LYMPHATIC GLANDS. 77 



becomes slightly white ; snip out the membrane, and after washing expose it to light in the 

 usual way. Mount a small piece in glycerine. 



EXAMINATION (L and H). Observe the membrane perforated here and there by small 

 apertures stomata easily recognised by their having a brownish margin. Their margins are 

 bounded by small, plastic, granular cells, stained brownish with the silver (PL XVII., Fig. 2). 

 The stomata may either be open or closed. In addition, silver outlines are seen, and by focussing 

 through the thickness of the membrane it is seen that epithelium exists on both surfaces, and 

 that the size and shape of the cells differ on the two sides. On the peritoneal surface the cells 

 are elongated, while on the side directed towards the lymph-sac they are more or less polygonal 

 and much broader. Similar stomata exist on the mesogastrium and mesentery of the frog, 

 and in the intercostal pleura, &c., of mammals. They are prepared in the same way. 



if 



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LYMPHATIC GLANDS. 



(A.) COMPOUND LYMPHATIC GLANDS. 



Lymphatic glands are accumulations of adenoid tissue (p. 29) in the course of the lym- 

 phatic vessels, and so they have afferent and efferent vessels. Each gland is surrounded 

 by a connective-tissue capsule, which not unfrequently (ox) contains non-striped muscle, 

 especially in the deeper layers. From its under surface a number of trabeculae carrying blood- 

 vessels pass into the substance of the gland, thus dividing it into a number of compartments 

 or alveoli, which are filled with a network of delicate adenoid tissue, whose meshes are in 

 great part filled with lymph-corpuscles. The gland-substance consists of a cortical and a 

 medullary part. In the cortex the adenoid tissue is arranged in the form of small, round, or 

 oval nodules or follicles, and in the medulla as interlacing cords. The lymph passes through 

 well-marked channels in the gland the lymph-spaces which are spaces lying between the 

 septa or trabeculse and the gland-substance. These spaces are lined by squamous epithelium, 

 and across them is stretched adenoid tissue, which contains few lymph-corpuscles. The 

 structure of adenoid tissue has already been considered (p. 29). 



PREPARATION (a). Place a lymphatic gland from an ox or other animal in Miiller's 

 fluid for a week, and then harden it in spirit and make sections. () Harden a gland in a 

 saturated watery solution of picric acid for twenty-four hours, and preserve in alcohol. Stain 

 a Miiller's fluid section with logwood and mount it in dammar, and stain a picric acid section 

 with picrocarmine and mount it in Farrant's solution. 



Lymphatic Gland. (Logwood and dammar.) EXAMINATION (L). Observe the capsule 

 with its septa subdividing the cortex into a number of compartments of alveoli. As they pass 

 into the centre of the gland the septa break up into trabeculce, which run in all directions, and 

 anastomose with each other, forming a plexus with relatively small meshes, so that it is easy to 

 distinguish the small-meshed medulla from the cortex. Observe the larger alveoli in the 

 cortex. Notice the masses of leucocytes stained deep blue, and between these and the 

 trabeculse narrow spaces, the lymph-sinuses. (Indicate tJie capsule, cortex, and medulla in PL 

 XVII. , Fig. 3). (H). Observe the two layers of the capsule; the superficial layer contains 

 connective tissue and a few elastic fibres, the deep one also non-striped muscular fibres. Study 

 one of the trabeculas, which consist of connective tissue with a few elastic fibres ; and observe 

 the nuclei of the non-striped muscle. The trabeculae are cut in every direction, and branch 



