On the other hand, Ecker* has assured him self of the presence of a membrane in mam mals and birds. By the application of pot ash, the masses of granules which seem to constitute the wall of the corpuscle were dis solved ; and he then not only saw the rami fications of the arteries on the Malpighian cor puscle with great distinctness, but he also recognised that this possesses a distinct mem branous wall, in which a network of ex ceedingly fine and well-defined stripes could be detected. Although these stripes are actual fibres, yet, according to Ecker, they everywhere cover a structureless gland-mem brane, for the wall of the vesicle is never interrupted in the structureless intervals be tween these fibres ; indeed it is possible that the latter are themselves but folds of a structureless membrane. Amongst the most recent authors, Arnold 1- and Huschke t ac cept Giesker's view, and Dr. Gerlach § re peats Ecker's decision. As to myself, in the first place, I regard it as an incontro vertible fact, that the Malpighian corpuscles possess a special membrane. If one of the vesicles be isolated, and sufficiently separated from the surrounding tissues, it may be seen without any further preparation, especially with a slight pressure (fig. 527.) ; and it be comes particularly distinct if a little dilute soda or potash be applied (Ar. 528.). These reagents dissolve all the surrounding parts of the pulp, with the exception of the ves sels, and thus leave the membrane of the vesicle, although somewhat altered, yet quite entire. Concerning the nature of this mem brane, I have verified the following: it is colourless, transparent, about I to 2-1000ths of a line in thickness, has everywhere two contours, and here and there it exhibits con centric lines. Its structure so far corresponds with that of the sheaths of the vessels with which it is continuous, that it contains at least white fibrous tissue and elastic fibres ; but the unstriped muscular fibres which oc cur in these sheaths in many animals, are altogether absent from the membrane of the Malpighian corpuscle ; and the latter must especially be noticed as being much more de licate than the sheaths of the arteries on which the corpuscles sit. The white fibrous tissue, vvhich Ecker regarded as a continuous membrane, in consequence of having seen it vvhen changed by the action of potash, is in precisely the same condition as in the par titions and sheaths of the vessels, and forms by far the greatest part of the coat of the cor puscles ; while the elastic tissue (the stripes of a doubtful nature which Ecker saw) ap pears to constitute only a more or less ex tensive network of pale, so-called nuclear fibres (kernfasern) (fig. 528. b). So that the membrane of the Malpighian corpuscles would thus appear to be only a modified portion of the vascular sheath,— a view which most ap proximates to that enunciated by J. Miiller. An outer coat, of which Giesker speaks, has never been plainly verified by me as a special membrane connected with the preceding ; but it seems to me more probable, that the cor puscles are always immediately surrounded by the cells and vessels of the pulp. Certainly these vessels are often connected together by an indistinct fibrous or membranous sub stance, but this is especially present in the pulp, and is nothing else than the termination of the sheath of the vessels. The preceding remarks especially apply to the Malpighian corpuscles of the higher brute mammalia. As to those of man, although they are much more difficult to examine, yet I have satisfied my self' in the most positive manner that they correspond with those of the brute mammalia in all essential points. This is easiest and best seen in the spleens of children. The struc ture of these is exactly that seen in animals, only the coat is more delicate, so that it is extremely difficult to isolate a single cor puscle entire, and the contents are expelled by the slightest pressure. In the wall is seen the same network of elastic fibres as in ani rnals, and this renders it possible even to re cognise those which are burst. Extremely fine capillaries of 3-1000ths of a line in diameter may frequently be seen around the corpus cles ; but the latter are just as little enve loped in a second membrane as in animals.
