ul
experiments have proved that it is a _constant_ secretion; but its flow
is mere abundant during digestion. During the passage through the
intestines it disappears. It is not eliminated, and Pettenkoffer's test
has failed to detect its existence in the portal vein. These facts lead
physiologists to the conclusion, that it undergoes some transformation
in the intestines and is re-absorbed.

After digestion has been going on in the stomach for some time, the
semi-digested food, in the form of chyme, begins to pass through the
_pyloric orifice_ of the stomach into the duodenum, or upper portion of
the small intestine. Here it encounters the intestinal juice, pancreatic
juice, and the bile, the secretion of all of which is stimulated by the
presence of food in the alimentary tract. These fluids, mingling with
the chyme, give it an alkaline reaction, and convert it into chyle. The
transformation of starch into sugar, which is almost, if not entirely,
suspended while the food remains in the stomach, owing to the acidity of
the chyme, is resumed in the duodenum, the acid of the chyme, being
neutralized by the alkaline secretions there encountered.

Late researches have demonstrated that the pancreatic juice exerts a
powerful effect on albuminous matters, not unlike that of the gastric
juice.

Thus, it seems that while in the mouth only starchy, and while in the
stomach only albuminous substances are digested, in the small intestine
all kinds of food materials, starchy, albuminoid, fatty and mineral, are
either completely dissolved, or minutely subdivided, and so prepared
that they may be readily absorbed through the animal membranes into the
vessels.

MILK. The milk is a white, opaque fluid, secreted in the lacteal glands
of the female, in the mammalia. These glands consist of numerous
follicles, grouped around an excretory duct, which unites with similar
ducts coming from other lobules. By successive unions, they form large
branches, termed the _lactiferous ducts_, which open by ten to fourteen
minute orifices on the extremity of the nipple. The most important
constituent of milk is _casein_; it also contains oily and saccharine
substances. This secretion, more than any other, as influenced by
nervous conditions. A mother's bosom will fill with milk at the thought
of her infant child. Milk is sometimes poisoned by a fit of ill-temper,
and the infant made sick and occasionally thrown into convulsions, which
in some inst