The first account of those peculiar whitish corpuscles, discovered by Malpighi and to be met with, more or less distinctly marked, in the spleen of every animal, which at all satisfies the requirements of modern anatomical science, was given by Professor Müllier, in his Archiv. for 1834. Müller describes with great accuracy the mode in which these bodies are supplied by minute arteries, and explains that they are, in fact, outgrowths of the adventitious tunic of those arteries. He states that, by means of fine injections, he found that “the arterial twigs sometimes passed by the side of the Malpighian bodies without giving off any branches to them—sometimes went straight through the whole body or a part of it, in which case, however, no portion of the arteries terminated in them. These fine arterial twigs appear less to pass through the middle of the corpuscles than to run on their walls and then to leave them. When an arterial twig divides into many minute branches in the Malpighian body, which never takes place upon its surface, but always in the thickness of its walls, these arterioles pass out again to be distributed as very minute branches in the surrounding red pulp : in fact, the ultimate termination of all the finest penicellate arteries is in this red substance. From all this I have become convinced that the white bodies, as mere outgrowths of the tunicœ adventitiæ, have no relation with the finest ramifications of the arteries.”

With regard to another important point,—whether the Malpighian bodies are hollow or solid—Professor Müller’s statements are less definite. In the commencement of his article he affirms, in opposition to Malpighi and Rudolphi, that they are solid, but at the end he qualifies this opinion : “I was long of opinion that the white bodies are not hollow, but merely filled with a white pulpy substance, which might indeed be pressed out of them, but was not distinctly defined from the walls of the bodies. Further observations recently made, however, have instructed me that the white granular substance which is contained in the Malpighian bodies is too fluid, while on the other hand their walls are too solid, not to oblige us to regard them as a kind of vesicles with tolerably thick walls. The white clear fluid (breiige) matter which they contain consists for the most part of equal-sized corpuscles, which are about as large as the blood-corpuscles—not however flat, like these, but irregularly globular. These corpuscles present exactly the same microscopic appearance, and are of the same size, as the granules of which the red substance of the spleen is composed.” Pp. 88, 89.

Although the Malpighian bodies have been the subject of frequent and repeated investigations since 1834, I think that more has been done to confuse than to improve the above (in its general outlines) very accurate account of their structure.

Giesker, in a work which I have not seen (Splenologie, 1835, cited by both Henle and Kölliker), appears to have been the first to diverge from Müller’s views. He states that there is a delicate membrane investing the proper membranes of the

Malpighian bodies in which arterioles ramify—and thus the latter never enter the Malpighian bodies at all (Henle, Allg. Anat. p. 1000) ; and Kölliker, Gerlach, and Sanders (On the Structure of the Spleen, Annals of Anat. and Phys. 1850), agree with Giesker on the latter point.

In the meanwhile, however, Günsburg (Zur Kenntniss des Milz-gewebes, Müll. Arch. 1850) had confirmed and extended Müller’s observations with regard to the distribution of the vessels in the Malpighian bodies. He says, p. 167, “Their framework is a vascular plexus. The larger vessels (cylinder) are longitudinally triated, in consequence of the regular arrangement of the nuclei upon their walls, the smaller are simple tubes.” These observations were made on persons who died of cholera.

In January, 1851, Dr. Sanders read a paper ‘ On the connexion of the minute Arterial Twigs with the Malpighian Sacculi in the Spleen,’ before the Edinburgh Physiological Society, in which he describes a peculiar method of preparation of the pig’s spleen, whereby arterial twigs may be demonstrated “passing diametrically across the area of the sacculi.” “Stains of blood also, often in linear arrangement, indicating capillaries, were seen in the interior of the sacculi.” Kölliker (‘ Mik. Anat.′ and ‘Handbuch,’ 1852), while denying the entrance of the arterial twigs into the Malpighian bodies, states that be had just succeeded in once observing a network of fine capillaries in those of a cat, and he supposes that they will hereafter be discovered in other animals. Finally, Mr. Wharton Jones speaks doubtfully of having observed a single capillary tube in the Malpighian bodies of the sheep. (On blood-corpuscle-holding cells.— Brit, and For. Med. Chir. Review, 1853). The existence of a special continuous membrane investing the Malpighian bodies is affirmed by Ecker, Gerlach, Kölliker, and Sanders. On the other hand, it is denied by Henle (Allg. Anat. 1001), and by Wharton Jones (1. c.)

With regard to the contents, Müller’s statements, as we have seen, waver. Henle, Gerlach, Kölliker, and Sanders say that they are composed of corpuscles suspended in a fluid. The quantity of the latter is however, according to Kölliker, small.

