It was but a step, we can now realize, from the employment of isolated vegetable principles to that of preparations of certain glandular organs of the animal economy, but the doctrine of "internal secretions" had to intervene, and its evolution took time; not till toward the close of the century did the venerable Brown-Séquard lead up to it. We have not yet come to "eye of newt and toe of frog," but what we have incorporated into modern therapeutics in the way of animal products lends at least some theoretical justification to the ancient use of the dried organs of various animals. It is but a few years since the "ductless glands"--such organs, as, for example, the thyreoid gland (an organ situated in the front of the neck, a small affair in its normal state, but prominent and even pendulous when by its permanent enlargement it comes to constitute a goître)--were looked upon as puzzles, as structures destitute of any known function. Some observers even affirmed that they had no function, though the constancy of goître in cretins ought to have shown the fallacy of this allegation in the case of the thyreoid. We do not now need to be told that the thyreoid gland plays a very important part in the economy, for we know that its surgical removal gives rise to a special disease known as myxoedema, which, in addition to its physical manifestations, is characterized by impairment of the mental powers. Consequently, this ductless gland--a gland, that is to say, which has no obvious canal by which it throws off any product of its activity--must elaborate some material that is necessary to the health of the organism and is imparted to the blood. That material, whatever it may be, is termed an "internal secretion." Some of the internal secretions have turned out to be of singular value medicinally. It is apparently not the ductless glands alone that furnish internal secretions; the glands that are provided with ducts and yield a definite and observable product secrete also a substance (perhaps more than one) which they give up to the blood.