m which the body can
assimilate. Digestion in the stomach and small intestine is carried on
by means of certain digestive juices, but in the large intestine it is
the bacteria which do the work. Without them we could not live.

Around the colon is a thick network of little blood vessels, all of
which lead straight to the liver, the storehouse of the body. After
the food is fully digested, it is passed through the thin intestinal
wall into these tiny vessels and carried away to liver and muscles for
storage or for immediate use.

This process of absorption is carried on throughout the whole length
of the colon. Not until the very end of the intestine is reached is
all the nutrition abstracted. The bowel-content can properly be called
waste matter only after it has reached the rectum or pouch at the
lower end of the colon. Even then, this waste matter is not poison,
but merely indigestible material which the body cannot handle.

=Food, not Poison.= The colon is not a cesspool but a digestive and
assimilating organ. Its content is not poison but food. Active
elimination is important not so much because delay causes
autointoxication or poisoning as because too large a mass is hard to
manage and irritates the intestinal wall. The problem is not so much
one of toxicology as of simple mechanics. If Nature had put within the
body five feet of tubing which could easily become a cesspool and a
breeder of poison, it is not at all likely that she would have laid
alongside an elaborate system of blood vessels leading not out to the
kidneys but into the storehouse of the liver; and if civilized man's
changed manner of living had so upset Nature's plans as easily to
transform his internal machinery into a chronic source of danger, we
may be sure that he would long ago have gone the way of the unfit and
succumbed to his own poisons.

=Possible Invasions.= It is true that the intestinal tract, like the
rest of the body, is open to attack by harmful bacteria. But in a
great majority of cases, these enemy bacteria are either quickly
destroyed by the beneficent microbes within or are immediately cast
out as unfit. Any germs irritating to the intestinal wall cause the
mucous membrane to produce an unusual flow of mucus which washes away
the offending bacteria in what we call a diarrhea.[52]

[Footnote 52: If the invading army proves obstinate and the diarrhea
continues a day or so, it is wise to assist Nature by a dose of
castor-oil,