124 PHYSIOLOGY CHAP. 



swelling and filling with mucus, which bursts through the free 

 end, and is discharged externally. The number of goblet cells 

 varies with the animal and the state of abstinence or digestion. 

 They are specially abundant in the mucous coat of the large 

 intestine, while in the small intestine they are wanting altogether. 

 Brunner's glands are situated in the upper part of the duodenal 

 mucosa; they also extend beyond the pyloric antrum of the 

 stomach, and may be found in the mucous membrane between the 

 crypts of Lieberkiihn. They are small acino- tubular glands, 

 which consist of branching and twisted tubules, ending in pro- 

 longed dilatations or alveoli, which unite into a secretory duct 

 lined with epithelial cells similar to those of the alveoli. These 

 cells resemble those of the pyloric glands of the stomach (Fig. 44). 



FIG. 43. Columnar epithelium from rabbit's intestine. (Schafer.) A, two isolated cells after 

 maceration in very weak chromic acid, showing striated border, and the bright disc which 

 separates them from the cell protoplasm ; n, nucleus with internuclear network ; a, thin pro- 

 jection of cell, which probably fitted between two adjacent cells. B, row of columnar cells 

 from intestinal villus of rabbit ; str, striated border ; w, smaller cells of the nature of lymph 

 corpuscles, between the epithelial cells. 



Little is known about the secretion of Brunner's glands. 

 According to Hirt, they undergo the same modifications during 

 digestion as the pyloric glands ; in the fasting state their 

 cells are comparatively large and clear, in digestion they are 

 small and clouded. Griitzner found that at different distances 

 from the pylorus the glands are in a different functional state. 

 A watery extract of Brunner's glands, freed as far as possible 

 from the duodenal mucosa, contains (according to Krolow) a 

 ferment which digests fibrin, but not boiled egg-albumin, in an 

 acid medium. They must therefore secrete pepsin like the 

 pyloric glands. According to Grtitzner, the enzyme (or zymogen) 

 accumulates during hunger, and discharges during digestion, when 

 the secretory cells become smaller. Mendeldorp also finds a 

 diastatic enzyme in the extract of gland substance. From the 

 little we know as to the nature of the secretion of Brunner's glands 

 their product appears to mix with the acid chyme which passes 

 rhythmically from the stomach to the duodenum, through the 

 pyloric valves, after the first hours of digestion. 



