HAMSTER CHEEK POUCH SKIN HOMOGRAFTS IO3 



delaying the lymphatic vascularization among other things, an 

 attempt was made to increase the proportion of animals which 

 would accept pouch skin homografts for very long periods with 

 the aid of this agent. Hosts of pouch skin homografts were given 

 3 mg. of cortisone acetate subcutaneously at the time of operation, 

 followed by i mg. every 3rd day for three weeks. Although this 

 treatment was very effective in increasing the proportion of 

 animals that bore surviving grafts on the 30th postoperative day, 

 it failed to increase the proportion of long-term acceptors of these 

 homografts. 



Discussion and conclusions 



The evidence presented concerning the anomalously long sur- 

 vival of pouch skin homografts in hamsters is consistent with the 

 view that their exemption from the fate of skin, or other solid 

 tissue homografts that establish vascular connexions with their 

 host, stems from a failure of effective amounts of their antigens to 

 gain access to the hosts' seats of immunological response — 

 principally the regional nodes (Mitchison, 1954; Billingham, Brent 

 and Medawar, 1954). Various lines of evidence suggest that it is 

 at the level of the areolar connective tissue component of these 

 grafts that the physiological impediment must be sought. This 

 tissue does not interfere in any way with the acquisition by the 

 grafts of a rich blood supply, or prevent a normal skin graft from 

 getting one when a layer of areolar tissue — living or "devitahzed'* 

 — is interposed between it and a richly vascular bed. One possi- 

 bility, currently being investigated, is that the majority of pouch 

 skin grafts fail to develop an adequate lymphatic drainage for their 

 antigens to be able to stimulate the hosts. However, it must be 

 borne in mind that, in the case of orthotopic homografts of normal 

 skin, immunization of the host can apparently take place in the 

 absence of an intrinsic lymphatic drainage of the graft, the antigens 

 of the latter entering the host lymphatics in the graft bed (see 



