From what we have just said it is evident that the proper emptying of the stomach and, therefore, the proper carrying on of the whole process of digestion, depends upon the formation and outpouring of ample supplies of acid-containing gastric juice. A failure of gastric secretion is bound to be followed by a failure of the stomach to empty itself. Instead of going on to the small intestine where digestion is completed and the digestion products passed on to the blood stream to be used by the body, the food mass lies inert in the stomach. After a few hours, if not immediately, the acute symptoms of indigestion are certain to develop. We are describing not a theoretical possibility but an actual happening in the life of thousands of people, sometimes almost daily. Indigestion is one of the great causes of misery and of impaired efficiency throughout the civilized world. It is said that Napoleon lost the Battle of Waterloo on account of an acute indigestion which befell him on the morning of the crucial day. There are several causes of indigestion. Among them should be mentioned food poisoning; that is, the inadvertent taking of some material which instead of being a food proves to be actively poisonous. A second type about which we shall have something to say presently is the result of poisoning by substances which are products of the putrefaction of the intestinal contents. A third type, and the one in which we are particularly interested at this moment, is the one which results from the failure of gastric juice to be properly secreted. A fourth occasional cause of indigestion, which should be mentioned in passing, is that which results from eyestrain, and is avoided by properly fitted glasses. There is comparatively little food poisoning; most persons who are susceptible to poisoning from particular kinds of foods find it out promptly and learn to avoid the article which poisons them. A good deal of indigestion is the direct result of intestinal sluggishness; this usually comes on gradually enough to give warning of its approach. Sharp attacks for which there seems to be no justification are nearly always the result of the failure of gastric secretion. Because of the practical importance of this topic a very large amount of study has been devoted to it, and its story makes one of the very fascinating chapters of physiology.