I may now proceed to communicate the results of my own observations upon the structure of the Malpighian bodies in Man, the Sheep, Pig, Rat and Kitten, and I will arrange what I have to say under the three heads of—1. The distribution of the vessels of the Malpighian bodies. 2. The structure of their substance (so-called contents), or the Malpighian pulp. 3. The structure of their peripheral portion, or so-called ‘ walls.’

In all the animals above mentioned, I find it very easy to demonstrate, in almost every case, that one or more minute arterial twigs enter and frequently subdivide in the substance of the Malpighian body, making their exit on its opposite side, to terminate, finally, by breaking up into minute branches in the pulp. Indeed, it is so easy to convince oneself of this fact, if a thin section of a fresh spleen be examined under the simple microscope, that it is difficult to understand how two opinions can exist upon the subject. The method I have adopted is simply this : to such a section I add some weak syrup, so as to retain the colouring matter in the blood-corpuscles contained in the vessels, and thus to have the advantage of a natural injection ; then, I either trace out the vessels into the Malpighian bodies with needles, under a -inch lens; or, placing a glass plate over the section, I apply a gentle and gradual pressure, just sufficient to render the bodies transparent. It is then easy, by sliding the plate with a needle, to cause the bodies to roll a little upon their axes, and thus convince oneself, by the relative positions which the vessels and the bodies assume, that the former do really pass through, and not merely over, the latter. In Plate III. (figs. 1, 2, and 7) I have represented the ordinary modes in which the arterial twigs are disposed in the Malpighian bodies of the sheep (figs. 1, 2) and of Man (fig. 7). It should be observed, however, that the Malpighian bodies have by no means always the well-marked oval outline which is here represented. On the other hand they are very frequently diffuse and irregular, sending out processes along the efferent and afferent twigs.

The application of a high power, either to the compressed Malpighian body, or to one which has been torn out with needles and its vessels isolated, fully confirms the results obtained by the previous methods. In Man, the structure of the minute arterial twigs within the bodies does not differ from that which they possess elsewhere (fig. 7). Both the transversely (smooth-muscular) and longitudinally fibrous coats are well developed, neither being in excess ; and the addition of acetic acid produces a clear line external to the former, representing the innermost portion of the tunica adventitia, which passes into, and is continuous with, the Malpighian pulp. The artery, therefore, is not only surrounded by, and in immediate contact with, the indifferent tissue of the pulp, but the latter, as Müller pointed out, is really the representative of a part of its tunica adventitia. In fact, the indifferent tissue so completely forms an integral constituent of the coat of the artery, that I could not, in any way, obtain the latter free from it.

In the Sheep, the arterial twigs have precisely the same relation to the Malpighian pulp, but the intimate structure of their walls is different, the circularly fibrous layer becoming almost obsolete, while the longitudinally fibrous coat acquires proportionally increased dimensions, and takes, at the same time, the structure of organic muscle. In the small arterial twigs of l-800th inch in diameter, represented in fig. 3, the cavity of the vessels did not occupy more than one-third of their diameter, and, like the efferent ramuscules, unless they contained blood, they resembled mere trabeculæ, consisting of organic muscle.

The vessels within the Malpighian bodies are, however, not arterial ramifications only : I find that there invariably exists, in addition, a tolerably rich network of capillaries connecting the arterial ramuscules. These capillaries are vessels of l-1000th to l-3000th of an inch, or even less, in diameter, which can hardly be said to have parietes distinct from the surrounding indifferent tissue of the pulp (figs. 3 and 8) ; unless they are filled with blood, indeed, they are not distinguishable with certainty ; and in the figures 2 and 7, I have, therefore, only represented those fragments of the capillary network in which blood corpuscles were clearly distinguishable, their colouring matter being retained by the syrup. After the addition of water, it is often impossible to recognize the capillaries at all ; but using syrup, I have readily enough seen them in all the animals above mentioned.

It may then perhaps be fairly concluded that, in mammals, the Malpighian bodies are traversed by minute arteries, and contain, in addition, a network of capillaries.

Almost all writers have agreed in stating that the interior of the Malpighian bodies is filled by a liquid, consisting, as Kölliker says, of a small quantity of fluid with a large proportion of corpuscles. However, I have been quite unable to convince myself of the existence of any fluid matter at all in the interior of the perfectly-fresh Malpighian bodies of any of the animals I have examined. On the other hand, the Malpighian pulp appears to me to be as solid as any other indifferent tissue, e. g., that which constitutes the lowest layer of an epidermis or epithelium, or as the most superficial portion of any dermal structure. It is, indeed, like these, soft and capable of being crushed into a semifluid substance, which becomes diffused in any surrounding liquid, like mud in water ; but that it is a soft solid and not a fluid, results, I think, from what I have stated with regard to the difficulty of completely detaching it from the arterial twigs.

