r directly or indirectly contribute to the
process of digestion are, the mouth, teeth, tongue, and gullet, the
stomach, small intestines, the pancreas, the salivary glands, and the
liver. Next to respiration, digestion is the chief function in the
economy of life, as, without the nutritious fluid digested from the
aliment, there would be nothing to supply the immense and constantly
recurring waste of the system, caused by the activity with which the
arteries at all periods, but especially during infancy and youth, are
building up the frame and developing the body. In infancy (the period of
which our present subject treats), the series of parts engaged in the
process of digestion may be reduced simply to the stomach and liver, or
rather its secretion,--the bile. The stomach is a thick muscular bag,
connected above with the gullet, and, at its lower extremity, with the
commencement of the small intestines. The duty or function of the
stomach is to secrete from the arteries spread over its inner surface, a
sharp acid liquid called the _gastric_ juice; this, with a due mixture
of saliva, softens, dissolves, and gradually digests the food or
contents of the stomach, reducing the whole into a soft pulpy mass,
which then passes into the first part of the small intestines, where it
comes in contact with the bile from the gall-bladder, which immediately
separates the digested food into two parts, one is a white creamy fluid
called chyle, and the absolute concentration of all nourishment, which
is taken up by proper vessels, and, as we have before said, carried
directly to the heart, to be made blood of, and vitalized in the lungs,
and thus provide for the wear and tear of the system. It must be here
observed that the stomach can only digest solids, for fluids, being
incapable of that process, can only be _absorbed_; and without the
result of digestion, animal, at least human life, could not exist. Now,
as Nature has ordained that infantine life shall be supported on liquid
aliment, and as, without a digestion the body would perish, some
provision was necessary to meet this difficulty, and that provision was
found in the nature of the liquid itself, or in other words, THE MILK.
The process of making cheese, or fresh curds and whey, is familiar to
most persons; but as it is necessary to the elucidation of our subject,
we will briefly repeat it. The internal membrane, or the lining coat of
a calf's stomach, having been removed from t