of it.  All we can say about it is that it is probably due to a paralysis of all the glands of internal secretion, a removal of their influence upon the cells.  Contrariwise to the feeding of thyroid, removal of the thyroid of tadpoles will prevent their development into frogs.  If iodine is then fed to them, say mixed with flour, normal metamorphosis will occur.  If Body is the tool chest which we carry about with us, as Samuel Butler said, then to the thyroid belongs the name of tool-maker.

Another function of thyroid that must be taken into consideration is what has been spoken of as its antitoxic function—­in plainer English, its power to prevent poisoning, or to increase resistance against poisons, including the bacteria and other living agents which cause the infectious diseases.  Each molecule of food, ingested for assimilation into our substance, accumulates a history of wanderings and pilgrimages, attachments and transformations beside which the gross trampings of a Marco Polo become the rambling steps of a seven-league booted giant.  In the course of its peregrinations, it becomes a potential poison, potential because it is never allowed to grow in concentration to the danger point.  The thyroid plays its role of protector like all the internal secretory machines.  In an animal deprived of a thyroid the feeding of meat shortens life—­a single sample of how it works to guard against intoxication from within.  The feeding of thyroid will also raise the ability of the cells to stand poisons introduced from without—­intoxications of all sorts.  Alcohol and morphine will affect in much smaller doses the subthyroid person than the normal or the hyperthyroid.  As regards the infections, which directly or indirectly kill most of us, the injection of thyroid will increase the content in the blood of the protective antibodies which preserve us, temporarily at any rate, against malignant invaders.  The opsonins, for example, those substances which butter the bacteria so that the appetite of the white cells for them is properly roused, are mobilized by thyroid feeding or injection.  Other substances in the blood which destroy and dissolve bacteria are also increased.  The thyroid probably performs these functions by sending its secretion to the cells directly responsible for the immunity reactions, and stimulating them to activity.

A sketch of the thyroid like the foregoing shows it as the wondrous controller of vitality and growth, and indefatigable protector against intoxicants and injuries.  When it is sufficiently active, life is worth while; when it is defective, life is a difficult threatening blackness.  That would make it out as the gland of glands.  It is tremendously important, without a doubt, in normal everyday life.  But no more so than the other members of the cast.  The position of star it may claim, but in vain.  The other glands of internal secretion to be sketched will each, when the marvels of its business in the cell-corporation are considered, present itself as candidate for the honors of the president.  Justice should give fair credit to all the organs which fabricate the reagents of individuality, and the regulators of personality.