THE SPLEEN. 81 



FRESH SPLEEN. 



Cut across a fresh ox spleen. Observe the capsule, trabeculae, and dark grumous-like pulp. 

 The pulp can easily be washed away with a stream of water or salt-solution from a wash-bottle ; 

 the trabecular framework is then easily observed. Observe the Malpighian corpuscles, 

 small white bodies about the size of the head of a pin. Do not mistake transverse sections of 

 the trabeculae for them. Pick out one, and examine it in salt solution (H). It is seen to be 

 made up of lymph-corpuscles, as already described. 



SPLENIC PULP. 

 Tease a small part of fresh splenic pulp in salt solution, and apply a cover-glass. 



EXAMINATION (H). Observe the lymph-corpuscles, perhaps the endothelial cells from a 

 vein, also cells containing particles of fat, others with coloured blood-corpuscles, and some 

 eontaining pigment, besides numerous coloured blood-corpuscles. If the coloured blood- 

 corpuscles are so numerous as to obscure the view of the other elements, tease the pulp in 

 water, which dissolves the blood-corpuscles ; thus the other elements can then be seen more 

 distinctly. 



THE THYMUS. 



The thymus consists of an aggregation of lymph-follicles, or masses of adenoid tissue 

 held together by connective tissue, which contains blood-vessels, lymphatics, and a few nerves 

 The framework consists of a capsule of fibrous tissue, which gives off septa dividing the 

 gland into lobes, these being further subdivided by finer septa into lobules, the lobules being 

 subdivided by fine intra-lobular lamellae of connective tissue into follicles. The gland- 

 substance is made up of these follicles, which are more or less polygonal in outline from mutual 

 pressure. Each follicle consists of a cortical and a medullary part, and-the matrix or frame- 

 work of each consists of 2. fine adenoid reticulum (p. 29), made up of nucleated branched cells, 

 which are easily seen. In this meshwork the lymph-corpuscles lie. In the medulla are found 

 the so-called concentric corpuscles (Hassall). They consist of a central granular part, around 

 which are disposed concentrically layers of flattened nucleated endothelial cells, and on section 

 they present appearances like the ' cell-nests ' that occur in epithelioma. 



PREPARATION (a). Harden part of the thymus of an infant in chromic acid and spirit 

 mixture for two weeks, and then transfer it to alcohol. Stain a section with logwood and 

 mount it in dammar. 



(b~) Harden a similar piece in picric acid for twenty-four hours, and then transfer it to 

 spirit. Sections of this may be beautifully stained with picrocarmine. Mount it in Farrant's 

 solution. The thymus of a kitten or puppy may be used, but these do not show the concentric 

 corpuscles so well. 



EXAMINATION (L). Observe the capsule, the interlobular and intralobular septa of 

 connective tissue, made up of lamellae with flattened corpuscles between them. Note the 

 polygonal or irregularly shaped follicles. Study a follicle. Observe the cortical part stained 

 more deeply with the dye than the medulla. (H). Search for the adenoid reticulum of 



M 



