SMALL INTESTINE. 69 



Submucous coat. Observe its blood-vessels, and perhaps nerve-ganglia (Meissners plexus), 

 and perhaps a solitary gland. 



Muscular Coat. Observe the characters of non-striped muscle cut transversely and longi- 

 tudinally. 



PEYER'S PATCH. 



Transverse Section. (Logwood and dammar.) EXAMINATION (L). Observe the masses 

 of adenoid tissue in the submucous coat. Their conical points project upwards into the gut, 

 and are covered by epithelium, bat no villi exist over them. 



Treble-staining of the Small Intestine. PREPARATION. Take one of the transverse sections 

 of the small intestine, containing a Peyer's patch. Stain it with picrocarmine, wash it lightly 

 in water slightly acidulated with acetic acid. Stain it now with solution of iodine green 

 (p. xlv) until it becomes slightly green, wash it quickly in water, and mount it in dammar, 

 taking care that it does not remain too long in the alcohol. 



EXAMINATION (L). This is an exquisitely beautiful preparation. All the glands, and 

 especially Peyer's patches, are green, all connective tissue is red, and so the submucous layer 

 stands out bright red. The muscularis mucosas and muscular coats are yellow. Observe 

 the interruption of the muscularis mucosae, where the adenoid follicles reach the surface. A 

 thin layer of connective tissue lies superficial to the muscularis mucosae. Such preparations 

 keep a long time. 



In the preparations steeped in osmic acid, after hardening with the chromic acid mixture, 

 the various details are seen with exquisite clearness. 



Blood-vessels of the Small Intestine. Make transverse sections of the small intestine of a 

 cat or dog whose blood-vessels have been filled with a carmine and gelatine mass. Mount in 

 dammar. It is easy to inject the intestine from the superior mesenteric artery. 



EXAMINATION (L). Observe the villi, and note their vascularity. Usually one artery 

 ascends on one side, and splits into capillaries, which are distributed closely under the epithe- 

 lium. The vein descends on the opposite side of the villus. Note the rich plexus of capillaries 

 surrounding Lieberkiihn's glands, and the large arterial trunks in the submucous coat. Study 

 the distribution of the blood-vessels in the muscular coat, and observe that it is not so vascular 

 as the mucous coat. (Indicate the arrangement of the blood-vessels in one half of PI. XIV., 

 Fig. I.) 



Injected Villi seen from above. -Mount in dammar a small piece of the small intestine of a 

 rabbit whose blood-vessels have been injected with a carmine and gelatine mass. Place the 

 section in the slide so that the villous surface is uppermost. 



EXAMINATION (L). Observe the leaflet-like injected villi directed towards the observer, 

 and by focussing through the thickness of the preparation the course and distribution of the 

 larger arterial trunks in the submucous coat can be clearly made out. 



Lymphatics or Lacteals of the Small Intestine. The origin of the lacteal within the central 

 part of a villus as a blind tube has already been noted (p. 68), but the branches of the 

 lymphatics in the walls of the gut can easily be studied, after injection with Berlin-blue, by the 

 puncture method ; an excellent view of their arrangement will be obtained in the prepara- 

 tion of the intestine treated with silver nitrate (p. 37), to show the cement-substance of 

 muscle. This will be referred to again under lymphatics (p. 76). 



