CH. XXni.] THE SPLEEN 331 



are also large cells containing either a pigment allied to the colouring 

 matter of the blood, or rounded corpuscles like red corpuscles. 



The splenic artery, after entering the spleen by its concave surface, 

 divides and subdivides, with but little anastomosis between its 

 branches; at the same time its branches are sheathed by the pro- 

 longations of the fibrous coat, which they, so to speak, carry into 

 the spleen with them. The arteries soon leave the trabeculse, and 

 their outer coat is then replaced by one of lymphoid tissue; they 

 end in an open brush-work of capillaries, the endothelial cells of 

 which become continuous with those of the rete of the spleen-pulp. 

 The veins begin by a similar open set of capillaries from the large 

 blood spaces of the pulp. The veins soon pass into the trabeculae, 

 and ultimately unite to form the splenic vein. This arrangement 

 readily allows lymphoid and other corpuscles 

 to be swept into the blood -current. 



On the face of a section of the spleen can 

 be usually seen readily with the naked eye, 

 minute, scattered, rounded or oval whitish 

 spots, mostly from ^V to ^V i ncn (f to f mm.) 

 in diameter. These are the Malpighian cor- 

 puscles of the spleen, and are situated on the 

 sheaths of the minute splenic arteries. They 

 are in fact outgrowths of the outer coat of 



T i i ., t> f n nr\n\ FIG. 310. Reticulum of the 



lymphoid tissue just referred to (see fig. 309). spieenofacat.shownby 

 Blood capillaries traverse the Malpighian cor- {gSjg} with gelatine - 

 puscles and form a plexus in their interior. 

 The structure of a Malpighian corpuscle of the spleen is practically 

 identical with that of a lymphoid nodule. 



The spleen has the following functions : 



(1.) The spleen, like the lymphatic glands, is engaged in the 

 formation of colourless Hood-corpuscles. For it is quite certain, that 

 the blood of the splenic vein contains an unusually large proportion 

 of white corpuscles; and in the disease termed leucocythoemia, in 

 which the white corpuscles of the blood are remarkably increased in 

 number, there is found a hypertrophied condition of the spleen, 

 especially of the Malpighian corpuscles. The white corpuscles 

 formed in the spleen also doubtless partly leave that organ by 

 lymphatic vessels. 



By stimulating the spleen to contract in a case of splenic 

 leucocythaemia by means of an electric current applied over it through 

 the skin, the number of leucocytes in the blood is almost immediately 

 increased. 



Kemoval of the spleen is not fatal ; but after its removal there is 

 an overgrowth of the lymphatic glands to make up for its absence. 



(2.) It forms coloured corpuscles, at any rate, in some animals ; in 



