In conclusion, one word concerning the import of the changes of the blood corpuscles in the spleen. It may be asked, whether they constitute a normal and physiological, or a pathological appearance ? On the one side, very weighty grounds may be alleged for the normal character, especially their (so to speak) constant occurrence and innumerable quantity in such a number of animals living in their natural condition, as the amphibia and fishes were. Furthermore, the appa rently complete health which existed in spite of the vast quantity of dissolving blood globules. Thirdly, in Reptilia, the cells con taining blood corpuscles may be seen in blood vessels which are in no way isolated from the general circulation. Fourthly, similar and constant changes of the blood repeated at short intervals are absent from other organs of birds, mammals, and reptiles ; and many other arguments might be adduced. But, in contrast to these facts, many others appear on a more careful contemplation, which may almost lead to the opinion that all the changes of the blood globules in the spleen are pos sibly only pathological appearances. In fishes, dissolutions of the blood corpuscles occur not only in the spleen, but in an exactly similar way in other organs, namely in the kidney-s, the liver, and the peritoneum. In the first of these organs their presence is constant ; at least, in the examination of many examples of eel, pike, Coregonus murwria and murmnula, Salmo fario, Barbus fluviatilis, Cyprinus brama and carpio, and Tinca chrysitis, not only- were they always present, but almost always as numerous as they were observed to be in the spleen. In the peritoneum and the liver they were sometimes scarce, sometimes frequent, but only in the carp and Tinca chrysitis were they constant ; in other fishes they were either altogether absent, or only occurred here and there, as in the trout. If to these facts be appended that in certain animals,—to wit, in cats, sheep, and others,— the changes of the blood corpuscles in the spleen are very seldom observed, one can scarcely resist the notion that the appearance is abnormal ; and this is much more the case when one con siders that similar appearances which are known not to be physiological, constitute almost constant occurrences, and are asso ciated with exactly parallel changes of blood globules. Of this, the small effusions of blood in the lungs, bronchial glands, and thyroid bodies of men, and those of the lymphatic glands and mesentery of pigs and rabbits, are instances. But this latter view is insusceptible of full explanation ; for although pathological effusions and metamorphoses of blood often constitute almost a constant oc curence, yet, first, the quantity of blood globules which undergo dissolution in such effusions is in no comparison at all with that of the millions which are destroyed in the spleen ; and, secondly, it has yet to be shown that effusions of blood may not occur as a physiological phenomenon, as happens in the bursting of a Graafian follicle in the ovary, in menstruation, and in the separation of the placenta. And although all animals do not show in the spleen such a solution of the blood corpuscles as can be verified by the microscope, yet it is by no means proved therewith, that where this takes place it de pends on a pathological condition ; indeed, the blood corpuscles of different animals may undergo dissolution in different ways. At least thus much is certain, that in all animals, without exception, stagnations of blood occur in the spleen; and I might add, almost of a certainty, in mammals, extravasations also. In these stagnations, the blood globules may dissolve themselves in the one case rapidly, in the other case slowly, and thus, according to the outer phenomenon, a diference will be produced. Such an occurrence may be phy siological, since it is, at least in many animals, visibly constant and very extensive ; and it rnay have the greatest signification to the life of the organism. Therefore, so long as the pathological character of the phenornenonis not proved of a certainty, I am disposed to hold fast by its physiological nature, and to consider the dissolution of the blood cor puscles in the spleen as a normal fact.
6. Bloodvessels of the spleen.— The spknie artery (arteria lienalis) springs from the cmliac axis, and courses with many windings between the layers of the gastro-colic liga ment until it reaches the fundus of the stomach, where it enters the gastro-splenic ligament, after giving off some small twigs to the pancreas and the stomach. Arriving in the neighbourhood of the hilus lienalis, it divides into a superior and an inferior branch. The upper of the two, passing somewhat upwards, and giving backwards from two to six short arteries (vasa brevia) to the large extremity or pouch of the stomach, divides into from three to six branches, which, lying in a line one over another, extend to the haus, into which they enter. The inferior branch is somewhat larger than the others ; it passses to the in ferior and anterior part of the spleen, sup plying it with three to six branches, which enter the hilus in the same manner as the others, and it ends finally as the gastro epiploica sinistra. Thus, all the six to twelve branches which enter the spleen lie tolerablv in one line upon each other in the gastro splenic omentum, and they are also connected to each other by fat and areolar tissue. The size of the splenic arteries is very consi derable in proportion to that of the organ, and so also the thickness of their coats is worthy of notice. In the first of these re spects, it is possible that only the thyroid gland exceeds the spleen ; the liver, which is so much larger than this organ, being sup plied by an artery of scarcely larger size than the splenic, although we must not over look the fact, that beside this the liver receives very much additional blood through the vena portm. In the mammalia generally, the splenic artery is proportionally smaller than in men ; this possibly depends only upon the more considerable contraction of the vessel at their death. Wintringham finds that the thickness of the arterial coats is greater than that of the aorta above the giving off of the renal ar teries, to which it bears the ratio of 1 to 0.762 ; he also states that they will sustain a pres sure of 41 lbs.
The serous covering of the spleen receives some unnamed small arteries : thus a twig is given to it from the left inferior phrenic artery, which courses in the phrenico-lienal ligament ; and, besides this, it receives branches from the first lumbar, from the left spermatic, and from the splenic itself'. Addi tionally to these, in some of the vertebrate, to wit in the calf, stnall twigs in great number leave the substance of the spleen, and after perforating the fibrous coat of the organ spread themselves out upon its surface.
The splenic vein altogether corresponds in distribution to the splenic artery. So niany primary arterial branches enter the hilus of the spleen, and just as many veins come out of it. These six to twelve veins unite into two branches, and receiving, the upper the venue breves from the stomach, and the lower the vena gastro-epiploica sinistra, they constitute the trunk of the vein. In the spleen, and at their emergence from it, the veins lie anterior to the arteries, but then they place themselves posteriorly to them ; and it is behind the arteries that they unite to form the common trunk. This trunk receives a twig from the pancreas, from the lymphatics of the spleen, from the stomach, and, further, the vena coro naria ventriculi ; it then passes away over the aorta to the under surface of the liver ; and, finally, with the vena mesenteries superior it constitutes the trunk of the vena port.
The splenic vein, like all the branches of the vena portw, has no valves, and is the largest branch which assists to form that trunk. Its width is very considerable : ac cording to E.FIome* and Giesker, the propor tion to that of the arteries is as 5 to I ; and according to earlier authorities it is yet more. The proportionate size of the branches is still larger ; and, according to C. A. Schmidt, their ratio in the spleen itself to that of the arteries which run with them is as 20 to 1. In con trast to this, the thickness of their coats is very inconsiderable, and, according to Win tringham, is to that of the arteries as 1 to 4'8 or 423, to that of the iliac vein as 1 to :3-5.