-Human bile, the secretion most actively concerned in the
digestion and absorption of the fats, contains water, bile salts, bile
acids, bile pigments, cholesterin, lecithin, and a peculiar protein
derived from the mucous membranes of the bile ducts and gall bladder.

~Stimulation of Intestinal Secretions.~--The flow of the intestinal
juices is stimulated by a substance or _hormone_ known as
"~secretin~." This hormone is the result of the action of hydrochloric
acid upon some substance in the intestinal wall. Starling claims that
the formation of hormones and their circulation through the blood to
the reactive tissues is sufficient to account for the activity of the
pancreas; he doubts if the nervous system plays any part in the
activity of that organ.

~Secretion of Water in the Stomach.~--The secretion of water by the
cells of the stomach is such, according to Taylor, as to produce
chyme of quite constant consistency, the solid particles being held in
suspension in the fluid medium.

~Factors Influencing Gastric Digestion.~--The factors influencing
digestion in the stomach constitute all those mechanical, electrical,
chemical, and psychical factors which stimulate or retard the action
of the gastric juices. The movements in the stomach are involuntary,
but their activities may be stimulated by the flow of gastric juice.
Sleep retards digestion in the stomach by retarding the movements in
the organ itself.

~Stimuli to Gastric Flow.~--The division and liquefaction of the food
in the mouth hastens gastric digestion by making the food better
fitted for the action of the enzymes in the gastric juice. The type as
well as the character of the food acts as a stimulus to the gastric
secretion.

~Water~ is probably the best of all the agents for stimulating the
secretion of gastric juice, while ~dextrin~ (toast, zwieback) and the
~extractives of meat~ likewise exert similar powers.

~Retarding the Gastric Flow.~--The nervous system, on the other hand,
at times checks or entirely inhibits a flow of these juices. Worry,
excitement, anger, fatigue, chill; each plays its part in promoting
poor digestion in the gastric organ. As chemical factors, water and
salts are the two necessary substances for gastric digestion, since
the enzymes in the juices cannot act except in their presence.

~Alkaline carbonates~ and ~fatty foods~ both check the flow of gastric
juice, and retard digestion. The psychic factors which result in a
st