Summary. Surgical techniques are described for ihe long-term collection of lymph from hoih prescapular efft-reni lymph ducts of focial lambs in utero. Lymph duels iti t'oeial lambs 95 lo 136 days posi-concepiion were cannulated wilh a high rate of success. Lymph flow from [he cannulas was not compromised by deliberate primary or secondary challenge of the lymph nodes with a wide variety of antigens, and often continued for long periods afler the lambs were born naturally. The techniques allow cellular and humoral lymph-borne immune responses ol' foeial lambs lo auihentic primary atitigcnic challenge to be studied //(iiteri>, uncomplicated by any previous e>;perience of antigens. Loss of lymphocyios from the cannulated duels depleted the numbers of cells in the lymph, but lymph prolein conccniraiions were unaffected by lymph drainage.

Sumtnar).The canntilaied prescapiilar lymph node ol ihe locKil lamb wa>. challenged wiih killed Brucella abortus. Usuallv, boih effereni prcscapular ducts were cannulaied and one node Icfl as a control. Nodes were given primary or secondary challenges wiih doses of 10" -2 X 10'" brucella organisms and ihc lymph-borne response oT liic nodes followed.The tbeial lymph node produced ii vigorous Lcllular response lo ihc injecied brucella. reslricled to the challenged side. The loial cell output and, more strikingly, large celt output increased lo reach a peak value 4-5 days after challenge. Thi.s cellular response was seemingly dose-dependent.Ihc ouipiii Lil aiiiibiiijy afier a piiniarv ch a Men tie was delayed amsiderabK and could not bedetecled in the lymph uniil well afler the cellular response had subsided. Theconcentraiions or antibody produced were quite low and almost all meicapioeihanol-sensitive. With secondary cliallenges the outpiii of antibody occurred much more qiiiekly, in phase with ihe cellular response, and appreciable amounts ol' mercapioeihanol-resistani antibody were produced.Under exceptional circumstances, high titre, highly spcciliv antj-briicella antibody lias been produced in toetal lymph. The foetal lymph node provides a powerful tool tor further sludics of ihe ontogeny of the immune response, and might help elucidate the failure of newborn animals to respond lo some important bacicrial antigens.