Observations on the scolex of Echinococcus granulosus, with special reference to the occurrence and cytochemistry of secretory cells in the rostellum

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Abstract
1. The mode of attachment of Echinococcus granulosus to the dog intestine was examined.2. In an attached worm, the scolex was found to penetrate deeply into the crypts of Lieberkühn, with the rostellum fully extended, the hooks penetrating the epithelium lightly and each sucker holding a ‘plug’ of mucous cells in its cavity.3. The expansion of the rostellar tip was aided by a muscular disk, the rostellar pad, which probably assists attachment by forcing the hooks outwards.4. The epithelium in the region of the suckers showed eosinophilic reactions which may indicate a mild host reaction.5. The existence of a small group of spindle-shaped secretory cells which form a rostellar gland, lying immediately anterior to the rostellar pad, is reported. This gland was found to be the source of secretion droplets seen to be released in vitro from the scolex region.6. The secretion droplets were found to be exceptionally labile and not preserved in the rostellar gland cells by routine fixation methods. Prolonged fixation (5–12 months) in formol (7% formaldehyde) gave excellent preservation but globules were fairly well preserved after 3 months fixation. Fixation in Baker's formol-calcium for 2 weeks followed by controlled chromation was also found to retain the secretion reasonably well but not as adequately as the prolonged fixation.7. The secretion was found to be negative to the PAS, bromo-phenol blue (with Hg), and ninhydrin-Schiff reactions. The areas adjacent to the globules gave a protein reaction and the periphery of the globules appeared dark by phase contrast microscopy.8. The secretion was weakly positive to performic acid-Schiff and gave strong reactions with Sudan Black after controlled chromation, both in frozen and wax sections. These results suggest that the secretion may be a liproprotein or a lipid-protein coacervate but it is recognized that confirmation by biochemical methods is desirable.9. The possible immunological implications of these results are discussed.This work was supported by the Australian Wool Research Committee and the U.S. Public Health Service Grant No. E. 4707–02. The technical assistance of Mrs A. L. Warrener and Mr A. B. Howkins is gratefully acknowledged.