Abstract Not Available.

Over the last decade the tempo of research on the parathyroid gland and its relationship to metabolism has increased rapidly. As new advances in our knowledge of calcium and phosphorus metabolism are made, old ideas and theories must be re-evaluated and some modified, others discarded. New concepts of parathyroid function are being brought forth from the mass of literature which is accumulating. A reversal of thought is taking place regarding both the primary site of action of the parathyroid hormone and the mechanism of control of its secretion. For years it was stated that the primary action of the hormone was to regulate the kidney threshold for phosphorus excretion. In keeping with this idea, it was also felt that the phosphate level of the serum was the direct controlling agent of parathyroid hormone secretion. Enough evidence has now accumulated to show that the primary action of the parathyroid hormone is probably on bone rather than on the kidney. In addition, it is now widely accepted that the serum calcium level controls the secretion of the hormone. To date there has been a general lack of evidence for the exclusive control of hormone secretion by calcium. This is due, in large measure, to the lack of an adequate index of endogenous parathyroid activity. It has been heretofore difficult, if not impossible, to adequately assess the degree of parathyroid secretion under a number of physiological conditions. It is hoped that the work presented herein will prove helpful in providing additional evidence in support of the latter proposition.

Both electron microscopy and light microscope histochemistry have been used to describe the cytology of the hypodermis of the parasitic nematode, Capillaria hepatica. The hypodermis of the mid portion of the body of this species forms a complete cellular layer around the worm and may be divided into the following regions: the multicellular lateral and ventral chords; the interchordal hypodermis, apparently formed by flat processes of the cells of the multicellular chords; and the dorsal chord, probably formed by the internal reflection of the hypodermal cell processes which form the interchordal hypodermis. The cytology of the hypodermal gland cells which occur within the multicellular chords is described in detail. The elaboration of the infolded cell membrane of the gland cell forms a region of the cell termed the lamellar apparatus. This region is associated with a pore through the cuticle, but is separated from this pore by an area termed the pore chamber which contains a gel-like material. The outer margin of this material is marked by a boundary layer while diffuse, granular cap material is associated with the outer surface of this layer. No morphological evidence has been found to suggest that the cell is glandular in function, but the structure of the lamellar apparatus would be consistent with the suggestion that the cell may function in either osmotic or ionic regulation. Experiments in which the osmotic value of the external environment of the worms was altered offer no evidence either for or against such a function. The uptake of neutral red and colloidal gold by the hypodermis is similarly inconclusive, but shows that such materials are concentrated into vacuoles within the non-glandular hypodermal cells. Glycogen, the chief storage product of the body wall, occurs in the basal two-thirds of the non-glandular cells. The possible significance of the concentration of the most of the organelles of the non-glandular cells in the apical cytoplasm is discussed. The structure of the six-layered cuticle, and of the somatic musculature is described, and the relationship of the hypodermis to these tissues is discussed. No evidence has been found for the existence of pore canals extending from the hypodermis into the cuticle, nor of supportive fibrils extending from the muscle cell into the hypodermis.

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