266 DR A. J. WHITING ON THE 



matrix, and wide thin-walled capillaries run among them. This fibrous matrix is 

 apparently derived both from the tunica adventitia of the artery and from the inner 

 layer of the hilar sheath. The follicular cells appear to be of four kinds : (1) The majority 

 are large round cells consisting of a round, deeply stained nucleus surrounded by a rim 

 of protoplasm ; (2) smaller round cells, like free nuclei, staining even more deeply with 

 hsematoxylin ; (3) cells the largest of all, pale and granular, containing a faintly stained 

 vesicular nucleus ; (4) cells similar to the last, but found only in some follicles, 

 containing numerous yellow pigment grains. At the periphery of the follicles is a 

 remarkably distinct zone of muscle, composed of two or three layers of spindle cells. 



In the spleen of the Rabbit the follicles are numerous and well localised. The 

 network of capillaries is unusually conspicuous. Some of the follicles in the adult spleen 

 contain small but distinct germinal centres. The follicular cells are clearly divisible into 

 three concentric areas. The largest cells are, as usual, in the central area, the smaller 

 are in the peripheral zone, and the smallest are in the narrow intermediate zone. The 

 germinal centre is marked off from the intermediate zone by a ring of fibrous tissue con- 

 taining spindle-shaped nuclei. The cells in it are of four kinds : (1) Large cells, consisting 

 of a big vesicular nucleus that stains blue with hsematoxylin, and a small amount of 

 peripheral protoplasm that stains pink with eosine ; each of these is usually enclosed in 

 a cell space : (2) somewhat smaller cells with a round, comparatively small and deeply 

 stained nucleus surrounded by a relatively large amount of protoplasm ; occasionally 

 seven or eight of such cells are found packed together in a cell space : (3) large pigment 

 cells, occasionally seen : (4) small, deeply stained lymphoid cells, possessing a very 

 small amount of protoplasm, if any, around a nucleus which contains a nucleolus. The 

 last kind are specially numerous near the periphery of the germinal centre, and are 

 evidently identical with the cells of the intermediate zone. The capillaries in the 

 central area are larger than those in the other parts of the follicle. Surrounding the 

 follicle is a zone of spindle-shaped cells, many of which are muscular, and external to 

 it is a zone of pulp tissue especially rich in lymphoid cells. 



In the Rat the splenic follicles are remarkable in containing not only branching 

 capillaries, but also, in many cases, branching arterioles. The intrafollicular capillary 

 plexus is very distinct, both on account of the number of capillaries, and on account of 

 the numerous endothelial nuclei in their walls that stain deeply with hsematoxylin. The 

 cells resemble those in the follicles of the rabbit. Around the follicle is a layer of muscle 

 fibre cells, together with a few strands of connective tissue. There is an extrafollicular 

 belt of lymphoid cells, such as are found associated in other spleens with the germinal 

 centre. The intrafollicular reticulum is unusually conspicuous. It is composed of 

 delicate branching filaments, with clear, faintly blue-stained oval cells at the nodal points. 

 It seems to be continuous on the one hand with the wall of the artery, and on the other 

 with that part at least of the limiting fibrous layer that is composed of connective tissue 

 strands. It is distinctly denser and stronger towards the periphery of the follicle. 



In the spleen of the Guinea-pig the greater part of the parenchyma is composed of 



