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THE DUODENUM: A SIPHON TRAP.

By MAYO COLLIER, M.S. Lond., F.R.C.S. Eng.; Senior
Assistant Surgeon, North-West London Hospital; Assistant Demonstrator
of Anatomy, London Hospital Medical College.

We may take it for granted that all gases generated in the jejunum,
ileum, and large intestines pass onward toward the anus, and there
sooner or later escape. Fetid gases--except those generated in the
stomach and duodenum--never pass upward, not even during vomiting due
to hernia, obstruction, and other causes. Physiologists, it would
appear, have never busied themselves to find an explanation for this
apparent breach of the laws of gravity. The intestinal canal is a tube
with various dilatations and constrictions, but at no spot except the
pylorus does the constriction completely obliterate the lumen of the
tube, and here only periodically. It is perfectly evident, then, that,
unless some system of trap exists in the canal, gases are free to
travel from below upward in obedience to the laws of gravity, and
would, as a matter of fact, sooner or later do so. From the straight,
course and vertical position of the oesophagus, a very slight
pressure of gas in the stomach easily overcomes the closure of its
cardiac sphincter and allows of escape. When the stomach has digested
its contents and the pylorus is relaxed, gases generated in the
duodenum can and do ascend into the stomach and so escape. Normally,
no fetid gases are generated in the stomach or duodenum. If we follow
the course of the intestines down, we find that the duodenum presents
a remarkable curve.

Now, there are some points of great interest in connection with this
remarkable, almost circular, curve of the duodenum. In the first
place, this curve is a constant feature in all mammalians. Mr. Treves
says it is one of the most constant features in the anatomy of the
intestines in man, and, speaking of mammalians in general, that the
curve of the duodenum varies in shape, but is never absent, becoming
more complex in some of the higher primates, but seldom less distinct
than in man. In birds the duodenum always forms a long loop embracing
the pancreas.

A second point of great interest is the absolute constancy and
fixation of its terminal portion at the point of junction with the
jejunum, more correctly termed second ascending or fourth portion. Mr.
Treves says that this fourth portion is never less than an inch, and
is practically