DIGESTIVE SECRETIONS AND THEIR CONTROL 441 



acid and glycerin; the trypsin of pancreatic juice*, in cooperation 

 with erepsin of the succus entericus reduces all proteins, includ- 

 ing proteoses and peptones, to amino acids; the inverting enzyms, 

 maltase, invertase, and lactase, change all the double sugars, and 

 therefore all the carbohydrates of the meal, to single sugars. The 

 intestinal contents (chyle) are churned and kept in onward 

 progress by movements of segmentation and peristalsis performed 

 by the muscular walls of the gut. 



The Maintenance of Good Digestion. In the preceding para- 

 graph the various activities essential to the proper performance 

 of the digestive function have been outlined. If they are reviewed 

 carefully it will be seen that most of them, after the food reaches 

 the stomach, are affected, directly or indirectly, by the conditions 

 upon which depend the proper production of the psychical secre- 

 tion of gastric juice. If, through anxiety or anger at meal-time, 

 this secretion is inhibited, the whole sequence of the digestive 

 process is upset. Without a psychic secretion little or no chemical 

 secretion of gastric juice will appear; there is therefore not the 

 necessary hydrochloric acid to stimulate the pyloric sphincter to 

 relax, nor to react with prosecretin to form pancreatic secretin, 

 should any food by any means get through into the intestine. 

 Moreover, the same conditions which inhibit the psychical secre- 

 tion inhibit also, as stated previously, the motions of the stomach 

 and intestines. That indigestion usually follows the eating of 

 meals under unfavorable emotional conditions is well known to all; 

 the reason for it we have just seen. Of as great importance, 

 though not so generally recognized, is that the psychical secretion, 

 and hence good digestion, depends upon an active emotional state 

 of enjoyment of the meal. Preoccupation, allowing the mind to 

 dwell upon business or household cares, may interfere with the di- 

 gestive processes only less seriously than worry or angry discussion. 



The value of soups in aiding digestion is twofold. By exciting 

 the appetite they help to arouse the psychical secretion; their con- 

 tent of meat juice is itself in some measure an excitant of the 

 hormone to chemical gastric secretion, thus they are usually effect- 

 ive in starting the chain of events which make up the digestion of 

 a meal. The practice of using them at the beginning rather than 

 elsewhere in the meal, although long antedating our knowledge of 

 their real value is thus seen to be physiologically sound. 



