lacteals and mostly by the sense serves as a
capillaries, way of the that energy carrier of
but to the liver. foods are. all the
greater other
extent by constituents
the of the
capilaries. blood.
Common salt Undergoes Taken up by By way of Not stored. In solution.
no change. the portal
capillaries vein,
without liver, and
undergoing hepatic
apparent veins into
change. inferior
vena cava.
Oxygen Taken up by Already in Is not United with
the the general stored. the
capillaries circulation. hemoglobin
at the and to a
lungs. small extent
in solution
in the
plasma.

*Tissue Enzymes.*--The important part played by enzymes in the digestion of
the food has suggested other uses for them in the body. It has been
recently shown that many of the chemical changes in the tissues are in all
probability due to the presence of enzymes. An illustration of what a
tissue enzyme may do is seen in the changes which fat undergoes. In order
for the body to use up its reserve fat, it must be transferred from the
connective tissue cells, where it is stored, to the cells of the active
tissues where it is to be used. This requires that it be reduced to the
form of a solution and that it reenter the blood. In other words, it must
be _redigested_. For bringing about these changes a substance identical in
function with the steapsin of the pancreatic juice has been shown to exist
in several of t