XX.] 



LYMPHATIC GLANDS. 



239 



raise it, and cut out a square window about f inch in diameter, 

 including the whole of the posterior body-wall. This exposes the 

 dorsal surface of a thin membrane, the septum of the great lymph- 

 sac. It is attached to the kidneys on each side. Pin the 

 membrane, by means of hedgehog-spines, to a thin ring of cork 

 with a hole in it, "Wash the membrane with distilled water and 

 place it for ten minutes in . 5 per cent, silver nitrate solution. Wash 

 it still on its ring of cork in distilled water, and expose it to 

 light. After it has become brown, cut it into pieces, and mount 

 them in Farrant's solution, one with the peritoneal surface upper- 

 most, the other with its dorsal surface uppermost. 



A. (H) Peritoneal Surface. Observe the slightly sinuous 

 "silver lines," indicating the existence of 



a single layer of endothelium. Here and 

 there small stomata or openings, which 

 lead from the peritoneal cavity to the great 

 lymph-sac (fig. 226). The stomata may 

 be closed or open, and are recognised by 

 their brownish appearance. They are sur- 

 rounded by a few finely-granular brown- 

 stained cells germinating epithelium. 

 The pointed angles of several of the larger 

 endothelial cells radiate from these aper- 

 tures. 



Focus through the thickness of the 

 membrane, and note its fibrous character. 

 ( hi the deeper surface another layer of 

 endothelial cells comes into view. They 

 are more sinuous and narrower than those 

 on the peritoneal surface. 



B. The Dorsal or Cisternal Surface. Observe the more sinuous, 

 polygonal, and broader endothelial cells covering this surface of 

 the membrane ; and the other openings of the stomata. 



The serous cavities communicate by means of stomata with the 

 lijmphatic system. Stomata occur on the pleura, under-surface of 

 the diaphragm, and mesentery =, 



FIG. 226. Endothelium and 

 Stomata of the Peritoneal 

 Surface of the Septum Cis- 

 ternse Lymphaticse Magnte 



of the Frog, x 200. 



THE TONSILS. 



6. Tonsils. Use those of rabbit or cat, as the human tonsil 

 does not give such good results. Fix them in Kleinenberg's 

 fluid (12 hours), and then harden in gradually-increasing strengths 

 of alcohol. Or use mercuric chloride or Flemming's fluid (3-6 

 hours). Make sections by the paraffin method, and stain them 