The essential structure of the Malpighian pulp appears to me to be that of every other indifferent tissue which I have yet examined ; it consists, in fact, of a homogeneous, transparent, structureless matrix, or periplast, containing closely-set rounded or polygonal vesicular endoplasts : these vary in diameter from less than 1-5000th inch up to l-2500th, or a little more, and contain usually one to three, but frequently many, minute granules* (fig. 4). On the addition of acetic acid, the periplast often becomes granular and less transparent, while the endoplasts are rendered darker and more sharply defined, undergoing a certain wrinkling. There are neither cell cavities nor cell walls distinguishable around these endoplasts, and therefore the Malpighian pulp cannot be said to be composed of ‘ nucleated cells resembling, in this respect, all the primary, unmetamorphosed tissues with which I am acquainted.

True cells are, however, to be met with here and there in the Malpighian pulp. There is first to be observed a clear area, as of a cavity, surrounding an endoplast ; the periplast forming the outer limit of this clear area then acquires a more distinct definition (fig. 5), and becomes recognizable as a cell-wall, from the remaining periplast. Such complete cells measure from l-2500th to l-1500 th of an inch in diameter. A further change is undergone by the periplast within and around some of these cells ; granules are deposited, which are sometimes minute and colourless, sometimes, on the other hand, have a deep-red colour and a considerable size, constituting the well-known ‘ pigment-globule-cells’ of the spleen ; but I may remark, that I have never been able to observe any blood corpuscles in such cells.

If the Malpighian pulp be pressed out or torn with needles, it is very readily broken up and diffused through the surrounding fluid. We then find in the latter free endoplasts—endoplasts surrounded by definite cell walls and cell cavities—and granule and pigment cells, corresponding with the elements which were observed in the uninjured tissue. That the free cells were not primarily independent structures, but have simply resulted from the breaking up of the periplast along its lines of least cohesion, is evidenced, in a very interesting manner, by such forms as are represented in fig. 6, where two cells may be observed still connected by a bridge of periplastic (or as it would here be called, in the language of the cell theory, ‘intercellular’) substance, while the outline of a single isolated cell is still irregular and granular, from the adhesion of particles of the periplast of which it once formed a portion. Such bodies as these are quite undistinguishable, structurally, from pus, mucus, or colourless blood corpuscles *.

In the human spleen, the Malpighian bodies cannot be said with any propriety to possess walls. Their structure remains, as we have described it, up to their junction with the surrounding red pulp. At the line of junction, a somewhat more condensed tissue, which breaks up, like a great deal of the red pulp, into spindle-shaped bodies, and those fibres with one-sided endoplasts, described by Kölliker, may be found ; but this tissue belongs as much to the red pulp as to the Malpighian body.

In the Sheep, on the other hand, I find, to quote Mr. Wharton Jones’s words, that— “Examined with a low magnifying power, the Malpighian cor-vesicles present the appearance of thick-walled, glandular vesicles, with contents. The thick walls are not defined and homogeneous, but are, on examination with a high power, found to be composed of nucleated fibres and nucleated corpuscles, similar to those of the red pulpy substance, between which, indeed, and the exterior surface of the Malpighian corpuscles there is no very distinct line of demarcation other than is produced by the condensation of the wall of the Malpighian corpuscles and the absence in them of coloration.”

In addition to this, however, I find upon the exterior of the Malpighian bodies in the Sheep the mesh-work of pale fibres, (fig. 2, d,) like very young elastic tissue, or the fibres of the zonule of zinn, to which Kölliker and Sanders have referred ; and I have occasionally met with such fibres in the interior of the bodies themselves, traversing the Malpighian pulp. They appear to me to belong to the original tunica adventitia of the arteries. The existence of any distinct structureless limitary membrane may, I think, be very decidedly denied ; and with regard to the “granular membrane, the internal surface of which is lined by a layer of large nucleated cells, while free nuclei or corpuscles, with a homogeneous or granular plasma, fill its interior” (Sanders, 1. c., p. 35) ; all I can say is, that I cannot give any opinion as to what it may be, never having met with a Malpighian body presenting any such structures.

It may be said, then, that the Malpighian bodies of the mammalian spleen are not closed follicles, and have no analogy whatever to the acini of ordinary glands, but that they are portions of the spleen, everywhere continuous with the rest, but distinguished from it—a, by immediately surrounding, and as it were replacing, the tunica adventitia of the arteries ; b, by containing no wide venous sinuses, but, at most, a network of delicate capillaries ; and c, by being composed of absolutely indifferent tissue, i. e. of a structureless periplast with imbedded endoplasts—or of a tissue in which the periplast has undergone no further metamorphosis than that into cellwall and rudimentary fibre.

