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n the first half of the nineteenth century the accepted view of the phenomena of secretion was that enunciated by Johannes Müller, viz., that the process consists of two phases—secretion proper, or the casting out of substances upon a surface inside the body, as in the case of the gastric juice; and "excretion" or the voiding of such secreted substances into the external world, as in the case of bile or urea. This distinction was somewhat artificial, since bile, urea and other excreted substances are also secretions in the first instance. In 1801 the French physiologist Legallois, as Gley has noted, surmised, from the identity in composition of all varieties of arterial blood and the diversity of venous blood in different parts of the body, that this diversity is acquired, in each case, from the loss of some substance to the organ from which the vein proceeds. Thus Borden's idea: $$ A $$ (arterial blood) $$ =S $$ (secretion) $$ + V $$ (venous blood), and Legallois's idea: $$ V $$ (venous blood) $$ = A $$ (arterial blood) $$ -S $$ (secretion) are identical. When $$ A $$ and $$ S $$ are chemically known, $$ A $$ being constant, $$ V $$ will be known; or, when $$ A $$ and $$ V $$ are known, $$ S $$ will be known. $$ V $$ is always a variable. This remarkable intuition of Legallois, like the hypothesis of Borden, remained on a theoretical basis and was not put to experimental proof. In 1849, A. A. Berthold, a Göttingen professor, is said to have transplanted the testes of a fowl to another part of its body, with complete retention of its sexual characters, a phenomenon which he inferred to be due to "the productive relation of the testes, i. e., to its effect upon the blood and thence through the corresponding effect of such blood upon the entire organism." This aperçu, again, does not differ materially from that made by Bordeu in the eighteenth century. In the meantime the ductless glands were coming to be known among the German physiologists as "blood-vessel glands" (Blutgefässdrüsen) or "blood glands" (Blutdrüsen) and were regarded by the histologists Henle and Kölliker as preparers of different chemical substances which are utilized by the organism through the blood. Beyond this general theory, which is identical with Borden's, no special function could be assigned to the different ductless glands. Even Henle asserted that these glands have no influence whatever upon animal life, that they can be extirpated or undergo pathological degeneration without affecting either the sensory or motor functions of the body. The path-breaking importance of Addison's great monograph on the effect of disease of the suprarenal capsules may be thrown into relief by citing Hyrtl's witticism about the suprarenal—that the