y secreted human milk, lactose
occurs in quantities ranging from 6 to 7%, and in the milk of cows and
goats from 4 to 5%. Lactose is much less soluble than sucrose, and
decidedly less sweet; hence, owing to this latter property, as well as
to its lack of susceptibility to fermentation, lactose is frequently
used to bring up the sugar content of infant formulas to the desired
percentage, and the diets used in the abnormal conditions when
additional energy material is needed. During the process of digestion,
lactose is hydrolized by the lactase in the intestinal juice, yielding
one molecule of glucose and one of galactose. Like maltose, little if
any of this sugar is absorbed in its original form, since experiments
made with injections of lactose into the blood result in the rapid and
almost complete elimination by way of the kidneys. No such results are
obtained when even large amounts of lactose are taken by way of the
mouth.

~Polysaccharides.~--This group of carbohydrates is complex in
character, built up of many sugar molecules, and upon digestion must
be broken down into simple sugars before they can be utilized by the
body.

~Starch~ is the form in which the plant stores her supply of
carbohydrates. It is found in this form in roots and (mature) tubers,
three-fourths of the bulk of which is made up of this material. From
one-half to three-quarters of the solids of grains is made up of
starch also. Pure starch is a fine white powder, odorless and almost
tasteless. It is insoluble in cold water and alcohol, but changes from
an insoluble substance to a more soluble one upon the application of
heat. Upon hydrolysis starch gives first a mixture of dextrin and
maltose, then glucose alone as an end-product. This hydrolysis may be
the result of enzymic action, as occurs upon bringing starch in
contact with the ptyalin in the saliva, or with the amylopsin in the
pancreatic juice; or it may be the result of boiling starch with acid,
as is seen in the manufacture of commercial glucose.

~Dextrin~, as has already been stated, is an intermediate product of
the hydrolysis of starch by acid or enzymes.

~Glycogen~ is the form in which the carbohydrates are stored in the
body, just as starch is the form in which they are stored in plants.
It is found in all parts of the body, but is especially abundant in
the liver. Here it is stored in the cell substance rather than in the
nucleus. The storage of glycogen in the human body d