260 THE O 



the glands are cut longitudinally, stained with hcEmatoxylin-eosin (technic i, p. 

 20), and mounted in balsam. 



(2) Instead of removing pieces of stomach and pinning them out on cork, as 

 suggested in the preceding technic, the entire stomach may be filled with the 

 fixative, the ends being tied, and then placed in a large cjuantity of the fixing 

 fluid. After fixation, pieces are removed and hardened in graded alcohols. If 

 this method is used, great care must be taken not to overdistend the organ, only 

 very moderate distention being desirable. Further treatment is the same as in 

 the preceding technic (i). 



(3) For comparison of resting with active gastric cells, preparations should be 

 made from the stomach of an animal that has been for from twenty-four to forty- 

 eight hours without food, and from a stomach during active digestion. Fix in 

 Zenker's fluid as in technic i, p. 259. Examine unstained sections and sections 

 stained with hajmatoxylin-eosin. 



(4) Sections through the junction of oesophagus and stomach and through the 

 junction of stomach and duodenum furnish instructive pictures. They should 

 be prepared as in technic i, p. 259. 



(5) For the study of the distribution of the blood-vessels sections of an 

 injected stomach should be made. This is best accomplished by selecting a 

 small animal, such as a rat or guinea-pig, and injecting in toto through the as- 

 cending aorta, or by injecting only the hind part of the animal through the ab- 

 dominal aorta. Technic, p. 25. 



in. THE MIDGUT 



The Small Intestine 



On passing from stomach to small intestine the rugaj of the former 

 disappear, but are replaced by much more definite foldings of the 

 mucosa, the vahula conniventes (Fig. 163). These folds involve the 

 entire thickness of the mucous membrane and part of the submucosa. 

 They are in general parallel to one another, and pass in a circular or 

 obUque manner, partly around the lumen of the gut. The entire 

 surface of the intestine, including the valvulae, is studded with minute 

 projections just visible to the naked eye, and known as villi (Figs. 164 

 and 165). These involve only the epithelium and stroma, although 

 they also contain some muscular elements derived from the muscularis 

 mucosae. The villi differ in shape in the different parts of the small 

 intestine, being leaf-shaped in the duodenum, rounded in the jejunum, 

 club-shaped in the ileum. The valvulae conniventes and the vilh are 

 characteristic of the small intestine. It is important to note that 

 while the pits of the stomach are depressions in the mucous membrane, 

 the intestinal vilU are definite projections above its general surface 

 (Fig. 162). 



The wall of the intestine consists of the same four coats described 



