Transactions . orably affected. (See Fig. I.) The hypophysectomized animal is an excellent test object forthe assay of the growth principle, since positive effects cannot beproduced in the absence of the active principle, and likewise nega-tive results are not confusing, since refractory animals are veryrare. We have suggested as a unit, the smallest amount of extractwhich, administered twice daily for ten days, will cause an averagedaily gain of i gram in rats weighing approximately 100 this basis 100 units have been obtained from i gram of originalanterior lobe tissue. An hypophysec
Transactions . orably affected. (See Fig. I.) The hypophysectomized animal is an excellent test object forthe assay of the growth principle, since positive effects cannot beproduced in the absence of the active principle, and likewise nega-tive results are not confusing, since refractory animals are veryrare. We have suggested as a unit, the smallest amount of extractwhich, administered twice daily for ten days, will cause an averagedaily gain of i gram in rats weighing approximately 100 this basis 100 units have been obtained from i gram of originalanterior lobe tissue. An hypophysectomized animal treated with the growth hor- CHEMISTRY AND PHYSIOLOGY OF PITUITARY HORMONES 57 mone is in in no sense better off than without treatment, sinceincreased body weight is of no significance unless the atrophicthyroid and suprarenal glands are restored as well. This raises amost interesting practical point. Growth hormone in clinical useshould in all probability be used in conjunction with variable a-. <Vj $ §^ ^ 51 R JO ^ f\4 o JO V} V3 < •s. »«. ^» ^ o o o o O s Figure —Showing the effect of the growth hormone upon growth, nitrogenbalance and urinary nitrogen of completely hypophysectomized rats (solid line)and of normal animals (dotted line). At the first arrow the injections were started;at the second, injections were stopped; and at the third, they were started again. 58 J. B. COLLIP mounts of adrenotropic and thyreotropic principles as indicated inthe individual case. 2. The Thyreotropic Principle: The thyreotropic effects of an-terior lobe extracts have long been known. In our experience, it isalmost impossible to prepare a simple extract which does not con-tain the thyreotropic principle. When it was found that the Caa(P04)2 adsorption process as used in preparing growth hormonedid not remove the thyreotropic principle we set about to purifythis substance from the combined filtrates and washings of theCa3(P04)2 used to remove the growth princi
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