. Elements of biology, with special reference to their rôle in the lives of animals. Biology; Zoology. Fig. 168.—Fully charged, partially discharued, and almost completely discharged secretory cells in the pancreas of a toad. (After Child: Senescence and Rejuvenescence, published by the University of Chicago Press.) such simple substances as hydrochloric acid to exceedingly complex organic molecules. It is not )'et understood how a nerve impulse sets in motion the physical and chemical processes of glandular action. Secretory activity represents the expenditure of energy, for active glands abs
. Elements of biology, with special reference to their rôle in the lives of animals. Biology; Zoology. Fig. 168.—Fully charged, partially discharued, and almost completely discharged secretory cells in the pancreas of a toad. (After Child: Senescence and Rejuvenescence, published by the University of Chicago Press.) such simple substances as hydrochloric acid to exceedingly complex organic molecules. It is not )'et understood how a nerve impulse sets in motion the physical and chemical processes of glandular action. Secretory activity represents the expenditure of energy, for active glands absorb more oxygen than do resting glands. It is also known that electrical factors are involved, for an active gland is electro-negative to adjacent tissues. The secretions are apparently formed in connection with certain plastids in the cytoplasm; fur- thermore, resting glands often contain stored-up materials that are seen to disappear when the gland becomes active (Fig. 168). Some glands secrete constantly; others are active only during stimulation. The activity of the gland may be a response to a nerve impulse or to some chemical activator. For example, the salivary glands become. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Buchanan, James William, 1888-. New York, London, Harper & brothers
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