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work would find its way between the cells and the tube of membrane to the margin of the lobule. Upon the other conclusion, which supposes that the cells lie freely in the meshes of the capillary network, the bile formed in the more central part of the lobule is supposed to be transmitted from cell to cell, until at last it reaches those at the circumference of the lobule, and it is further concluded that, in its transmission, it becomes elaborated, by being acted upon by each successive cell of the series. If, then, bile were formed by being passed on from cell to cell in this manner, the materials from which the crude bile is first formed ought to be separated from the blood in the more central parts of the lobule; for otherwise, the blood, rich with recently absorbed constituents, would seem to pass through a considerable extent of that portion of the capillary network at the circumference of the lobule to no purpose.

If the above description of the anatomy of the parts be correct, the precise point of the most active formation of bile should be the outer part of the lobule, for the blood reaches this part first. It will be shown subsequently that this is probably the case. Argument alone would render the existence of such a membrane probable, but, with care, its presence may be actually demonstrated, and by several different methods of preparation.

CONTENTS OF THE TUBULAR NETWORK OF BASEMENT

MEMBRANE.

The most important anatomical elements contained in the tubular network of basement membrane are the liver cells; but, besides these, a certain quantity of free granular matter is always present; and not unfrequently oil globules, and granules of dark yellow colouring matter, are met with. In disease, it is not unusual to find the network occupied by a viscid, granular, highly refractive mass, in which only a few nuclei can be observed. Sometimes the network is so shrunken as not to be more than half the diameter of an ordinary healthy hepatic cell, and its contents appear to consist of a viscid material, in which are suspended granules and oil globules. In fishes generally, the tubular network seems to be greatly distended, and entirely occupied by a

mass of oil globules. With care, however, nuclei may sometimes be distinguished among them.

Cells. The liver-cell varies much in form and size in different animals, and in the liver of the same animal. Its characters have been well described by numerous authors. The cells in different parts of the lobule vary in their characters, as Dr. Handfield Jones has especially pointed out.* The largest cells are not unfrequently as much as the 1-800th of an inch in diameter, the smallest not more than 1-2000th of an inch, or even less.

Each cell contains a nucleus, demonstrated easily in perfectly normal cells; but not to be readily distinguished when the cells contain much oil, and when they have undergone other changes in the course of disease. The nuclei vary considerably in size. Upon an average, they may be said to be about the 1-3000th of an inch in diameter. Generally they are circular, but sometimes they have an oval form. The nucleus contains granules, some being larger than others; often there is a bright point in the central part, which is regarded as the nucleolus.

Each liver-cell of the adult liver usually contains but one nucleus; but, in some instances, two may be observed. The livercells of young animals, on the other hand, commonly contain many nuclei. I have observed as many as six or seven in the cells of the calf, about the middle period of gestation.

Contents of the Cell.-In all the animals which have fallen under my notice, the liver-cells, compared with the cells of other glands, are remarkable for their variety of form and size, for their high refractive power, and for containing besides the nucleus, granular matter, and, very frequently, oil globules and granules of yellow colouring matter. Under some circumstances the yellow colouring matter becomes much altered, and so dark, that the cell appears to be occupied by black granules, which are sometimes The material of which the cell consists is not of very numerous. a fluid nature, but highly viscid; so that, upon pressure, the whole cell becomes flattened, and the highly refractive viscid material is

* For the views of Dr. Handfield Jones upon the function of the liver-cell, the reader is referred to his valuable papers in the Philosophical Transactions, 1846, 1849, and 1853, and to a paper in Vol. XXXV. of the Medico-Chirurgical Transactions, 1852.

still seen to form a thin compressed layer. The cells are rounded, oval, or polyhedral in form, and frequently present many irregular angles, with somewhat rounded edges. Not unfrequently the appearance is such as would give one the idea that the cells had been packed together very closely, and thus subjected to pressure unequally distributed. I have not succeeded in demonstrating to my satisfaction the existence of a distinct cell-wall; but at the same time have not yet investigated the matter sufficiently to enable me to express a confident opinion that it does not exist. If the absence of this structure were placed beyond a doubt, the so-called cells must be regarded as fragments broken off from a solid, more or less cylindrical mass, originally continuous, in which nuclei were interspersed at intervals,-a view which accords in some degree with that held by E. H. Weber.

