178 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



We are justified from these experiments in believing that the mechanism 

 of the pancreatic secretion is closely analogous to that controlling the salivary 

 glands. It is usually stated, however, that the pancreas still continues to 

 secrete after all its extrinsic nerves have been severed. The experiments 

 upon which this statement rests are not entirely satisfactory, since, owing to 

 the way in which the nerve-fibres reach the organ in the walls of the blood- 

 vessels, it is difficult to be sure that all the nerve-fibres are actually severed, 

 and moreover it is probable that if the gland continues to secrete after removal 

 of its' extrinsic nerves, the flow is of the nature of a paralytic secretion, which 

 in time would be followed by a wasting of the gland. More experimental 

 work is required upon this point. 



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. 81). 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, which are not found in the pyloric 

 glands, 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 modification 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 in the fact, that they contain distinct vacuoles which 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 



