The following may be noticed concerning the microscropic structure of the splenic vessels : —The arteries everywhere possess their three usual coats. The inner consists, first, of an epithelium of spindle-shaped cells, which easily come off' in skeins or separately (fig, 535, a,b); and, secondly, of an elastic mem brane of homogeneous composition, wrinkled in the longitudinal direction (fig. 528, e.), and with or without openings : which openings although very small, are visible even in the arteries of the tufts. The middle tunic is very thick, and gives rise to the considerable thickness of the wall of the vessel ; it con tains very little else but unstriped muscular fibres, In the larger and largest arteries, nets of elastic fibre and elastic membrane (geftnstirte membranen of Henle) are also present, while they exist without exception on the vessels which pass to the Malpighian corpuscles, and on those which form the pencils or tufts. The adventitious (or cellu lar) coat is altogether absent from the smaller vessels in the interior of the spleen, and is here represented by the sheath ; hut it exists in the larger vessels, and presents white fibrous tissue and meshes of elastic fibres.
The capillaries (fig. 536.) have"a simple, tureless membrane, with nuclei lying on its inner surface. The veins have been already described as they exist in brute mammalia : in man they possess-1. An epithelium as above described ; 2. A membrane of elastic longi tudinal fibres ; 3. Transverse unstriped mus cular fibres, in a single or double layer, which are present in the trunk of the splenic vein and all its primary branches in the interior of the spleen, but are absent from the smaller and smallest veins ; 4. White fibrous tissue, with elastic fibres which take a longitudinal direction. The smallest veins possess only white fibrous tissue with elastic fibres, and an epithelium.
So much has been already said above con cerning the blood of the splenic vessels and of .the spleen, that I will here only- append some "special observations made upon animals. In a dog whose spleen abounded in the dissolv ing blood globules, the blood of the splenic vein distinguished itself by a very great quan tity of colourless blood corpuscles, almost all of which contained numerous nuclei, and often had a deceptive resemblance to pus globules. In the blood of the liver were found a great number of altogether different blood globuleslfig. 537.). These were swollen out and almost colorless, but contained from 1 to 5 thinner or thicker small rods of a dark yellow colour ; part of these possessed the same length as the blood globules, part were shorter. These small rods were unchanged in water, but in acetic acid they seemed to disappear. In a second dog I found the same cells with small yellow rods in the blood of the splenic vein, while they could not be detected in any other part of the body. With them I found at the same time numer ous colourless blood globules with manifold nuclei. In the fresh-water perch, the blood of the splenic vein of many individuals con tained numerous golden yellow cells with diminished blood globules. In the same blood, and in the splenic pulp, there also occurred, either sparingly or in uncommon quantity, rod-shaped crystalline corpuscles, of a yellow colour, and a length of 4 to 6-1000ths of a line : at the first glance they seemed to be lying altogether free, and they were dissolved by potash (fig. 638, b). On the application of water a membrane was upraised from these small rods, and near them a nucleus came into view (fig. 538, rz). On more accurate in
quiry, it plainly appeared that these small rods lie in decolorized blood globules, and in unchanged blood globules the gradual form ation of one, or even two, of these may be followed. In Barbus .fluviatilis, the spleen pulp contains an enormous quantity of really free crystals; these are of a violet and reddish colour, and of a nail or spindle-shaped form ; and on the application of acetic acid, they are completely dissolved, leaving some colour behind. Crystals such as these also occurred sparingly in the kidneys, the liver, and the blood of the heart. In this animal, as well as in Ojprinus brama, the blood contained yellow granule-cells, like those which occur in the spleen and kidneys. All the rod-shaped yellow corpuscles just named (of which the first, indeed, are nothing but crystals) must in any case consist of a substance allied to the hcematin of the blood ; and possibly they consist of the substance which Virchow has lately named hmatoidin, with which they correspond in some respects. Their occur rence in the spleen is physiologically inter esting, and so also is their formation within the blood corpuscles, while at the same time it affords a very plain indication of the rela tion of hmmatin to them.
7. Lymphatics.— The views of authors con cerning the lymphatics of the spleen are very contradictory, since one class have the prece dent of Haller for altogether denying their existence in the human spleen, while others have stated their existence in abundance, and have constituted the spleen, in a certain mea sure, a large lymphatic ganglion. This differ ence mainly depends hereon,—that the one class have specially examined the human spleen,whi I e others have chiefly drawn their conclusions from that of the lower animals, considerable differences in respect of these vessels existing in different creatures. In man, the lymphatics of the spleen are, at any rate, in utterly in considerable quantity, being rather less nu merous than in other glandular organs, as the liver and kidneys, and not at all so numerous as in the lymphatic glands. They are divi sible into superficial and deep. The former course, in sparing numbers, between the two coats of the spleen, and form in this situation delicate trunks, which anastomose with each other ; but, excepting in perfectly healthy spleens, and in the neighbourhood of the hilus, they can scarcely be recognised. The latter lie in sparing numbers in the hilus, and in the sheaths of the vessels, where they accompany the arteries, although they cannot be traced so far as there. Both sets of these vessels pass to the gastro-splenic omentum, to enter the small lymphatic glands placed there ; and finally they collect to a trunk which opens into the thoracic duct, at about the eleventh or twelfth dorsal vertebra. All these lymph atic vessels can only be thus seen in the quite fresh and undeteriorated spleens of executed criminals or subjects killed by accidents, al though they may often be recognised in parti cular parts of the healthy spleen after natural death, especially if the vessels be tied and the spleen soaked in water. But, on the other hand, in diseased spleens it is very rare to see even a trace of them, unless a preparation be made of a small gland in the gastro-splenic ligament, in which case small entering and emerging trunks may be recognised.