~Composition of Gastric Juice.~--In a former chapter the processes of gastric digestion were explained. The gastric juice, composed of from 0.2 to 0.3% free hydrochloric acid and several important enzymes and lipases, which act upon the proteins and emulsified fats, must be sufficient in quantity to assure good digestion, and when anything arises to interfere with the secretion of this fluid a deviation from the normal is bound to occur. ~Disturbed Motility and Tone.~--Again, it has been proved that good gastric digestion, like good intestinal digestion, depends more or less upon the way in which the food mass is mixed with the digestive juices and moved along the alimentary canal. Anything which interferes with the secretion of the juices or delays the food over its normal length of time in the stomach surely exerts unfavorable influences on the general metabolism of the food, for while, as we have already found, gastric digestion is not essential to the final utilization of the food in health, in disease it undoubtedly exerts a marked influence upon the general nutrition of the individual. HYPOCHLORHYDRIA The lack of hydrochloric acid in the gastric juice lowers the resistance to bacterial action, for this constituent exerts a decided germicidal influence in gastric digestion, preventing fermentation with the production of organic acids and probably alcohol. In conditions due to hypochlorhydria (lack of hydrochloric acid) foods which leave the stomach quickly must be given with enough of the other necessary constituents in their simplest and most easily digested form to balance the diet and prevent the occurrence of the other disorders as troublesome as the original disorder.