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Page 20
Fourth, The bile; which no physiologist as yet thoroughly understands. We
know its action, but hardly _why_ it acts. It is a necessity, however; for
if by disease the supply be cut off, an animal emaciates and soon dies.
Fifth, The intestinal juice; which has some properties like saliva, and is
the last product of the digestive forces.
A meal, then, in its passage downward is first diluted and increased in
bulk by a watery fluid which prepares all the starchy portion for
absorption. Then comes a still more profuse fluid, dissolving all the
meaty part. Then the fat is attended to by the stream of pancreatic juice,
and at the same time the bile pours upon it, doing its own work in its own
mysterious way; and last of all, lest any process should have been
imperfect, the long canal sends out a juice having some of the properties
of all.
Thus each day's requirements call for
PINTS.
Of saliva 3-3/4
gastric juice 12
bile 3-3/4
pancreatic juice 1-1/2
intestinal juice 1/2
-------
21-1/2
Do not fancy this is all wasted or lost. Very far from it: for the whole
process seems to be a second circulation, as it were; and, while the blood
is moving in its wonderful passage through veins and arteries, another
circulation as wonderful, an endless current going its unceasing round so
long as life lasts, is also taking place. But without food the first would
become impossible; and the quality of food, and its proper digestion, mean
good or bad blood as the case may be. We must follow our mouthful of food,
and see how this action takes place.
When the different juices have all done their work, the _chyme_, which is
food as it passes from the stomach into the duodenum or passage to the
lower stomach or bowels, becomes a milky substance called _chyle_, which
moves slowly, pushed by numberless muscles along the bowel, which squeeze
much of it into little glands at the back of the bowels. These are called
the mesenteric glands; and, as each one receives its portion of chyle, a
wonderful thing happens. About half of it is changed into small round
bodies called corpuscles, and they float with the rest of the milky fluid
through delicate pipes which take it to a sort of bag just in front of the
spine. To this bag is fastened another pipe or tube--the thoracic
duct--which follows the line of the spine; and up this tube the small
bodies travel till they come to the neck and a spot where two veins meet.
A door in one opens, and the transformation is complete. The small bodies
are raw food no more, but blood, traveling fast to where it may be
purified, and begin its endless round in the best condition. For, as you
know, venous blood is still impure and dirty blood. Before it can be
really alive it must pass through the veins to the right side of the
heart, flow through into the upper chamber, then through another door or
valve into the lower, where it is pumped out into the lungs. If these
lungs are, as they should be, full of pure air, each corpuscle is so
charged with oxygen, that the last speck of impurity is burned up, and it
goes dancing and bounding on its way. That is what health means: perfect
food made into perfect blood, and giving that sense of strength and
exhilaration that we none of us know half as much about as we should. We
get it sometimes on mountain-tops in clear autumn days when the air is
like wine; but God meant it to be our daily portion, and this very
despised knowledge of cookery is to bring it about. If a lung is
imperfect, supplied only with foul air as among the very poor, or diseased
as in consumption, food does not nourish, and you now know why. We have
found that the purest air and the purest water contain the largest
proportion of oxygen; and it is this that vitalizes both food and, through
food, the blood.
To nourish this body, then, demands many elements; and to study these has
been the joint work of chemists and physiologists, till at last every
constituent of the body is known and classified. Many as these
constituents are, they are all resolved into the simple elements, oxygen,
hydrogen, nitrogen, and carbon, while a little sulphur, a little
phosphorus, lime, chlorine, sodium, &c., are added.
FLESH and BLOOD are composed of water, fat, fibrine, albumen, gelatine,
and the compounds of lime, phosphorus, soda, potash, magnesia, iron, &c.
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