of my specimens will probably satisfy observers that the appearance is not accidental. Ench fibre (a, a, a) passing from the cell exhibits in its substance several lines of granules. The appearance is as if the fibre were composed of several very fine fibres imbedded in a soft transparent matrix, which fibres, by being stretched, had been broken transversely at very short intervals. At the point where each large fibre spreads out to form the body of the cell, these lines diverge from one another and pursue different courses through the very substance of the cell, in front of, and behind, in fact around the nucleus. Lines can be traced from each fibre across the cell into every other fibre which passes away from it. The actual appearance is represented in Plate III.; and in the diagram, fig. 2, a plan of a 'cell,' showing the course of a few of the most important of these lines which traverse its substance, is given.

I do not conceive that these lines represent fibres structurally distinct from one another, but I consider the appearance is clue to some difference in composition of the material forming the substance of the cell in these

VOL. XIII. 2 F

particular lines ; and it seems to me that the course which the

permits of but one explanation of the appearance. Supposing nerve-cm-'

rents to be passing along the fibres through the substance the celt

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A diagram of such a cell as that represented in Mate III. (fig. 1), showing the prh cipal lines diverging from the fibres at the point where they become continuous witi the substance of the coll. These lines mar be traced from one fibre across the ea4 and may be followed into every other fibre which proceeds from the cell. .

they would follow the exact lines here represented; and it must be noticed that these lines are more distinct and more numerous in fully-formed tbtt in young cells. They are, I think, lines which result from the frequent passage of nerve-currents in these definite directions.

Now I have already advanced arguments in favour of the existence of complete nervous circuits, based upon new facts resulting from observations upon a, the peripheral arrangement of the nerves in various tissues*; ithe course of individual fibres in compound trunks, and the mode of branching and division of nerve-fibresf; and c, the structure of ganglioncells J. I venture to consider these lines across the substance of the caudate nerve-cells as another remarkable fact in favour of the existence of such circuits; for while the appearance would receive a full and satisfactory explanation upon such an hypothesis, I doubt if it be possible to suggest another explanation which would seem even plausible.

Nor would it, I think, be possible to adduce any arguments which would so completely upset the view that nerve-force passes centrifugally from one

* Papers in the Phil. Trans, for 1860 and 1862. Lectures on the Structure ol tk Tissues, at the College of Physicians, 1860.

t " On very fine Nerve-fibres, and on Trunks composed of Tery fine Fibres alone," Archives of Medicine, vol. iv. p. 19. *' On the Branching of Nerve-trunks, and of the subdivision of the individual fibres composing them," Archives, vol. iv. p. 127.

} Lecture* at the College of Physicians. Papers in Phil. Trans, for 1862 and 1S63.

.1, as from a centre, towards its peripheral destination, as this fact. So - from the fibres radiating from one cell, or from the nucleus as some ppose, in different directions, all the fbres which reach the cell are comex, and contain lines which pass uninterruptedly through it into other t-rea. Instead of the cell being the point from which nerve-currents •diate in different directions along single fibres, it is the common point here a number of circuits having the most different distribution intersect, oss, or decussate. The so-called cell is a part of a circuit, or rather of great number of different circuits.

Fig. 3.

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Diagram to show the possible relation to one another of various circuits traversing a single caudate nerve-cell, a may be a circuit connecting a peripheral sensitive surface with the cell; 4 may be the path of a motor impulse; c and d other circuits passing to other cells or other peripheral parts. A current passing along the fibre a might induce currents in the three other fibres, J, c, d, which traverse the same cell.

I conclude that at first the formed material of the cell is quite soft and almost homogeneous, but that as currents traverse it in certain definite lines, difference in texture and composition is produced in these lines, and perhaps after a time they become more or less separated from one another, and insulated by the intervening material.

It may perhaps be carrying speculation upon the meaning of minute anatomical facts too far to suggest that a nerve-current traversing one of these numerous paths or channels through the cell may influence all the lines running more or less parallel to it (fig. 3).

I have ascertained that fibres emanating from different caudate nervecells situated at a distance from one another (fig. 4, a, a) at length meet and run on together as a compound fibre (A, b, b), so that I am compelled to conclude (and the inference is in harmony with facts derived from observations of a different kind) that every single nerve-fibre entering into the formation of the trunk of a spinal nerve, or single fibre passing from a

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