For a demonstration that each of these propositions holds good of the Malpighian bodies in the other three classes of the Vertebrata, I must refer to Remak’s very able essay, ‘ Ueber Pigment-kugel-hâltige Zellen,’ in Müller’s ‘ Archiv.’ for 1852, and to Leydig’s recent ‘ Untersuchungen über Fische und Reptilien,’ in which ample evidence of the fact will be found ; and my limits oblige me to allude, with equal brevity, to another important doctrine which many recent writers have maintained, but which is especially enunciated and illustrated by Leydig, namely—that there is no line of demarcation to be drawn between the spleen, the lymphatic glands, Payer’s patches, and the glandulæ solitariæ, the supra-renal capsules, the thymus, and the pituitary body, but that these form one great class of glands characterized essentially by being masses of indifferent tissue contained in vascular plexuses, and which may therefore well retain their old name of Vascular Glands.

The primary form of these is represented by the solitary gland of the alimentary canal, which is nothing but a local hypertrophy of the indifferent element of the connective tissue of the part, and possesses no other capsule than that which necessarily results from its being surrounded by the latter.

A number of such bodies as these, in contiguity, constitute, if they be developed within a mucous membrane, a Payer’s patch ; if within the walls of the splenic artery and its ramifications, a spleen ; if within the walls of lymphatics, a lymphatic gland ; if in the neighbourhood or within the substance (as in Fishes) of the kidney, a supra-renal body ; if in relation with a part of the brain, a pituitary body* All these organs agree in possessing nothing that can be called a duct. To those, however, which are in relation with mucous membranes, Kölliker has already justly shown (‘Handbuch’ and ‘ Mikr. Anat.’) that the ‘ follicular’ glands of the root of the tongue and the tonsils must be added ; the former of which possess rudimentary, and the latter a tolerably perfect, system of ducts, formed by diverticula of the mucous membrane, around which the elements of the vascular gland are arranged, though they are not directly connected with them. I can fully testify to the general accuracy of Kölliker’s account of the structure of the tonsils ; but I must add that I have been unable to find ‘ closed follicles’ either in Man or in the Sheep; and, on the other hand, that the indifferent tissue of the so-called ‘ follicles’ is permeated by a network of capillaries, which have exactly the same relation to the indifferent tissue in which they are imbedded, as in the Malpighian bodies (figs. 9, 10). So far as its structure is concerned, in fact, the tonsil exactly represents a lymphatic gland, developed around a diverticulum of the pharyngeal mucous membrane ; its ‘ follicles’ precisely resembling the ‘ alvcoli’ of the latter, in being constituted by imperfect septa of rudimentary connective tissue, containing a solid mass of indifferent tissue, traversed by capillaries.

Can this series of ‘ vascular glands with false ducts,’ as they might be called, be extended by any further addition ? I venture to think that it may, and that no one can thoroughly comprehend the structure of the tonsils without perceiving, at once, that there is but a step from them to the liver. A mass of indifferent tissue contained in a vascular plexus and arranged around a diverticulum of mucous membrane, is a definition which would serve as well for the liver as for the tonsil ; it is, further, perfectly in accordance with that theory of the relation of the biliary ducts to the hepatic substance, which is due to Dr. Handfield Jones, and which all recent researches, both anatomical and physiological, tend to confirm, viz., that the liver is essentially a double organ, consisting of two elements, an excretory and a parenchymatous, different homologically and functionally. It seems odd that, from being a sort of histological and physiological outcasts, the Vascular Glands should turn out, if this view be correct, to be the most important and extensive class of organs in the whole body, claiming the gland par excellence, the liver—as one of their family.

*

These therefore correspond with the “nuclei” and “nucleoli” of authors. The reasons for not so denominating them are contained in an article ‘ On the Cell Theory’ (‘Brit, and For. Med. Chir. Review, October 1853’). I may observe that I know of no tissue better calculated to illustrate the view which I have there taken of Histogenesis, than the Malpighian pulp.

*

The above account of the structure of the Malpighian bodies is essentially identical with that given by Mr. Wharton Jones, 1. c. pp. 34, 35, but was drawn up before I had the good fortune to become acquainted with his article. He describes the wall of the nucleated cells as being “not very smooth,” and the periplast as a “diffluent intercellular substance,” whence 1 presume that I may quote him as an authority for the absence of fluid in the Malpigbian bodies.

*

I purposely abstain from including in this series the thyroid and pineal glands, because I think it certain that the former, and probably, the latter, have a different import.