*

Contents of the Tubular Network in Fishes.-Now, in the class of fishes, and in some reptiles and birds, and, according to Dr. Handfield Jones, even in the rat, the tubes of the cellcontaining network do present the appearance of being filled with an uninterrupted mass, composed of oil globules, granular matter, nuclei, and sometimes coloured granules. In fig. 55, which is a drawing of the tubes of the cell-containing network of the common eel (Anguilla acutirostris), this point is well shown. The drawing was made with the neutral tint glass reflector; and I have the preparation now in my possession, so that it can be readily compared with the delineation. Here the tubes are seen filled, but not distended with oil globules. The high refractive power of the latter prevents the possibility of seeing the nuclei in situ; but in the fluid surrounding the preparation a few were distinctly observed. The eel from which this specimen was taken had been kept for some time without food.

From this preparation the disposition of the contents of the tubular network in fishes is well shown; and it demonstrates, in an uninjected preparation, the existence of the tubular membrane, so difficult to show in this class of animals. Fig. 54 is a drawing of the capillaries of the eel's liver injected, and their arrangement is observed to be similar to that in most animals. The tubes containing the oil globules, represented in the adjacent drawing, form *Phil. Trans., 1849.

a lax network with very long meshes, or perhaps the specimen might be more correctly described as being composed of parallel tubes, communicating with each other here and there. Now, how can the evidently cylindrical lines of oil globules, depicted in fig. 55, lie in the meshes of this vascular network, unless they be contained within a tube of basement membrane? Of the accuracy of the facts there can be no doubt, and the preparations from which the drawings were made may yet be compared with each other. The only interpretation I can offer is that which I have just advanced, and it seems impossible to associate the two appearances as they exist in nature in any other manner.

In a large number of animals, then, the contents of the tubular network may be said to be continuous; in some it is interrupted so as to form masses irregular in size, in which nuclei are scattered at intervals; and in others, the particles are more uniform in size, resemble each other very closely in general character, and each contains a separate nucleus. Between the numerous, well-defined, and separate masses, or liver-cells of the mammalian animal on the one hand, and the continuous mass which occupies the tubular network of the fish on the other, it is easy to demonstrate every intervening shade of difference; and more than this, at different periods of development of the embryo, and in various morbid conditions of the human liver, every degree of separation and of continuity may be observed. Again: by the action of various chemical reagents, as described in page 40, separate cells of the healthy mammalian liver fuse, as it were, so as to form continuous masses, ing the tubular network of fishes.

the distinct and may be made to like those occupy

In all cases there is room for fluid to pass between the contents of the tube and its walls towards the duct, as may be proved by the passage of injection; and, although to our observation the tubes may appear to be quite full, or even distended, it is obvious that, independent of any change of size in the cells themselves, a very slight diminution in the quantity of blood in the capillaries of the liver would permit the free passage of fluid along these apparently distended tubes.

The facts I have stated tend to lead to the conclusion, that the

liver-cell is rather to be regarded as a collection of viscid matter round a central nucleus, than a true cell provided with a distinct cell wall. There are many circumstances in favour of such a view, but I shall not now bring these forward, neither shall I attempt to offer a positive opinion on the matter until some observations I am making are completed. I may, however, be permitted to observe that, although such a conclusion would be altogether at variance with the results of the observations of almost all previous observers, and if true of the liver-cell, must also be true of the cells of renal epithelium, and of those of some other glands,-it would be, in some measure, in accordance with a view upon the nature of cells lately advocated by Professor Huxley.

*

Of the manner in which the Cells are arranged within the Tubular Membrane.-In the livers of adult mammalia which I have examined, the cells for the most part lie in a single row, although, as before observed, some portions of the network have been found to contain two or three rows lying across the tube, while in other situations the space within the tubular membrane is so contracted as not to admit one cell of the ordinary size, in which case it is occupied only by granular matter, and a viscid material which refracts highly. The following mammalian livers have been examined with reference to this point,-that of the human subject, pig, dog, cat, rat, rabbit, horse, seal, and some others.

I have never seen such an appearance as has been delineated by Leidy, who has represented three cells lying across the tube; nor have I observed anything agreeing with the description or drawings of Lereboullet, who figures two rows of cells, and represents a mass of injection passing between them. My own observations lead me to conclude that the cells lie somewhat irregularly, as above described, and differ totally in their arrangement from that of the renal tubes, where there is a central cavity. Bile would escape from the cells, and pass probably in an irregular manner, sometimes on one side of the tube, sometimes on the other, between the cell and the wall of the tube;-at least this is the way in which injection can be made to pass in the direction opposite to that in which the bile flows naturally.

* The Cell Theory, by T. H. Huxley, F.R.S., Medico-Chirurgical Review, October, 1853.

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