[Sidenote: Peristaltic movement in alimentary canal]
Another point to be considered in digestion, and which may well be
classed under the mechanics of digestion, is the muscular action or
peristalsis of the alimentary tract. The best example is the swallowing
action observed in the throat of a horse, or of a cow, when drinking. At
each swallow, what appears to be a lump goes down the throat. This is a
wave-like relaxation of the muscular walls of the esophagus, followed
closely by a muscular contraction. This is the action that takes place
in the intestinal tract, and that which Nature employs to move the
contents along toward the final point of excretion.
[Sidenote: X-ray examination of peristalsis]
A very fascinating and scientific demonstration may be performed in the
following manner: A cat may be given food mixed with some such substance
as bismuth subnitrate, which is opaque to X-rays. Upon placing the
animal under an X-ray during digestion, this peculiar peristaltic motion
can be observed, one "swallow" passing rapidly after another down the
alimentary tract.
This method of investigation has also shown that peristaltic action
stops immediately in the case of fright, or anger, but is shown to
proceed with regularity during sleep, contrary to the antiquated idea
that digestion ceases when sleep begins.
[Sidenote: Milk for relieving constipation]
Peristaltic action in the lower parts of the alimentary canal is
stimulated by taking food into the stomach. This explains the laxative
action of such foods as fruits, or, sometimes, milk, taken at frequent
intervals. When all other methods fail, constipation can oftentimes
be relieved by taking a glass of milk every thirty minutes until four
glasses have been consumed.
[Sidenote: Moisture and peristaltic action]
The longer food remains in the intestines, the more completely is the
water absorbed from the residue. The object to be obtained in relieving
constipation is to increase the moisture and the peristaltic action.
Whatever will accomplish these things will relieve and perhaps cure
intestinal congestion.
The subject of intestinal congestion and purgative medicines will be
discussed at length in Lessons IX and XI, Vol. II, p. 375 and p. 436,
respectively.