XX.] THE SPLEEN. 245 



small lob-sided aggregations of lymphoid tissue around branches of 

 the splenic artery. They are relatively more numerous than in the 

 human spleen. The track of the blood in the pulp is mapped out 

 by the yellow blood-corpuscles. 



(c.) (H) The capsule and trabeculae, composed of fibrous tissue, 

 with elastic fibres and smooth muscle. The Malpighian corpuscles, 

 consisting of leucocytes in an adenoid reticulum. The centre is 

 lighter in tint than the circumference, which is more condensed. 

 The lighter centre is due to the larger cells present there. They 

 are undergoing proliferation. The cells formed in the splenic 

 corpuscles pass into the spaces of the pulp and leave the organ by 

 the venous blood stream. 



(d.) In the pulp irregular rows of coloured blood-corpuscles 

 yellow and between these leucocytes and other cells. 



The exact structure of the pulp can only be properly studied in 

 a section which is very thin, and especially at the edges of the 

 section, or best of all in a section of a dog's (or cat's) spleen, whose 

 blood-vessels have been washed out, and cleared of all blood- 

 corpuscles by a warm stream of normal saline solution. The 

 vessels are then injected with a 5 per cent, solution of ammonium 

 bichromate, and the organ hardened in a large quantity of the same 

 fluid, and subsequently in alcohol. 



(e.) In a section prepared in this way, or at the edges of a very 

 thin section, the fine reticulum of branching cells may be seen 

 (fig. 233) with the cells of the splenic pulp washed out of it. 



10. Human Spleen. Harden this in the same way as 8. Note 

 that, as a rule, the Malpighian corpuscles are less numerous. In 

 other respects the general structure is the same. 



11. Injected Spleen. It is very difficult to inject the finer splenic 

 blood-vessels. They should be washed out first with normal saline, 

 and preferably a watery solution of Berlin blue, or Berlin blue with 

 gelatine, should be used as the injection. Note that an artery and 

 capillaries exist in the Malpighian corpuscles, but the splenic pulp 

 seems to be infiltrated with a blue mass. The capillaries open into 

 this system of labyrinthine blood-passages. These intermediate 

 blood-passages are merely the spaces amongst the cells of pulp and 

 arc not lined by epithelium. The terminations of the capillaries 

 in some situations are surrounded by thick sheaths or collars of 

 tissue, perhaps derived from the cells of the pulp (Banntcartk). 1 



12. The varieties of Leucocytes in lymph glands are best studied 

 by fixing the gland in Hg C1 and staining sections with Ehrlich- 

 Biondi lltiid (Hoyer).' 2 There are at least four varieties, not including 

 phagocytes. 



1 Arcliivf. mile. Anat., xxxviii. p. 345. 2 Ibid., xxxiv. 



