Anat.,' II, 2; and Todd's 'Cyclopædia of Anatomy and Physiology,' Art. Spleen, fig. 533; Ecker, 'Icon. Phys.,' tab. vi, figs. 15, 16); 2. extravasations and metamorphoses of their blood-corpuscles occur, not only in the spleen, but in other organs, especially in the kidneys, where they are constant, and frequently also in the liver and peritoneum.

If to these facts we also add, that in certain animals, e. g. the Cat, the Sheep, &c., the changes of the blood-corpuscles in the spleen are very rarely met with-furthermore, that their progress is not always coincident with the stages of digestion -it becomes very difficult not to believe that the phenomena are abnormal, especially if we consider that similar phenomena certainly not physiological, such as the small effusions of blood into the lungs, bronchial glands and thyroid in Man, in the lymphatic glands of the mesentery of the Pig and Rabbit, &c., are also, on the one hand, almost as constant phenomena, and, on the other hand, are accompanied by perfectly similar metamorphoses of the blood-corpuscles. However, in the latter cases, the quantity of the metamorphosed blood-corpuscles is not to be compared to the immense number of those which are constantly undergoing disintegration in the spleen; and in the second place, it is also possible that effusion of blood may occur as a physiological phenomenon, as into the Graaffian follicles, and during menstruation and the detachment of the placenta. And although all animals do not present a microscopically demonstrable disintegration of the blood-corpuscles in their spleen, yet it does not follow that the process may not occur and that when it can actually be demonstrated, it is pathological. This much is at least certain, that congestions of blood in the spleen occur in all animals, without exception; and it is almost certain, that these congestions are, in Mammals, attended by extravasation. In these stagnations of blood, the blood-corpuscles may be disintegrated, in some cases rapidly, in others slowly, which would constitute an important difference for the observer; it is also conceivable that they and their consequences are physiological and have some great influence upon life, since it is a fact, that in many animals they are constant, and occur upon a very large scale.

For the present, therefore, so long as the pathological character of the phenomena in question is not conclusively

demonstrated, I must maintain their physiological nature and regard the disintegration of blood-corpusles in the spleen as a normal occurrence.1]

§ 169.

Vessels and nerves. As they enter the organ, the relatively very large splenic artery and the still larger splenic vein, are accompanied by those processes of the fibrous membrane, which have been referred to as the vascular sheaths. In Man these processes form complete investments around the vessels and nerves, somewhat after the fashion of the capsule of Glisson, so that the arteries and nerves especially, can be readily isolated, while the veins, which on the side opposite to the artery are more intimately connected with the sheath, are less easily se

[With respect to the "blood corpuscle-holding cells," the reader will do well to consult Remak's very valuable and elaborate paper, 'Ueber runde Blutgerinnsel und über Pigment kugel haltige Zellen,' in Müller's Archiv,' for 1852, and Mr. Wharton Jones's article on the same subject in the British and Foreign Med. Chir. Review,' for 1853, to which we have already referred. Having carefully studied them, he will, we think, arrive very much at our own conclusion, that as the question now stands, the very existence of "blood corpuscle-holding cells" must be considered as highly problematical.

Mr. Wharton Jones found the blood of the splenic vein to contain nucleated corpuscles and fibres identical with those of the pulp, together with free nuclei similar to those of the nucleated corpuscles; on the occurrence of which, he considers the statements as to the abundance of colourless corpuscles in the blood of the splenic vein are founded. Some of these elements were traced as far as the vena portæ, but in the hepatic veins they had mostly, though not entirely, disappeared. He appears to be inclined to draw the conclusion that some of the venous radicles of the spleen are connected with the pulp in the same way as the hepatic ducts with the parenchyma of the liver, and that the materials thus derived by the blood from the spleen may concur in fitting it for the secretion of bile. Moleschott (Ueber die Entwickelung der Blutkörperchen,' Müller's 'Archiv,' 1853) gives some curious results obtained by extirpating the liver and spleen of Frogs. Normally, the cardiac blood of Frogs contains about 8 red corpuscles to 1 colourless; after extirpation of the liver, the proportion is 2-3 red corpuscles to 1 colourless. The blood of the spleen of Frogs contains, normally, six times fewer red corpuscles in proportion to 1 white, than that of the heart. After extirpation of the liver, there are 1-6 colourless corpuscles to 1 red corpuscle in the splenic blood. When the spleen alone has been extirpated, the proportion of red corpuscles is slightly increased. Moleschott concludes that the liver favours the metamorphosis of colourless into red corpuscles. However, we must confess that the results of the individual experiments, from the average of which his conclusions are drawn, vary so widely as to throw some doubt on the latter.-EDS.]

