SECRETION. 237 



ably after these substances have reached the duodenum. Moreover, Pawlow 

 has given proof that the secretion of the pancreas varies in both quantity and 

 quality with the nature of the food. Indeed, there seem to be indications of 

 a specific relationship between the food and the composition of the secretion, 

 albuminous food giving a secretion with a greater digestive action on pro- 

 teids; oily foods, a secretion with a larger amount of fat-splitting enzymes, 

 and so on. If this relationship is shown to exist, it forms an adaptation whose 

 mechanism is very obscure.' 



Glands of the Stomach. 



Histological Characteristics. — The glands of the gastric mucous mem- 

 brane belong practically to the type of simple tubular glands ; for, although 

 two or more of the simple tubes may possess a common opening or mouth, 

 there is no system of ducts such as prevails in the compound glands, and the 

 divergence from the simplest form of tubular gland is very slight. Each of 

 these glands possesses a relatively wide mouth, lined with the columnar epi- 

 thelium found on the free surface of the gastric membrane, and a longer, nar- 

 rower secreting part, which penetrates the thickness of the mucosa and is lined 

 by cuboidal cells. The glands in the pyloric end of the stomach differ in gen- 

 eral appearance from those in the fundic end, and are especially characterized 

 by the fact that they possess only one kind of secretory cell, while the fundic 

 glands contain two apparently distinct types of cells (Fig. 64). The lumen in the 

 latter glands is lined by a continuous layer of short cylindrical cells to which 

 Heidenhain gave the name of chief-cells. These cells are apparently concerned 

 in the formation of pepsin, the proteolytic enzyme contained in the gastric secre- 

 tion. In addition there are present a number of cells of an oval or triangular 

 shape which are placed close to the basement membrane and do not extend quite 

 to the main lumen of the gland. These cells are not found in the pyloric glands ; 

 they are known by various names, such as border-cells, parietal cells, oxyntic 

 cells, etc. The last-mentioned name has been given to them because of their 

 supposed connection with the formation of the acid of the gastric secretion. The 

 nature and function of these border-cells have been the subject of much discus- 

 sion. From the histological side they have been interpreted as representing 

 either immature forms of the chief-cell, or else the active modificatioD of this 

 cell. Recent work, however, seems to have demonstrated that they form a 

 specific type of cell, and probably therefore have a specific function. An 

 interesting histological fact in connection with the parietal cells is that, in the 

 human stomach at least, they frequently contain several nuclei, five or six, 

 and some of these seem to be derived from ingested leucocytes. They are 

 interesting also is the fact that they contain distinct vacuoles that seem to 

 appear some time after digestion has begun, reach a maximum size, and then 

 gradually grow smaller and finally disappear. Like the similar phenomenon 



1 For other interesting facts bearing upon the mechanism of pancreatic secretion, see Walter : 

 Archives des Sciences biologiques, 1899, t. vii. p. 1. 



