262 



HISTOLOGY 



The glands, villi, and plicae have usually been regarded as permanent structures, 

 serving to increase the secreting and absorbing surfaces of the intestine. In mammals 

 they apparently are not obliterated by the normal distention of the intestine, although 

 the villi may become shorter, the glands shallower, and the plicae may be partially 

 taken up like the folds of the cesophagus. In the guinea-pig, and to some extent in 

 the rabbit and cat, Heitzmann found that the villi change their shape with the intes- 



FIG. 255. EFFECTS OF DISTENTION ON THE SMALL INTESTINE OF THE ADULT GUINEA-PIG. X so. 



(Johnson.) 

 A, Strongly contracted; B, normally distended with food; C, distended with a pressure of rso cm. of water. 



tinal contractions and expansions associated with its physiological activity. Johnson 

 (Amer. Journ. Anat., 1913, vol. 14, pp. 235-250) has shown that in guinea-pigs the 

 villi and glands of the contracted intestine have the form seen in Fig. 255, A; with nor- 

 mal distention due to abundant food, they appear as in B ; v and with extreme artificial 

 distention, the glands and villi are nearly obliterated as in C. The tube expands 

 to this limit, beyond which additional pressure has no effect until it ruptures. On 

 releasing the pressure, glands and villi return to their normal size. Interesting ques- 

 tions are suggested, as to how the muscle fibers become rearranged in the thin layer 

 when the intestine is distended, and what takes place in the blood and lymphatic vessels. 

 These problems are under investigation. 



Finer Structure of the Glands and Villi. At the blind lower end or 

 fundus of the glands, there occur certain cells containing many coarse 

 granules in that part of their protoplasm which is toward the lumen (Fig. 

 256). These cells were first described by Paneth (Arch. f. mikr. Anat., 

 1888, vol. 31, pp. 113-191) and are known as Paneth' s cells. They are 

 found in the glands of the duodenum, jejunum and ileum, but not in those 

 of the large intestine. Although they may be observed with ordinary 

 stains, they are more strikingly demonstrated in iron-haematoxylin prepara- 

 tions. Apparently they produce a special secretion, which enters the 

 lumen of the gland in the form of fine granules when the digestion of fat 



