258 ELEMENTARY PHYSIOLOGY LRsa. 



far described in the body of the villus is filled up with 

 adenoid (lymphoid) tissue, whose meshes are more or less 

 crowded with leucocytes. 



The epithelium covering a villus is made up of cells of 

 two kinds. Of these the large majority are tall, columnar, 

 and granular, with an oval nucleus towards their inner 

 end. The outer end of each cell (on the surface of the 

 villus) shows a narrow, strongly striated border (Fig. 82). 

 Lying between these are cells which, from their shape, 

 are often called " goblet " cells, but which in structure are 

 practically the same as the nuicous cells of the submaxillary 

 gland already described (p. 238). These cells secrete the 

 mucus which covers the inside of the intestine. The 

 columnar cells are concerned in the absorption of digested 

 food. 



13, The Structure of the Pancreas and its Changes 

 dliring Secretion. — The pancreas is a raccMUose gland, 

 but tlie alveoli in which the ducts end are somewhat 

 elongated as compared with their more rounded shape in the 

 salivary glands. The cells in each alveolus are not unlike 

 those of the parotid gland (p. 239). When the gland has 

 been at rest for some time the cells are large, their outlines 

 indistinct, and the central part of each is thickly loaded 

 with very obvious granules (Fig. 83, A). After the gland 

 has been secreting for some time, the cells are smaller, 

 their outline distinct, and the granules have largely dis- 

 appeared. Those granules which remain are now placed 

 at the inner ends of the cells next to the lumen of the 

 alveolus (Fig. 83, B). These differences in the appearance 

 of the cells in the two conditions of rest and activity 

 show quite clearly that while at rest these cells build 

 up material which is lodged in their substance as ob- 

 vious granules and discharge this material as part of the 

 secretion as soon as they become active. Thus the changes 

 taking place in the cells of the pancreas during se- 

 cretion are essentially the same as those previously 

 described in the case of the salivary glands, and have 



