brain and spinal cord. What offices do these sets of organs perform
in the great labor-specializing aggregation of cells which we call a
living organism?

As regards the ductless glands, the first clew to their function was
given when the great Frenchman Claude Bernard (the man of whom
his admirers loved to say, "He is not a physiologist merely; he is
physiology itself") discovered what is spoken of as the glycogenic
function of the liver. The liver itself, indeed, is not a ductless
organ, but the quantity of its biliary output seems utterly
disproportionate to its enormous size, particularly when it is
considered that in the case of the human species the liver contains
normally about one-fifth of all the blood in the entire body. Bernard
discovered that the blood undergoes a change of composition in passing
through the liver. The liver cells (the peculiar forms of which had been
described by Purkinje, Henle, and Dutrochet about 1838) have the power
to convert certain of the substances that come to them into a starchlike
compound called glycogen, and to store this substance away till it
is needed by the organism. This capacity of the liver cells is quite
independent of the bile-making power of the same cells; hence the
discovery of this glycogenic function showed that an organ may have
more than one pronounced and important specific function. But its chief
importance was in giving a clew to those intermediate processes between
digestion and final assimilation that are now known to be of such vital
significance in the economy of the organism.

In the forty odd years that have elapsed since this pioneer observation
of Bernard, numerous facts have come to light showing the extreme
importance of such intermediate alterations of food-supplies in the
blood as that performed by the liver. It has been shown that the
pancreas, the spleen, the thyroid gland, the suprarenal capsules
are absolutely essential, each in its own way, to the health of the
organism, through metabolic changes which they alone seem capable of
performing; and it is suspected that various other tissues, including
even the muscles themselves, have somewhat similar metabolic capacities
in addition to their recognized functions. But so extremely intricate is
the chemistry of the substances involved that in no single case has the
exact nature of the metabolisms wrought by these organs been fully made
out. Each is in its way a chemical laboratory indispensable