Rejection of first-set allografts in field collected Diemictylus viridescens is manifested by: ( 1 ) secondary vessel dilation (about 17 days), (2) hemostasis (about 20 days), ( 3 ) hemorrhage (about 23 days), and (4) eventual melanophore death (from 28 to 40 days). All these events were somewhat variable with respect to the time of onset, intensity, and duration. Histologically, these changes that distinguished allografts from autografts were paralleled by: ( 1 ) an increasing infiltration of small lymphocytes without graft destruction (secondary vasodilation), and (2) a stronger infiltration of lymphocytes concomitant with glandular death (hemostasis, hemorrhaging, and melanophore death). Although this pattern of rejection was the norm, several examples of long-term graft survival were encountered.When 28 days separated the transplantation of single first-and second-set grafts, a clear anamnestic response was elicited although circulation was re-established in 58% of the secondary transplants. Specificity of the second-set response was demonstrated.Single second-set transplants grafted ten days after single first-set grafts were not rejected in an accelerated fashion; rather such grafts often survived for a few days longer than the first-set grafts transplanted to the same host.The rejection of allografts from donors of different sexes transplanted to hosts of both sexes did not reveal any sexual dimorphic response. The site of trans. plantation (flank or throat) did not alter the timing or sequence of the rejection pattern.For about two weeks following allogeneic skin transplantation at 23°C in the adult newt, Diemictylus viridescens, the grafts appear quite healthy and do not exhibit any indications of incompatibility (Cohen, '66a). However, Erickson ('62) and Cohen ('65a) found that by 3 to 4 weeks after transplantation, such allografts exhibited hemostasis, hemorrhaging, and lymphocytic infiltration -events which indicated progressive rejection. In his experiments involving multiple skin grafts., Erickson surmised that this rejection was immunologically mediated for he reported an accelerated reaction to second-set transplants made ten days after first-set grafts. Pizzarello and Wolsky ('60) also observed allograft rejection in newts but reported that single skin allografts from male D. viridescens donors were rejected during the first post-operative week while grafts from female donors survived for more than J. EXP. ZOO^.., 163: 173-190. 100 days. Erickson ('62), however, could find no evidence of sexual dimorphism in allograft rejection for 14 intersexual and 19 intrasexual grafts, although no details regarding the number of grafts per host or the sex of the donors involved were given. The possibility that donor sex played a role in determining the fate of skin allografts in the newt was further investigated by Squadroni and Wolsky ('62) who concluded that when a male and female skin graft were placed on the same host, the former graft was quickly rejected while the latter was not. Lymphocytes...
