Early deglaciation of the labrador shelf

Two marine sediment cores from a basin on the southeastern Labrador Shelf penetrate a mud sequence extending back to 21,000 carbon-14 years before the present (B.P.). The benthic foraminifera are dominated by subartic nearshore species indicative of ice-free summer waters. The pollen record indicates the presence of a sedge-shrub tundra in eastern Labrador as early as 21,000 years B.P. Both sources of evidence suggest less extensive continental ice than has previously been reported for this subarctic region.     

Evaluation of reconstitution of immunodeficient mice by partially purified thymic extracts.

Partially purified thymus products were used to evaluate the maturation of T lymphocytes in immunodeficient mice. Three different bovine thymic extracts, designated thymic extracts A, B, and C, were successful in increasing the longevity of conventionally raised nude mice. Daily injection of bovine thymic extracts A, B, and C and mouse thymus extracts failed to mature a population of T lymphocytes and restore the capacity to reject heart allografts. Preincubation of normal syngeneic bone marrow with thymic extract B in vitro before injection into nude mice also failed to reconstitute the host's ability to reject heart grafts. The number of antibody plaque-forming cells of sheep red blood cells in lethally irradiated, bone marrow-reconstituted mice could be increased by preincubating the bone marrow cells with bovine thymic extract fraction B before injection followed by daily injections. A similar but less marked increase in plaque-forming cells was obtained by the daily injection of bovine thymic extract fraction C. Complete functional maturation of T lymphocytes in immunodeficient animals appears to require more than thymic extract stimulation of bone marrow cells or pre-T lymphocytes.     

INTERACTION BETWEEN INFECTIOUS BURSAL DISEASE VIRUS AND NEWCASTLE DISEASE VIRUS IN CHICKENS

The Australian strain of infectious bursal disease virus (IBDV), 002/73, affected the response of chickens to Newcastle disease virus (NDV). The titre of serum antibodies to NDV in chickens infected with IBDV was significantly lower than that of birds infected with NDV alone. It also appeared that IBDV affected NDV excretion from chickens as NDV was more frequently isolated from chickens infected with IBDV, IBDV infection did not alter the pathogenicity of NDV in chickens. This Australian strain of IBDV therefore appeared to be immunodepressive in one-day-old chickens.