HAMSTER CHEEK POUCH SKIN HOMOGRAFTS 95 



produce grafts having a wart-like or papillomatous appearance, 

 were conspicuous features. As a group, even the healthy homo- 

 grafts showed more tendency to contract than did the isografts. 

 Examination of biopsy specimens from long-established, healthy- 

 looking pouch skin homografts frequently revealed local areas of 

 mild lymphocytic infiltration in the graft dermis which may have 

 been indicative of a feeble, but completely ineffective, reaction on 

 the part of the host (see also Cohen, 1961). There was no evidence 

 that the size of these pouch skin homografts influenced their fate. 

 The prognosis for long-term survival of very large grafts was 

 certainly not inferior to that for small grafts. 



These unexpected prolongations of survival of cheek pouch 

 skin homografts, in the case of each of the three different donor/ 

 recipient strain combinations tested, strongly suggested that 

 homografts of pouch skin are themselves privileged for one reason 

 or another. Either (a) their capacity to sensitize their hosts is 

 abnormally feeble, or (b) they are much less susceptible to a state 

 of sensitization than skin homografts. Experimental evidence 

 that may be considered to refute this second possibihty outright 

 includes : (i) the finding that pouch skin homografts are consistently 

 rejected in a peremptory manner if transplanted to hosts which 

 have previously rejected homografts of ordinary skin from the 

 same donor strain; and (2) the fact that hamsters which have 

 rejected homografts of pouch skin soon reject subsequent grafts of 

 pouch skin from the same donor strain, whereas most hamsters 

 bearing long-established, healthy grafts of homologous pouch 

 skin will usually accept a second pouch skin homograft trans- 

 planted to the opposite side of their chest (see Table III). Two 

 out of 18 hamsters bearing healthy primary homografts of 

 pouch skin of at least 50 days standing rejected secondary grafts 

 after 27 and 40 days respectively, yet their primary grafts re- 

 mained healthy. This paradoxical state of affairs may simply 

 reflect the ability of estabhshed grafts to withstand low levels of 

 sensitization. 



