104 R- E- BILLINGHAM AND WILLYS K. SILVERS 



McGregor and Conway, 1956; Scothorne, 1958; McKhann and 

 Berrian, 1959). 



We must now consider to what extent the pecuUar immuno- 

 logical properties of cheek pouch skin homografts, transplanted 

 to the walls of hamsters* chests, are related to the immuno- 

 logically privileged nature of the site afforded to grafts of foreign 

 origin by the intact pouches. The success of central inlays of 

 homografts of normal skin in established pouch skin grafts on the 

 chest suggests that a common mechanism may be involved. 

 This belief is strengthened by our fmding that survival of similar 

 inlay grafts of rabbit skin heterografts is greatly prolonged in 

 cortisone-treated hamsters as compared with that of orthotopic 

 skin heterografts in similarly treated hosts. Furthermore, it has 

 been found that a DBA mouse strain lymphosarcoma grows more 

 rapidly when injected into established cheek pouch isografts on 

 the chests of cortisone-treated hamsters than when injected 

 intradermally. However, Shepro, Eidelhoch and Patt's (i960) 

 recent demonstration that grafts of malignant melanomata, of both 

 homologous and human origin, implanted into hamsters' cheek 

 pouches soon provoke changes indicative of an immunological 

 response, in the cervical nodes (which must therefore be pro- 

 visionally regarded as the regional nodes of the cheek pouches), 

 and to a lesser extent in the contralateral nodes and spleen, may 

 indicate that a more complex or different mechanism underlies 

 the privileged status of the intact pouch as a graft site. 



Phenomena which may possibly be cognate with the prolonged 

 survival of pouch skin homografts on hamsters' chests include : 

 (i) the indefinite survival of a significant proportion of early 

 foetal skin homografts transplanted orthotopically to adult 

 rabbits reported by Toolan (1958). In discussing the exemption 

 of these grafts from rejection this worker attached considerable 

 significance to the incomplete maturation of the formed elements 

 of their connective tissue ground substance. Although we have 

 been unable to confirm Dr. Toolan's findings in rabbits, in each 



