THE SPLEEN. 



405 



adenoid tissue ; the fibrillse become more delicate and interlace 

 in a coarser meshwork ; in the interstices are lymph-cells and 

 at the nodal points are small nuclei. Klein describes large, flat- 

 tened endothelioid cells, " endothelioid plates," fixed upon the 

 reticulum. This lymphoid tissue surrounds the artery in a 

 loose coat of variable thickness. At certain points there is a 

 local hyperplasia of it ; it becomes massed into little ovoid or 

 spherical bodies, which are called Malpighian corpuscles. 

 These have a diameter of T V to T V mm. They are attached 

 like buds to the artery, or, not rarely, the artery pierces them 

 centrally or eccentrically. When thus pierced the lymphoid 

 change in the arterial coats extends much deeper. The cor- 

 puscles resemble very closely the follicles in the solitary glands 

 of the intestine, as well 

 as those of the lymphatic 

 glands (Fig. 173). They 

 are composed of the same 

 retiform connective tis- 

 sue, in the meshes of 

 which are lymphoid cells, 

 with occasionally yellow 

 or brown pigment. This 

 retiform tissue becomes 

 denser near the external 

 part of the corpuscle, 

 but no distinct envelop- 

 ing membrane exists. In- 

 deed, the external sur- 

 face is generally connect- 

 ed by fibrillse with the 

 branching cells of the spleen-pulp surrounding it. Toward 

 the centre the retiform tissue is more open. The cells within 

 the meshes are lymph-cells of various sizes. They have an 

 average diameter of T J mm. The smaller ones have a single 

 nucleus, the larger may have several. An arterial twig enters 

 the corpuscle either from the attached artery or from the out- 

 side. It divides at once into capillaries, which, as a rule, have 

 no regular arrangement. They receive an adventitia of lymph- 

 oid tissue. Most of them soon lose this adventitia, their walls 

 become rich in nuclei, branching processes are given off, and 

 the structural character of the vessel is lost. They finally 



FIG. 173. Prom the spleen of the Tropidonotus natrix : 

 a, follicle, with its capillary plexus ; &, septum, with venous 

 plexus. MfiUer. 



