SPLEEN (Lat. splcn, from Gk. awX4v, spleen; connected with Lat. Hen, Skt. plihnn, spleen). The largest and most important of the so-called ductless glands. It is generally oval in form, somewhat concavo-convex, soft, of very brittle consistence, highly vascular, of a dark bluish-red color, and situated in the left hypochondriac region, with its interior slightly concave surface embracing the cardiac end of the stomach and the tail of the pancreas. In the adult it is usu ally about 5 inches in length, 3 or 4 in breadth, and an inch or an inch and a half in thickness, and weighs about 7 ounces. At birth its weight in proportion to that of the entire body is as I to 350, which is nearly the same ratio as in the adult ; while in old age the organ decreases in weight, the ratio being as 1 to 700. The size of the spleen is increased after gastric digestion, and is large in highly fed and small in starved animals. In intermittent fevers and leneocythag mia it is much enlarged, weighing occasionally from IS to *20 pounds, and constituting what is popularly known as the ague-cake.
The spleen is invested externally by the peri toneum and inside this by a fibrous capsule giving off from its inner surface numerous small fibrous bands termed trabeculw, which unite at numerous points with one another, and run in all directions. The parenchyma or proper substance of the spleen occupies the interspaces of the above-described areolar framework, and is a soft pulpy mass of a dark reddish-brown color, con sisting of colorless and colored elements. The colorless elements consist of granular matter, of nuclei about the size of the red blood-disks, and a few nucleated vesicles, and constitute one half or two-thirds of the whole substance of the pulp in well-nourished animals, while they dimin ish in number, and sometimes altogether disap pear, in starved animals. The colored elements consist of red blood-disks and of colored cor puscles either free or included in cells; some times enlarged blood-disks are seen included in a cell. but more frequently the inclosed disks
are altered in form and color, as if undergoing retrograde metamorphoses. Besides these, nut mesons deep-red, or reddish-yellow, or black cor puscles and crystals, closely allied to the ls:ema tin of the blood, are seen diffused through the pulp substance.
The venous blood of the spleen is carried away by the splenic vein, which contributes to form the great portal venous system, distributed through the liver; While arterial blood is sup plied by the splenie artery. the largest branch of the creliac axis. The branches of this artery subdivide and ramify like the brandies of a tree, with the Malpighian or splenie corpuscles at tacked to them like fruit. These splenie cor puscles. originally discovered by Malpighi, are whitish spherical bodies, which are either con nected with • the smaller arterial branches by short pellicles, or are sessile upon their sheaths. They vary considerably in size and number, their diameter usually ranging from 1-30 to 1-60 of an inch. Each consists of a membranous capsule, homogeneous in structure, and formed by a pro longation from the sheath of the artery. The blood capillaries form a delicate plexus within these corpuscles.
With regard to its uses the spleen may be re garded as a storehouse of nutritive material, which may be drawn upon according to the re quirements of the system, and the constant pres ence in large amounts of certain nitrogenous substances seems to indicate that some special nitrogenous metabolism takes place in it. The formation of both white and red blood cells probably also occurs in the spleen as well as the disintegration of exhausted blood corpuscles.