110 PSYCHOBIOLOGY 



glands, which occur throughout the greater part of the stomach, are simple, 

 or else have few branches. The pyloric glands, which are larger than the 

 fundus glands, occur in the part (about one- fifth) of the stomach nearest 

 the pylorus. The cardiac glands are situated only in a narrow ring near 

 the esophageal orifice : they resemble the fundus glands in size but are com- 

 plex like the pyloric glands. In these glands there are two kinds of cells, 

 chief cells, secreting the digestive enzymes (pepsin and rennet), and 

 parietal cells, secreting hydrochloric acid. The pyloric glands contain 

 only chief cells ; the other gastric glands contain both kinds of cells. These 

 glands are supplied with nerve fibers derived from both the sympathetic 

 and vagal divisions of the visceral nervous system, the immediate supply 

 being from the solar plexus. There are also two local nerve systems in 

 the stomach as well as in the walls of the intestines : the plexus of Auer- 

 bach in the muscular coat, and the plexus of Meissner in the submu- 

 cosa. These plexuses contain numerous ganglion cells and are possibly 

 connected with fibers from the other parts of the autonomic system. 



The gastric glands are excited to activity primarily by the same stimuli 

 (visual, olfactory, tactual, etc.) which excite the salivary glands. The 

 process of gastric secretion has therefore usually been started before the 

 food enters the stomach, although there is a latent period of several minutes 

 before the actual appearance of the juice. Contact with or pressure on 

 the lining of the stomach itself has no effect. By making a gastric fistula 

 and also a fistula in the esophagus, Pavloff proved that the secretion could 

 be produced by the chewing and swallowing of food, or even by the sight 

 of it, although no food entered the stomach. 



Gastric secretion is also excited by the presence of partly digested food 

 in the stomach. This stimulation may be due to the action of substances 

 in the food, or substances (hormones) produced by the glands near the 

 pylorus, acting on the local nervous systems. The greatest experts on the 

 physiology of the internal organs (e. g., Starling), incline, however, to 

 think that the excitation is due to hormones which act directly on the 

 gland cells. 



The intestines are provided with glands of several types. In the walls 

 of both intestines there are many simple tubular glands, Lieberkuhn's 

 glands; and, in the upper part of the duodenum, Brunner's glands 

 (sometimes described as compound-tubular, sometimes as acino- tubular), 

 are plentiful, becoming less numerous below, and being entirely absent at 

 the lower end of the duodenum. Whether the secretions of Brunner's 

 glands and Lieberkuhn's glands in the small intestines differ is not de- 

 cided. In conjunction, these glands produce intestinal juice (succus 

 entericus) . The Lieberkuhn's glands in the large intestine produce a dif- 



