as the fact that they
possessed no visible pathways for the removal of their secretion. So
now they were set apart as the _ductless_ glands, the glands without
ducts, as contrasted with the glands normally equipped with ducts.
Since, too, they were observed to have an exceedingly rich supply of
blood, the blood presented itself as the only conceivable mode of
egress for the secretions packed within the cells. So they were also
called the blood or vascular glands.

The names which became most popular were those which represented a
contrast of the glands with the ducts, conveying their secretion to
the exterior, as the glands of EXTERNAL SECRETION and the glands
without the ducts, the secretions of which were kept within the body,
absorbed by the blood and lymph to be used by the other cells, as
the glands of INTERNAL SECRETION. How different these two classes
of glands are may be realized by imagining the existence of great
factories manufacturing food products, which would diffuse through
their walls into the atmosphere, to be absorbed by our bodies.

There are certain terms for the glands of internal secretion which
are used interchangeably. They are spoken of often as the _endocrine_
glands and as the _hormone_ producing glands. Endocrine is most
convenient for it stands for both the gland and its secretion. Hormone
is employed a good deal in the literature of the subject. But it
applies specifically to the internal secretion, and not to the gland.

THE EXPERIMENTAL PIONEER

All this clarification of the concept of the glands of internal
secretion occurred in the first quarter of the nineteenth century.
However, no inkling of their real importance to the body, of which
quantitatively they form so insignificant a part, was apparently
revealed to anyone. Not even the most daring speculation or brilliant
guess work in physiology engaged them as material. Thus Henle, the
great anatomist, calmly affirmed that these glands "have no influence
on animal life: they may be extirpated or they degenerate without
sensation or motion suffering in the least." Johann Mueller, the most
celebrated physiologist of his day and contemporary of Henle, wrote
in 1844 and coolly stated, "The ductless glands are alike in one
particular--they either produce a different change in the blood which
circulates through them or the lymph which they elaborate plays a
special role in the formation of blood or of chyle." In other words,
they were di