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In this monograph of 92 pages, Collin continues his study on the pituitary. He deals with the anatomy and physiology more particularly. Its innervation is complex: the diencephalon receives sensory afferent fibers from the olfactory, optic, auditory and from general and local receptors. The diencephalon emits to the pituitary gland the hypothalamic-pituitary tract and to the mesencephalo-ponto-bulbo-medullary centers (BM) the diencephalon emits caudal efferent pathways (tangential periventricular system). From the BM centers arise vegetative efferent pathways. The pituitary receives also sympathetic fibers from the superior cervical ganglion into which afferent fibers have entered.
Resulting from the innervation, the physiology of the pituitary is no less complex. There are 1) olfactory-pituito-gonadal reflexes. Certain olfactory stimuli are capable of releasing pituitary gonado-tropic hormones. Olfactory impressions may have a vegetative repercussion by means of the hypophysis as intermediary. This justifies the general view that the vegetative functions and the primitive instincts—which have self—and race preservation as goal—are conditioned by olfactory stimuli: search for food, adaptation to environment, flight from enemy, sexual attractions, etc.
There are 2) optico-pituito-pigmentary reflxes by which the stimulating rays of light retina, cause color changes in the skin of animals, a protective mechanism that makes for adaptation to the color and light or dark of the surroundings. The chromatocytes or chromatophores in the skin are the final part of the reflex arc. Besides adrenalin, the sympathetic, the neuro-hormones can also take part in pigment regulation. Hypophysectomy in amphibians results in albinization on account of a diminution of the black pigment and its concentration in the center of the chromatophores. On the other hand, implanation of hypophyses or injection of its extrac produces melanization.
There are 3) optico-pituito-sexual reflexes. In these