intestines
and the kidneys.

A brief description of these processes seems desirable here.

~Digestion.~--Mechanical digestion begins in the mouth, where through
the action of the teeth, the tongue and the muscles of the jaw, the
food material is ground up and liquefied to a certain extent and made
ready for the chemical action which takes place, to a limited degree
only, as a result of the salivary enzyme in the mouth. The eating of
food causes a flow of saliva from the three pairs of large salivary
glands, and from the numerous secretory cells situated in the
membranes of the mouth. As a rule the food stays for too short a time
in this organ for any appreciable amount of chemical action to take
place, but the liquefaction of the food mass with the salivary juices
which contain the ferment (ptyalin), prepares for its passage into the
gastric organ, and allows the digestion of the starch (the only
foodstuff affected by salivary digestant), to continue in that part of
the stomach until its action is checked by the hydrochloric acid in
the gastric juice.

~Arrangement of Food in the Stomach.~--To simplify the study of the
gastric organs it may be well to think of the stomach as being divided
into three regions, _i.e._, "the fundus, the middle region, and the
pyloric end,"[52] each of which differs slightly from the other. After
being swallowed, the food enters the region situated at the cardiac
end, known as the fundus.

~Motor Processes in the Stomach.~--There are no peristaltic waves in
the fundus of the stomach, and the movement of the food mass is
accomplished through the stretching and contraction of the muscular
walls of the organ which tends to churn and further mix it with the
salivary juices as it is gently pushed out into the middle region. In
this region the peristaltic waves begin and travel toward the pylorus
and increase in force as digestion progresses, ceasing only with the
emptying of the organ. When the first stratum of food reaches the
middle of the stomach it is caught by these oscillating peristaltic
waves and forced forward through the pyloric region and against the
pylorus, from whence it is returned back through rings of
constriction. This forward and backward movement continues as long as
there is food in the stomach, thus thoroughly mixing the mass with the
gastric juice and allowing the enzymes existing in the juices to have
an opportunity for action (chemical digestion).

~Passage of Foo