parable. At first the sheaths are as thick as the fibrous coat itself and they retain this thickness so long as they surround the principal branches of the vessels. The finer ramifications of the latter and even those small branches which are given off from the large ones, have finer and finer sheaths, until at last, when the vessels are quite minute, they become lost as thin membranes in the pulp. The thickness of any sheath is always less than that of the wall of the artery to which it belongs and greater than that of the vein, but after division. the sheaths become relatively stronger. It was remarked above, that a number of the trabeculæ are inserted into the vascular sheaths and they therefore take a share, together with the vessels which they inclose, in the formation of the dense network in the interior of the spleen. In Mammalia, as in the Horse, Ass, Ox, Pig, Sheep, &c., the sheaths present different relations, inasmuch as the smaller veins have none at all, and the larger possess them only on the side on which the arteries and nerves lie. Only the two principal venous trunks near the hilus have perfect sheaths, whilst the arteries, from the main trunks to the finest ramifications, all possess them. The structure of the sheaths is precisely that of the trabecule, but muscles are not always found in the former when they are contained in the latter-e. g. in the Ox-while in the Pig they are also very distinct in the sheaths.

The splenic artery, immediately it enters the organ, and all its principal branches, divide and spread out into a great number of ramifications, the larger of which proceed towards the anterior margin of the organ, the smaller towards the posterior, forming no anastomoses with those of other principal branches. When they have diminished to the diameter of, they separate from the veins, which till then had run in the same sheath with them, and become connected by branches of 001-002", with the Malpighian corpuscles in the manner which has been described above; perhaps, also, sending fine branches into their interior (see § 167). Then, often closely applied to the surface of the corpuscles, but, so far as I can observe, not passing through them, as Joh. Müller formerly supposed, they enter the red pulp and immediately break up into elegant bundles of minute arteries, the so-called penicilli (fig. 232), which finally subdivide into true capillaries

of 0.003-0.005", which throughout the pulp, round the Malpighian corpuscles, as well as elsewhere, unite into a somewhat wider network.

Fig. 232.

With respect to the veins, I must especially express myself against the existence of the venous sinuses or spaces of ancient and modern anatomists, in the human spleen. The larger veins which still accompany arteries, present no peculiarities, except in their width; all possess a membrane, which is, at least upon the side of the artery, easy of demonstration, and, like the vascular sheath, gradually becomes thinner. Apertures of more minute veins, the so-called stigmata Malpighii, exist only in inconsiderable numbers in the largest of these veins, while in the smaller, they are more frequent. From the point of divarication of the arteries and veins, the relations of the latter become somewhat different. In the first place, they give off upon all sides a vast number of small veins, usually at right angles, whence their walls appear in places almost cribriform; and secondly, their membranes become completely coalescent with the sheaths of the vessels, so that ultimately the two constitute only a single very delicate wall, which, however, may

Fig. 232. An artery with its penicillate ends, from the spleen of the Pig, × 25.

still be easily detected in the very smallest vessels that can be be isolated by dissection. I find dilatations of any kind in no part of these veins, only, it is to be observed that they become narrowed more slowly than the arteries. Their continuity with the capillaries takes place in exactly the same manner as in all other organs and may be demonstrated without difficulty, by injecting the veins of a well preserved human spleen, especially of a child. Neither does any trace of dilatations present itself in this case.

The capillaries of the spleen have the ordinary structure, and a width of 0.003""-0.005""; they are very numerous, and exist throughout the pulp, where, round the Malpighian corpuscles, though not in their coats, and elsewhere, they form a tolerably close network continuous through the whole spleen, only interrupted by the minutest trabecule and by the Malpighian corpuscles.

The human spleen possesses, relatively, very few lymphatics. The superficial set are distributed sparingly between the two coats, but can hardly be recognised, except in the neighbourhood of the hilus and in perfectly healthy spleens. The deep set may be discovered in the hilus, whence also, few in number and small in diameter, they accompany the arteries, but cannot be traced by any means so far as these. In the hilus both sets of lymphatics join, traverse a few small glands, which exist in this locality, and finally unite into a trunk which opens into the thoracic duct opposite the 11th or 12th dorsal vertebra. In diseased spleens no trace of the superficial lymphatics can ordinarily be detected.

The nerves of the spleen, consisting of many fine and a few thick tubules, with a moderate proportion of Remak's fibres, are derived from the splenic plexus, formed by two or three trunks which surround the splenic artery, and are continued on the arteries into the interior of the organ, each dividing into one or two branches, anastomosing here and there. In the Sheep and Ox, these splenic nerves are truly colossal, so that, taken together, they equal the empty and collapsed splenic artery, this size, however, being attributable principally to the unusual quantity of Remak's fibres.

In animals, these nerves, which never possess ganglia, may be followed into the spleen further than in Man; and, by the aid of the microscope, I have frequently met with them even