Post-embryonic genesis of bursal follicles in the duck

The structural and histological characteristics of the limiting layer between the cortex and medulla of the bursa of Fabricius in the duck are described in relation to different functional moments of the organ. On E.M. study the limiting layer, in duck having 30 days of age, is constituted of reticular-epithelial cells palisades in shape with many cytoplasmics extension. Lymphatic migration occur in interstitial spaces.     

Long-acting contraceptive agents: Norethisterone esters of arylcarboxylic acids

The synthesis of esters of norethisterone (17α-ethynyl-17β-hydroxy-estr-4-en-3-one) with acids containing a benzene ring is described, two methods of esterification being compared in terms of yield and convenience. The activities of these esters as long-acting contraceptive agents have been evaluated.     

A STUDY OF GLUCO-CORTICOSTEROID-INDUCED PYKNOSIS IN THE THYMUS AND LYMPH NODE OF THE ADRENALECTOMIZED RAT

Pyknotic nuclei, observed in the thymus of steroid-treated rats, are dense, homogeneous, intensely basophilic and Feulgen positive. Under the electron microscope, the image is that of a complete segregation of the chromatin from the nuclear sap producing a margin or crescent of condensed chromatin. Approximately 30% of all small thymocytes appeared to undergo this type of degeneration within 3–4 hr after administration of the synthetic corticosteroid, dexamethasone. At this time, pyknotic thymocytes were observed in clusters, probably as a result of the activity of dense reticular cells and macrophages. Topographical and experimental data suggest the existence of a select population of steroid-sensitive thymic cells. Furthermore, on the basis of thymidine-³H incorporation studies, it appears that the steroid-sensitive population of thymocytes does not correspond to "aged" cells. In addition, many plasma cells became pyknotic after the same steroid treatment, indicating an unexpected similarity between their nuclei and those of lymphocytes. Finally, steroid failed to induce pyknosis of thymocytes in a variety of in vitro experiments, suggesting that the in vivo effect of steroid is of an indirect nature. The results are discussed in terms of (a) the nature of the nuclear changes characterizing pyknosis, (b) the hypothetical mechanism whereby steroids trigger such changes, and (c) the population of cells susceptible to steroid-induced pyknosis.     

Abnormalities in synaptonemal complexes in pollen mother cells of a lily hybrid

Two abnormalities, one in lateral elements of synaptonemal complexes the other involving whole complexes, have been studied with the electron microscope in pollen mother cells of the lily hybrid, Lilium aureliensis × L. henryi, which with the light microscope showed almost complete bivalent formation at metaphase. Brief water treatment of pollen mother cells prior to fixation, revealed that the aberrant configurations in lateral elements arose by breakage and subsequent folding of severed fragments up to about 0.8 m long. The abnormality ocurred at recognisable heterologous regions, apparently immediately after pairing. The folded fragments were eliminated from the chromosomes at some time during pachytene. Pseudo pairing was observed after synapsis between either more than one pair of homologues or one pair bent back on themselves, so as to produce polycomplexes. Seemingly, central elements could develop between lateral elements on their outer face under these conditions.