It will be remembered that the flow of saliva is modified by the appetite as well as by the length of time through which mastication is continued. The flow of gastric juice is modified by the appetite and by the character of the food. The work of the stomach is very greatly facilitated and, therefore, its work more perfect and more readily and quickly accomplished if the food has been not only well chosen and well prepared, but also properly masticated. The presence of the alkaline saliva also stimulates the flow of gastric juice, so in a measure, all other things being equal, the greater the amount of saliva brought in with the food, the more rapid and easy is the work of the gastric glands.

Finally, the flow of the intestinal secretions is greatly modified, if not actually governed, by the action of the segments of the alimentary canal, through which the food has already passed. While appetite exerts an influence upon the action of the pancreas, it is especially influenced by the introduction into the duodenum of acid from the stomach. The greater the activity of the gastric gland, the greater the activity of the pancreas and the intestinal glands.

Recent researches show that this is accomplished through the agency of the secretin as follows: The greater the amount of acid entering the duodenum the greater the amount of secretin produced by the wall of the intestine. The secretin is absorbed and carried by the blood to the pancreas. The more secretin brought to the pancreas, the more pancreatic juice secreted. Thus, ultimately, the more acid in the stomach, the more alkali in the intestine.

From this it must be evident that if a wrong start is made in the process of digestion, the whole process will be hampered and delayed. Fortunately for all of us, the beginning of this process is wholly under the control of the will. Every person has the power of making the right start and of controlling the beginning. If one knows these principles here laid down and utilizes them continually, he may confidently expect that his digestive processes will be normal.

The influence of the appetite is so profound and far reaching that one may say, no appetite no eating. If one has no appetite, his digestive processes will be greatly retarded, if not actually associated with pain and discomfort, and the amount of actual nourishment gained from a meal thus eaten is not great enough to justify the danger of the undertaking. I would, therefore, emphasize again by repetition the paramount importance of observing this general rule: If one has no appetite he should abstain from food. Sometimes through exhaustion one feels faint and feels that he needs nourishment, but he has no appetite. Instead of forcing food under such conditions, it would be incomparably more wise to drink one or two glasses of cold water, repair to one's room to lie down and absolutely relax for twenty or thirty minutes. After this period of relaxation the probabilities are strong that the person will experience a good appetite for his meal.

Two great laws of hygiene which may be formulated in summing up the subject of digestion are: First, eat only when prompted by appetite. Second, chew the food and mix it with saliva until it has been reduced to an impalpably fine state of division and is of a thin, creamy consistency. When food is thus chewed one is hardly conscious of the swallowing process, and still less conscious of the subsequent digestive processes which all follow in rapid, easy succession.