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An early proliferative response follows the mixing of homologous spleen or lymph node suspensions obtained from two unrelated rabbits. The rate of incorporation of radioactive thymidine has been used as a quantitative measure of this response. Thymus cells do not respond to homologous cell suspensions but may on occasion serve to stimulate the response in homologous spleen or lymph node cells. Homologous erythrocytes or autologous tissues do not stimulate a response. No response occurs if the two cell populations are separated by a Millipore membrane. Autoradiographic studies have established that 1 to 2 per cent of the intial cell population is involved in the response and they are large undifferentiated cells by the time they can first be identified as responders. There was no morphological evidence of any cellular interaction and the viability of mixed suspensions was not measurably different from that observed in separate suspension. Simultaneous additive responses could be obtained to homologous cells and to antigen when cell suspensions from immunized rabbits were used. The interaction of the cell populations from the two rabbits did not appear to suppress the response of each to antigen. The speed and magnitude of the response were in everyway comparable with the secondary response of cell suspensions from immunized rabbits exposed to the immunizing antigen. No evidence was obtained of any enhancement of the response to homologous cells by prior immunization with homologous tissues, but the possibility that it had occurred was not rigidly excluded.

The technique of isolated liver perfusion has several unique features as an investigative tool for the study of hepatic physiology and biochemistry. These include the exclusion of non-hepatic tissues, the maintenance of intact cellular membranes, and the ability to control and reproduce more precisely the experimental hepatic environment than is possible in an entire animal. This investigative team has developed an isolated bovine liver peffusion preparation that is reproducible, bacterially sterile, and capable of continuous functional performance for extended periods of time.The use of a large mammal, such as the bovine calf, as the experimental animal has other useful characteristics; the large liver permits serial tissue sampling, yielding specimens of generous size. The large volume of perfusate, with little intrahepatic accumulation, allows frequent generous sampling of this medium. The use of autogenous blood as the perfusate avoids interaction between foreign proteins which could occur if blood were pooled from several homologous donors.The technique of perfusion reported herein permits simultaneous and independent perfusion through the hepatic artery and portal vein, and repetitive sampling of liver tissue and the circulating perfusate without interruption of the perfusion.This report describes the characterstics of this preparation as experienced in over 90 separate perfusion experiments.