periment 59. Half fill with dilute hydrochloric acid three large
test tubes, labelled _A_, _B_, _C_. Add to each a few grains of pepsin.
Boil _B_, and make _C_ faintly alkaline with sodic carbonate. The
alkalinity may be noted by adding previously some neutral litmus
solution. Add to each an equal amount--a few threads--of well-washed
fibrin which has been previously steeped for some time in dilute
hydrochloric acid, so that it is swollen and transparent. Keep the tubes
in a water-bath at about 104 degrees Fahrenheit for an hour and examine
them at intervals of twenty minutes.

After five to ten minutes the fibrin in _A_ is dissolved and the fluid
begins to be turbid. In _B_ and _C_ there is no change. Even after long
exposure to 100 degrees Fahrenheit there is no change in _B_ and _C_.

After a variable time, from one to four hours, the contents of the
stomach, which are now called chyme, begin to move on in successive
portions into the next part of the intestinal canal. The ring-like
muscles of the pylorus relax at intervals to allow the muscles of the
stomach to force the partly digested mass into the small intestines.
This action is frequently repeated, until even the indigestible masses
which the gastric juice cannot break down are crowded out of the stomach
into the intestines. From three to four hours after a meal the stomach
is again quite emptied.

A certain amount of this semi-liquid mass, especially the peptones, with
any saccharine fluids, resulting from the partial conversion of starch or
otherwise, is at once absorbed, making its way through the delicate
vessels of the stomach into the blood current, which is flowing through
the gastric veins to the portal vein of the liver.

[Illustration: Fig. 55.--A Small Portion of the Mucous Membrane of the
Small Intestine. (Villi are seen surrounded with the openings of the
tubular glands.) [Magnified 20 diameters.]]

143. The Small Intestine. At the pyloric end of the stomach the
alimentary canal becomes again a slender tube called the small
intestine. This is about twenty feet long and one inch in diameter,
and is divided, for the convenience of description, into three parts.

The first 12 inches is called the duodenum. Into this portion opens
the bile duct from the liver with the duct from the pancreas, these having
been first united and then entering the intestine as a common duct.

The next portion of the intestine i