The cells of the spleen-pulp, which I shall call " parenchyma-cells of the spleen," have been described by J. Miiller as similar to those of the Malpighian corpuscles ; and, as was previously stated, this view has been followed by the majority of writers ; as by Ilenle, Bischoff', Huschke, Remak, and others. Only Von Hessling and Gerlach are of another opinion. According to the former, the globules of the spleen-tissue are distin guished by their dark colour, and by their being mingled with spindle-shaped cells. Ger lach finds that cells with nuclei are rare in the spleen-pulp ; while, on the contrary, he considers them to be frequent in the Mal pighian corpuscles. As to myself, I have already expressed my concurrence with the view taken by Willer, and may therefore for bear to enter further upon this point ; never theless, it is necessary to remark that the parenchyma-cells exhibit some additional peculiarities, which ought not to be passed over without notice, A considerable por tion of these cells completely correspond with the cells of the spleen vesicles ; the characteristic appearances of which are their roundness, their size — from 3 to 5-1000ths of a line —their paleness, and their dark nucleus (fig. 330. b). On the other hand, smaller and larger corpuscles also occur in the spleen-pulp, which are never met with in the Malpighian corpuscles. The former are small round corpuscles, somewhat larger than blood globules. They are seen in one of two states either they exhibit a membrane and nucleus inseparable from each other, and thus, apart from their colour and somewhat lighter outline, resemble blood globules ; or they are free nuclei, in which no nucleoli are visible. But only a few of these are free nuclei, for by the application of saliva or a little water a membrane starts into view, either completely enclosing them, or limited to one side (fig. 530. a). The nuclei, which thus appear as something separate from the membrane, have always the dark appearance of those cells the two parts of which are inseparable from each other • so that the appearance of these latter seem chiefly dependent on the nucleus. With these small and quasi-developing cells, one also meets with free nuclei ; and careful manipulation of the preparation shows these to be in general more numerous than in the Malpighian cor puscles (fig. 530. c). The larger named cor puscles are partly pale cells of 7-1000ths of a line in size, with one or two nitclei; or granule cells of 4 to 6-1000ths of a line, an'd vvhich may be described as " the colourless granule cells" Cfig. 530. d): both of these are more frequent than in the Malpighian corpuscles. The spindle-shaped or fusiform cells which Hessling mentions do not belong to the normal constituents of the spleen-pulp, and are nothing else than epithelium cells of the splenic arteries (fig. 534. b), which in ma cerated specimens of the human spleen, and in preparations where the vessels have been cut through, easily get into the pulp, and give rise to the delusive appearances of the so-called fusiform cells. The comparative examination of this part of the spleens of many animals confirms what has been al ready stated of the elements of the Malpi ghian corpuscles ; namely, the elements of the pulp vary greatly, since sometimes the nu clei, sometimes the smaller cells, sometimes the greater cells, predominate. And in this, as in the former case, I conclude therefrom that a continuous process of cell growth ob tains in the spleen, by which new cells are formed around nuclei, and old ones dis appear.
The quantity of parenchyma-cells of dif ferent kind and shape, and of free nuclei which must be reckoned with these, is a very considerable one; so much so, as to con stitute nearly one half of the whole red spleen substance. These do not lie collected in large heaps, but constitute small irregular groups of different size, which occupy the interspaces formed by the partitions of all sizes, the vessels, and the Malpighian cor puscles. The best method of representing this disposition is to regard each part of the pulp, which is included in a large mesh by trabeculae visible to the naked eye, as con stituting in a small form what the spleen itself is in a larger. The microscopic par
titions and fibres and the finest vessels thifs exhibit the same relations as the larger par titions and vessels ; while the small nests of parenchyma-cells answer to the large homo geneous masses of red pulp which are visible to the naked eye. There are nowhere any special coats which include these cells, but they may be seen everywhere placed imme diately on the sheaths of the vessels, the par titions, and the membranes of the Malpighian corpuscles. In the above delineation of the parenchyma-cells, those of man and of the higher mammalia have especially served as the model: but in general a complete simi larity obtains in other animals ; and it is only here and there that any specialities show themselves. In many animals — thus, for instance, in amphibia — the spleen has often, though not always, very beautiful pa renchyma-cells with large nuclei : in birds, and in the scaly Reptilia, granulated and somewhat dark cells are for the most part more frequent. In the hedgehog, rabbit, and guinea-pig, some cells, which are altogether peculiar, occur in company with the ordinary ones. In both the former of these I saw, here and there, large round cells from 10 to 16-1000ths of a line, with three, four, to ten or more nuclei, which often lay so closely together in the middle of the cell that they appeared to make up a mulberry-like mass, like certain large cells which one finds in the marrow of young bones. These cells were by no means uncommon, but gradually dimi nished itf.size towards that of the parenchyma cells. In the guinea-pig occur round cells, in large quantity, of 48 to 60-10000ths of a line, which contain one or seldom two round granules of a dark contour ; and their nu cleus, not always very distinctly visible, is very plainly seen on the application of acetic acid; while, at the same time, the dark granules often disappear.
The blood (fused in the spleen-pulp, as well as the metamorphoses of the blood globules in the same, demand the greatest consideration both in respect of anatomy and physiology. I believe myself to have been the first who* directed attention to this circumstance, and cor rectly recognised it ; although Oesterlen, Re mak,and HandfieldJones had already detected isolated facts having a reference to it. Oester len* was the first who found in the spleen of frogs and toads, and with less distinctness in that of the mammalia, yellow, rose-red, and black minute corpuscles, but he was not in a condition to explain them. Remak followed next without greater success ; he found in the spleen-pulp of the calf delicate trans parent vesicles, with 1 to 3 round, reddish yellow homogeneous bodies, the colour of which approximated to that of the blood corpuscles, but which were not so easily swollen out by water. Finally, Handfield Jones t discovered peculiar yellow corpuscles in the spleen of different vertebrata.
All these facts are placed in their true light by my discovery that blood corpuscles are almost constantly undergoing dissolution in the spleen and disappearing. This will be shown as follows : — The red pulp of the spleen in man and animals exhibits at different times a different colouring, or rather a different condition of the blood corpuscles contained in it, and these, without any participation of the other elements, affect its colour by the different nature of their appearances. Thus, in a par ticular animal or in the human subject, this sub stance sometimes possesses a paler or more greyish red, sometimes a brown, or even black-red colour : in the latter case a quan tity of altered blood globules are present, the appearances of which will hereafter be de scribed ; while in the former case, it may easily be proved by the microscope that the red colour depends on unaltered blood globules, which are easily separated from the pulp by pressure, and on the application of water give off all their colour in a short space of time. In other animals, the spleen has always about the dark colour mentioned : nevertheless, even in these cases, sometimes only un changed blood globules are seen ; sometimes many of these are undergoing the most manifold changes.