Summary Balb/c thyroids, held in organ culture for 26 days, survive and function as well as isografts for > 100 days in CBA recipients. Uncultured allografts are totally rejected by 20 days after transplantation. Prolonged allograft survival can also be achieved by the treatment of donor animals with cyclophosphamide prior to harvesting tissues for transplantation. These allografts do not survive as welt as 26 day cultured allografts, but cyclophosphamide pretreatment reduces the culture time required to achieve indefinite survival to 7 days. The provision of an allogeneic (LD) stimulus by thyroid tissue that is I‐region incompatible with the host does not facilitate the rejection of a tolerated cultured allograft. However, activation of the host immune system by an uncultured graft syngeneic to a tolerated cultured allograft leads to the chronic rejection of the cultured transplant. The transfer of a tolerated cultured allograft back to its strain of origin induces an acute inflammatory reaction that causes tissue damage within the transplant but does not lead to the total destruction of the tissue.

Two patients with solitary lesions of pagetoid reticulosis are presented. A third case with disseminated lesions and similar microscopic detail is also reported. Lighg microscopic findings include an abnornal cell infiltrate confined to the epidermis and distributed diffusely in a pagetoid pattern. In ultrathin sections, the abnormal cells are seen to have an abundant cytoplasm with numerous organelles and a convoluted nucleus, often with a prominent nucleolus. The nature of the abnormal cells is discussed. The infiltrate is differentiated from that of mycosis fungoides.

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Summary Leucocytes from inbred AA chickens produced pocks when inoculated onto the chorioallantoic membrane of non‐inbred embryos (direct pock formation), but produced very few or no pocks on the chorioallantoic membrane of syngeneic embryos. Pock formation was observed when AA leucocytes were mixed with non‐inbred embryonic spleen cells before being assayed on the chorioallantoic membrane of recipient embryos that were unresponsive to either cell population alone (indirect pock formation). Indirect pock formation was found to be more radio‐resistant than direct pock formation and doses of Mitomycin‐C that inhibited direct pock formation by AA leucocytes did not inhibit the capacity of these cells to induce indirect pocks. Indirect pock formation was inhibited when non‐inbred embryonic spleen cells were treated with Mitomycin‐C prior to mixing with AA leucocytes. It is suggested that indirect pock formation does not result from the stimulation of adult leucocytes by antigen presented on the surface of allogeneic embryonic cells. Rather, this response is a manifestation of the direct stimulation of embryonic spleen cells by adult allogeneic leucocytes.

Summary.BoUi fi\itl .int\ i^irculiitiriH pliaKOtylk' tvils uiv comcmecl in lhe uptake of foreign matfritti in the chiton Liolophura ^aintardi. Fixed cells are charactcristitally assin-iated with connective tis.sue and are abundant in highly vasculariziii areas sucIi as ths pills and foot. Circulating phagiK-'ytic cells are found anioiiK ths normal hacniocvis population. On the liasis of inorpholoKical and sizK distrihnlion criteria, the haeniiK-ylt-s ftmii a single population of cells. When I'xaniincd t\vcnt> fonr hours after the iiijecHon of foreign material, fixwl cells are iiime hea\ily lahelled than haeniocytcs.Studies cmployinK rhodaiiiine-Iahplled proteiiLS as markers indicate that Liolophura pJiaKocyt't" cells may discriminate Inrtween homoloBoiis protein and bovine .st-runi allmmin. Labelled bovine serum albumin is removi-d from the circulation and taken up by phagocytic cells at a much faster rate than Liolophura haemolymph protein.INTRODUCTION.