96 R. E. BILLINGHAM AND WILLYS K. SILVERS 



Table III 

 Fate of second-set pouch skin homografts* 



* In these tests the hosts belonged to the M.H.A. or L.S.H. strains; the donors belonged 

 to the C.B. strain. 



t All second-set grafts were transplanted either 2-4 weeks after breakdown of the 

 primary graft was complete, or after a host had borne its primary C.B. graft in a healthy 

 condition for 50-90 days. 



ij: In three of these animals rejection of the second graft was soon followed by rejection 

 of the primary graft. Two animals were unique in that, despite rejection of their second- 

 set grafts, their primary grafts remained perfectly healthy. 



(3) Preliminary analysis of the anomalous behaviour of 

 pouch skin homografts 



Evidence that homografts of cheek pouch skin are not abnor- 

 mally resistant to transplantation immunity is forthcoming from 

 the fmding that long-established, healthy, pouch skin homografts 

 are usually destroyed within one or X^sro v^eeks following: (i) 

 transplantation to their hosts of grafts of homologous normal skin 

 from the original donor strain, of much smaller size than the 

 estabhshed pouch skin graft. The mode of rejection of these 

 sensitizing grafts was that of "first-set" homografts (Medawar, 

 1944), indicating the failure of the pouch grafts to sensitize their 

 hosts; or (2) the injection of the host intraperitoneally or intra- 

 venously with a relatively low dosage of homologous leucocytes 

 — as few as i million were effective — prepared from the buffy 

 coat of blood obtained from members of the original donor 

 strain; or (3) by the intradermal injection of bone marrow cells 

 (see Table IV). These fmdings leave no doubt as to the normal 

 susceptibility of pouch skin homografts to a state of sensitization 

 eUcited by proxy. In all cases where rejection was procured in 



