The Body at Work: A Treatise on the Principles of PhysiologyHill, Alex
Science
The Body at Work: A Treatise on the Principles of Physiology
Hill, Alex
Physiology
We may describe as a typical meal one consisting of bread, vegetables,
cane-sugar, meat, milk, fat, and cheese. In the mouth the various foods
are crushed and mixed with the alkaline secretions of the salivary
glands. A certain amount of the cooked starch contained in the bread
is changed into maltose. In the stomach the digestion of starch is
continued for a time, but a large part even of the cooked starch awaits
the action of pancreatic juice. A certain amount of cane-sugar is
converted into dextrose and levulose, which are rapidly absorbed into
the blood; but this action is due to hydrochloric acid, and probably
affects a comparatively small part of the cane-sugar swallowed. Fat is
quite unaltered in the stomach. All proteins are attacked by pepsin,
but some yield to digestion more readily than others. Gluten of bread,
like all vegetable proteins, is comparatively resistant; but since
it is presented to the action of pepsin in small quantities and in a
spongy form—very suitable for digestion—it is probable that most of
it is peptonized in the stomach. Chemists experimenting with gastric
juice taken from the stomach, and reproducing the conditions as to
temperature, removal of products of action, etc., as closely as it is
possible to reproduce them in the laboratory, find that the various
foods take different times to digest. The proteins of meat are more
quickly peptonized when raw than after coagulation by heat. The same
is true of white of egg. Amongst different varieties of cooked flesh,
beef is more quickly peptonized than fish. The casein of milk is more
quickly peptonized than any other protein; and it also is no exception
to the rule that digestibility is diminished by cooking. Similar data
may be obtained for all foods. They are no doubt useful indications of
the course of action which we may expect to occur within the stomach,
but we can never be sure that my lord will obey the ruling of the
chemist. Practice with a captive golf-ball is a useful preparation
for the game; but there are conditions on the links which cannot be
reproduced on the lawn. In an artificial stomach the clean fibre of
raw fish digests more slowly than raw beef. Even when the beef is
roasted and the fish fried or boiled in the ordinary way, the beef
disappears through the dialyser (the bag of membrane suspended in a
vessel of warm water in which experimental digestion is carried out)
more quickly than the fish. Nevertheless, the living stomach is better
disposed towards a mixed meal containing a certain weight of fish than
towards a meal in which, the other constituents remaining the same,
beef takes the place of fish. Important conclusions may, no doubt,
be drawn from observations of the time occupied in the peptonization
of pure food—_i.e._, fibrin, white of egg, clean meat, etc.—under
conditions simulating those which are present in the stomach; but
they must be accepted with many reservations. In the stomach it is
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