Relation of Survival Time to Implantation Time of Second Set Skin Homografts in the Rat. ∗

Abstract

Summary and Conclusion

1. Relation of survival time to implantation time of second set skin homografts in the rat was studied. 2. Second set homografts implanted simultaneously with, or 5 days after the first set graft, develop an active hemal circulation and are rejected simultaneously with first set graft. 3. Second set homografts implanted 6 or 7 days after first set graft never become re-vascularized and are considered to survive for zero days. 4. Second set homografts implanted 8-30 days after first set graft develop an active hemal circulation and survive for a mean time of 5.1 days. 5. Second set homo-grafts implanted 60 days after first set graft show a normal first set survival time of 8 days. 6. There is no significant difference in survival time of second and third set grafts when third set is implanted 7 days after the second set graft. 7. It is concluded that temporal sequence in accelerated breakdown of second set skin homografts is suggestive of an immunological mechanism triggered by the host's contact with the first set graft. This is in agreement with Medawar's theory of acquired immunity.