The Malpighian corpuscles do not possess in their interior an epithelium and separated contents like the glands, but they are densely filled with a semifluid, greyish white, cohesive mass (fig. 527. b). This contains, together with a small quantity of a clear fluid, a large quantity of morphous particles, which have been very differently described by different observers. According to J. Miiller they very much resemble the corpuscles of the spleen pulp, and have a general likeness to the blood discs, but are irregularly spherical. Bischoff regards them as altogether corresponding with those of the chyle, both in appearance, size, and behaviour with water and acetic acid. According to Henle, they resemble
those of the spleen-pulp and those of the thymus and thyroid body ; and he so de scribes them, that it would appear he recog nised nuclei and a small proportion of cells. Oesterlen describes them as nuclei resernbling the elements of the pulp. Hessling, Huschke, and Nesse* agree with Bischoff' respecting the similarity of the elements in question to the lymph and chyle corpuscles. The latter of these authorities finds those of the rabbit to be 2-3-1000ths of a line in diameter, while Hessling certifies to their size in men as from 2-51-1000ths, and describes their surfaces as possessing a mulberry-like ap pearance, and their contents as partly minute granules, partly separate nuclei. J. Simon found that the corpuscles in question never attained a development into cells. Remak t describes them as consisting — partly of large transparent cells, with an interior containing a single lateral, or double and clear nucleus — partly of small, dark-bordered vesicles, closely surrounded by a delicate pale membrane, and occupied by a dark central nucleus. The first, according to him, resemble the larger, the last the smaller lymph corpuscles. Fi nally', Gerlach finds in the Malpighian cor puscles the nuclei of cells, and, in equal quan tity, cells of different sizes, with one, two, or three nuclei, as well as blood corpuscles, with all those forms of granule-cells which I shall hereafter describe as developed in the spleen pulp from the effused blood.
These are the most important accounts given by others. As the result of my own researches, I must, firstly', corroborate J. Miil ler, who explains the elements of the contents of the Malpighian corpuscles and spleen-pulp as similar structures. Also, I can add with Bischoff, that they often resemble the chyle corpuscles ; yet I am not disposed to lay any weight upon this correspondence. Further more, I consider it fully made out that Ger lach's view, according to which blood cor puscles, and cells which include blood cor puscles,are a constant constituent of the Mal pighian corpuscles, is altogether erroneous. They are not even frequent occurrences, for in many animals I have not found them at all ; and when they occurred — as, for instance, in oxen—they were mostly found in scattered vesicles, and, further, were in such small quantity, that they had no influence on their colour. And very often blood corpuscles and their metamorphoses appeared to occupy the vesicles, where a more careful examin ation showed that they were only in C011 tact with their outer surface. The degree of accuracy to which Gerlach's assertion may lay claim is best shown by the fact, that he al together denies the existence of these granule cells (which are produced from the effused blood) in the spleen-pulp ; while it is here, as well in these as in animals which possess no proper spleen vesicles, that they occur in the greatest quantity, and are most easily seen.
The constant and essential elements of the splenic vesicles are cells, with a single nucleus of a spherical shape, and from 3 to 5-1000ths of a line in diameter : besides these, free nuclei, and larger cells of 6-1000-ths of a line in diameter, and with one or two nuclei, also occur (fig. 529.). The cells are in general pale and faintly granular ; their nuclei are from 16 to 25-10000ths of a line in size, spherical, apparently homogeneous, and with a rather dark margin ; or frequently vesicular, with a more or less distinct nucleolus and other granules. It is not infrequent to see single cells provided with dark fatty granules, and in particular instances blood discs are present, either changed or unchanged, free or included in cells. The free nuclei are of the same size as those contained in cells, and are also, in other respects, quite similar to them. In the ordinary- method of examining the Malpighian corpuscles, the quantity of them nuclei seems larger than it really is, since many of the cells burst, and allow their nu cleus to escape. Yet it is very remarkable that their number is very variable in the most cautious examination, a fact which appears to me partly to account for the very different statements of different observers. In many cases it has hhppened to me to find only a few free nuclei, often none at all, while in other instances they constitnte a half or more of the elements of the corpuscles. This fact, taken together with the often very different size of the cells present, seems to prove that a continuous process of cell-growth exists in the Malpighian corpuscles ; in such wise, that new nuclei and cells continually arise, and old cells perish. But hereof more will be said in speaking of the pulp, in which the same pro cess obtains.