XXV.] SMALL INTESTINE. 273 



(iii.) Cut sections by freezing and place some in i per cent, osmic 

 acid (24 hours). This sharpens the outlines of many of the structures. 



(iv.) It is convenient in teaching to give a complete transverse 

 section of the small intestine of a small animal, e.g., mouse or 

 kitten. In herbivora the wall of the gut is very thin. Stain in 

 bulk and cut in paraffin. Flemming's fluid is an excellent " fixing " 

 reagent both for the small and large intestine. Stain the sections 

 in safranin. 



1. T.S. Small Intestine (L). Observe the serous, muscular, 

 submucous, and mucous coats (fig. 260). 



(a.) In the mucous coat, the surface beset with small conical 

 projections villi which, if they are contracted, exhibit wrinkles 

 on their surface. At the bases of the villi a single layer of simple 

 test-tube-like glands glands of Lieberkunn or intestinal glands, 

 embedded in an adenoid tissue matrix. Outside this the muscu- 

 laris mucosae. 



(b.) The submucous coat, composed of fibrous tissue with nerves 

 and blood-vessels. 



(c.) The muscular coat, composed of two layers, an outer longi- 

 tudinal and an inner circular layer. In the cat, the latter is much 

 thicker than the former. 



('/.) The serous coat. 



(e.) (H) Study a villus. Observe the single layer of granular 

 nucleated columnar epithelium covering it, each cell with its free 

 end covered by a clear disc, with vertical strise (fig. 260). The 

 succession of these free clear borders looks like a clear hem round 

 the circumference of the villus. Occasionally leucocytes may be 

 seen between the cells. 



(/'.) The goblet cells, chalice, or calictform cells scattered among 

 the former (fig. 260). They may be seen from the side, or their 

 open rounded mouths may be directed toward the observer. When 

 seen from the side, they are ovoid, with a larger and clearer upper 

 part containing mucigen, and a smaller, lower, granular, nucleated 

 part (Lesson V.). Sometimes a plug of mucus may be seen protruding 

 from the mouth of a cell. It is stained blue with logwood and brown 

 with Bismarck brown. If the mucous glands be active and the fresh 

 tissue be fixed in osmic acid, then the plug of mucus is black. 



(g.) In the centre of the villus a vertical space, the radicle of a 

 lacteal, with a thin nucleated wall. The substance of the villus 

 consists of adenoid tissue beset with leucocytes. Close under the 

 epithelium, perhaps, sections of capillaries, and a little farther in 

 one or more strands of non-striped muscle, which can be traced to 

 the apex of the villus, and downwards to the muscularis mucosse 

 (fig. 260, MM). 



(h.) The glands of Lieberkuhn lined by short columnar nucleated 

 25 S 



