It is to the science of chemistry that we owe our knowledge of the
composition of the various foodstuffs from which dietaries are selected,
as well as of the several parts of the human body which relies for its
sustenance on those dietaries. But the adjustment of dietaries to the
work they have to do is a more complex problem than those we have
hitherto considered. We learn from the science of physiology that the
human body is a laboratory in which certain juices are secreted for the
digestion of foods, and that in this laboratory foods must be reduced
to the consistency necessary for their passage through animal membranes;
for it is by passage through membranes that the nutritive parts of food
find their way into the general circulation of the blood which carries
them to all parts of the system. Very few foodstuffs are available for
use in their natural state, and the majority of them are prepared for
consumption in the first place by more or less elaborate processes
included in the art of cookery. When thus prepared they should be in a
fit state to undergo in the body the physical changes comprised in
mastication, and the chemical changes associated with the process of
digestion.
It might be surmised by the thoughtful parent that as the child's body
lacks some of the external features of the adult body, such as hair and
teeth, so there might, and probably would, be corresponding lapses in
the internal economy, and that therefore the food prepared for the adult
would be, even in the smallest quantity, unsuited to the child.
Physiologists tell us that this is so, and in particular that the
secretions which in adult life are called saliva and pancreatic juice
and which have the function of preparing starch for digestion, are at
this time scanty in amount and deficient in chemical action. But these
secretions are essential for the digestion of starchy foods, and
chemists tell us that starch abounds in the vegetable kingdom from which
most of the food of children is derived. It is therefore a matter of
some importance that every person in charge of an infant should have
that amount of knowledge of chemical reactions which is requisite to
enable them to detect whether a food does or does not contain starch. A
child fed entirely on starchy foods suffers from malnutrition of so
serious a character that death may, and often does, ensue. Even if other
suitable food, such as modified milk, be given, the internal economy of
the child will be seriously disturbed.
The names by which patent foods are advertised are very often misleading
to unscientific persons, and invalids have suffered much from the
mistaken idea that jellies and meat extracts are foods. Meat extracts
have their use, but any invalid fed on extract of beef only would die
sooner than one left with no food at all. The reason for this can be
learned from the knowledge of the constituents of beef extracts and the
part they play in the human organism.