feeding grain flushes at least a part of the undigested grain from the
stomach through the small intestine and into the caecum. New grains, such
as new oats, are hurried along the small intestine and reach the large
intestine practically undigested. The two latter conditions are common
causes of _flatulent_ or _wind colic_. Sudden change in the ration,
especially to a green feed, may result in intestinal irritation and
flatulence.

[Illustration: FIG. 15.--Photograph of model of digestive tract of
ruminant: oesophagus; rumen; reticulum; omasum; abomasum; small intestine;
and large intestine.]

Horses that are greedy feeders and have sharp, uneven, smooth or diseased
teeth are unable to masticate the feed properly. This results in
unthriftiness caused by imperfect digestion and assimilation of the feed.
Such animals usually suffer from a catarrhal or chronic inflammation of the
intestine, and may have periodic attacks of acute indigestion or colic.

_Obstruction colic_ is very often caused by the feeding of too much
roughage in the form of straw, shredded fodder, or hay. Debility often
contributes to this form of indigestion, and the double colon may become
badly impacted with alimentary matter.

Worms may irritate the intestinal mucous membrane and interfere with
digestion, obstruct the intestine and cause debility and circulatory
disturbances. The large round worm may form a tangled mass and completely
fill a portion of the double colon.

[Illustration: FIG. 16.--A yearling colt that died of aneurism colic.]