356 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



juice along the sides of the cannula. The subject must, therefore, be left 

 where we started : the stomach during life does not digest itself, but its 

 immunity cannot be satisfactorily explained. 



3. The Secretion of Gastric Juice. — The walls of the stomach are 

 constituted by four coats, composed externally of the peritoneum or 

 serous layer; se cond, the muscular layer, composed of longitudinal, cir- 

 cular, and oblique unstriped muscular fibres ; third, the submucous layer 

 of connective tissue, in which are found numerous blood-vessels, lymphat- 

 ics, and glands; and, fourth, the inter- 

 nal mucous coat, in which are found 

 the glands of the stomach. The mu- 

 cous membrane is covered throughout 

 its entire extent by a single layer of 

 narrow, cylindrical, epithelial cells 

 similar to the ordinary mucus-secreting 

 goblet cells. The tubular glands of 

 the stomach are of two distinct kinds, 

 traversing the mucous membrane ver- 

 tically and differing greatly as they 

 are located in the cardiac or pyloric 

 portions of the stomach. The glands 

 found in the iiarcliac portion of the 

 stomach or fundus are called the peptic ' 

 glands, and consist of several short 

 tubules opening into a broad duct 

 which is lined by epithelial cells similar 

 to those on the free mucous membrane 

 of the stomach. The lower portions of 

 the tubes, those portions which alone 

 form the gastric secretion, are lined by 

 a layer of small granular, columnar, 

 nucleated cells (Fig. 148). These 

 cells border the lumen of the gland 

 and are termed the chief or central 

 cells. At various places between 

 these cells and the membrana propria are large, oval or angular granu- 

 lated, nucleated cells, which are termed parietal cells. These cells are 

 most numerous in the necks of the glands and less so in the lower ends of 

 the tubules (Pig. 149). They are stained deeply by osmic acid and 

 aniline blue, and bulge out the membrana propria opposite to where they 

 are placed, and are thus readily recognized. 



The pyloric glands (Fig. 150) are generally branched at their lower 

 ends, several tubes opening into a single duct, which is Ions; and wide. 



Fig. 148.— Glands op the Fundus of 

 the Stomach. (Hcirttnhain.) 



