rments; (4) secretion of mucus; (5) protection of the body against
organismal infection, and against toxic products; (6) absorption of food
elements and reconstitution of them into complex substances fitted for
metabolic application; and (7) excretion of the waste products of
protoplasmic action. These functions may be altered by disease, singly
or in conjunction; it is rare, however, to find but one affected, while
an apparently identical disturbance of function may often arise from
totally different organic lesions. Another point of importance is seen
in the close interdependence which exists between the secretions of acid
and those of alkaline reaction. The difference in reaction seems to act
_mutatis mutandis_ as a stimulant in each instance.

_General Diseases._

Vascular lesions.

In all sections of the alimentary canal actively engaged in the
digestion of food, a well-marked local engorgement of the blood-vessels
supplying the walls occurs. The hyperaemia abates soon after completion
of the special duties of the individual sections. This normal condition
may be abnormally exaggerated by overstimulation from irritant poisons
introduced into the canal; from too rich, too copious or indigestible
articles of diet; or from too prolonged an experience of some unvaried
kind of food-stuff, especially if large quantities of it are necessary
for metabolic needs; entering into the first stage of inflammation,
acute hyperaemia. More important, because productive of less tractable
lesions, is passive congestion of the digestive organs. Whenever the
flow of blood into the right side of the heart is hindered, whether it
arise from disease of the heart itself, or of the lungs, or proceed from
obstruction in some part of the portal system, the damming-back of the
venous circulation speedily produces a more or less pronounced stasis of
the blood in the walls of the alimentary canal and in the associated
abdominal glands. The lack of a sufficiently vigorous flow of blood is
followed by deficient secretion of digestive agents from the glandular
elements involved, by decreased motility of the muscular coats of the
stomach and bowel, and lessened adaptability throughout for dealing with
even slight irregular demands on their powers. The mucous membrane of
the stomach and bowel, less able to withstand the effects of irritation,
even of a minor character, readily passes into a condition of chronic
catarrh, while it frequently is t