DIGESTIVE FLUIDS. 



99 



glands; and in sections vertical to the surface the mucous 

 membrane is shown to consist in greater part of tubular 

 glands, sometimes branched, called the gastric follicles, which 

 may reach -^ inch in length, and are crowded together. 

 They are all lined with columnar epithelium down to the 

 bottom, and the epithelial cells have been seen to undergo 

 a change of appearance 

 in digestion, when the 

 gastric juice is secreted ; 

 but the majority of the 

 follicles likewise contain 

 numbers of large oval 

 and more easily dis- 

 covered cells underneath 

 the columnar epithelium, 

 structures of uncertain 

 function, which, from 

 having been supposed to 

 be the agents in secret- 

 ing pepsin, have been 

 named peptic cells. 



The glands in which 

 these cells occur are 

 called peptic glands, 

 while the others are 

 termed mucous. In some animals, for example the dog, 

 certain regions of the stomach contain none but peptic 

 glands, while the pyloric region has none but mucous glands; 

 and this circumstance has been taken advantage of to deter- 

 mine the character of the secretion furnished by the two 

 kinds of glands. But while one observer (Ebstein) gives a 

 most careful and convincing account of experiments to prove 

 that both kinds secrete pepsin, numerous others come to a 

 different conclusion ; and it may be considered as still un- 

 decided whether the peptic or the columnar cells are the 

 agents by which pepsin is really secreted. 



68. Immediately beyond the pyloric valve, on entering the 

 intestine, the mucous membrane changes its character. Not 

 only is it firmer and thinner, but it is covered over with 

 minute thread-like projections like velvet pile, named mlli, 



Fig. 54. GASTRIC "FOLLICLES. A, Ver- 

 tical section of mucous membrane 

 from the middle of the human stom- 

 ach. B, A more highly magnified 

 view of portion of a gastric follicle 

 of a dog, showing both peptic and 

 columnar cells. From Heidenhain. 



