1 86 A MANUAL OF VETERINARY PHYSIOLOGY 



granular, and nucleated, and line the lumen of the gland ; they 

 are called the principal, central, or chief cells. Scattered 

 amongst the principal cells, but existing in larger numbers at 

 the neck of the gland than at its base, are found certain large 

 cells (oval, granular, and nucleated), which from their position 

 relative to the lumen of the gland are called parietal, marginal, 

 or border cells. These cells are distinctive of the fundus glands, 

 and they stain readily with aniline blue. 



The pyloric gland (Fig. 67) below its neck has but one variety of 

 cell — viz., the cylindrical — containing a nucleus at its attached 

 edge. The duct is lined, above the neck, by the ordinary epi- 

 thelium of the stomach, and the same remark applies to the 

 fundus glands ; it is from this epithelium that the mucus is 

 secreted. The important distinction between the fundus gland 

 with its principal and parietal cells, and the pyloric gland with 

 only its principal cells, is that the former secretes both the pepsin 

 and acid of the gastric juice (the acid being separated from the 

 blood by the parietal cells) , whilst the pepsin only is formed by 

 the principal cells. The pyloric glands, on the contrary, only 

 secrete pepsin and no acid. 



We have previously mentioned that the cells of the salivary 

 glands undergo certain changes in appearance, the result of 

 rest and activity ; the same remark applies to the gastric follicles, 

 in which the general type of changes during secretory activity 

 is very closely allied to those already described. Langley has 

 found that in the active state the granules decrease in number, 

 the cells becoming clear, and capable of differentiation into a 

 clear outer and a granular inner zone, just as we have seen in 

 the parotid gland ; during rest the entire cell becomes granular. 

 The parietal cells during digestion were found to increase in size, 

 but did not characteristically lose their granules. The central 

 cells secrete both the pepsin and rennin ferments, but in neither 

 case do these exist as such in the cells, but as a mother substance 

 or zymogen of the ferments. The formation by the parietal cells 

 of a free acid from the alkaline blood is a special chemical 

 change, the result of selective powers possessed by the cells. In 

 those animals, such as the dog, yielding hydrochloric acid, the 

 cells very possibly form it by an interaction of the sodium 

 chloride and sodium dihydrogen phosphate of the blood ; but, 

 as a matter of fact, no explanation of how the neutral chlorides 

 are broken up with the formation of hydrochloric acid is at 

 present satisfactory. 



Mucin is secreted by mucous glands found in the deep layers 

 of the villous membrane, especially in the region of the fundus ; 

 the epithelial cells lining the excretory ducts of the gastric glands 

 also take pait in the process. The amount of mucin formed in 



