Il6 DISCUSSION 



immunological sense is hardly defensible. Although Syrian hamsters 

 respond vigorously to various heterologous antigens, it is peculiarly 

 difficult to induce them to make antibodies against isoantigens; we have 

 obtained humoral isoantibodies from hamsters, but only after pro- 

 longed immunization and then not regularly. 



Lawrence: What is their response to bacterial antigens and do they 

 develop delayed allergy in the way the guinea pig does ? 



Hildemann: I beheve Stanley Cohen has produced typical tuberculin 

 sensitivity in the hamster. 



Billingham: And of course the homograft reaction in hamsters to 

 orthotopic skin grafts is highly conventional. 



Dr. Hildemann has just told us how difficult it is to demonstrate 

 humoral isoantibodies in hamsters following immunization with homo- 

 logous cells. This led me to wonder whether the hamster hasn't pro- 

 vided us with a sort of natural experiment to differentiate between the 

 roles of cellular and humoral immunity in skin homograft rejection. 

 If you put on a skin graft and it's rejected quite promptly you get no 

 evidence of any humoral antibodies at all in the hamster. Is this valid 

 evidence in trying to settle this much vexed question ? 



Medawar: Is it absence of antibody or undetectabihty of antibody ? 

 One doesn't know. 



Simonsen: May I return to this "slime"? Could you give us more 

 details about the treatment with hyaluronidase ? 



Billingham: We injected the enzyme into established homografts to 

 try to promote their rejection. W^eekly injection for many weeks had 

 no effect. 



Simonsen: But did you check to see whether the hyaluronidase 

 actually broke down some of the mucoid substance in the pouch ? 

 Have you, for example, done metachromatic staining before or after 

 treatment with hyaluronidase? Perhaps the mucoid substance is not 

 proper hyaluronic acid but some other mucoid substance. The fact, as 

 you mentioned before, that the frozen-dried pouch or slime layer 

 would also work seems to me a very strong indication that it is a sort 

 of chemical protection. 



Medawar: I don't see why. Perhaps this frozen and thawed slime 

 simply won't support the penetration of lymphatics. 



Eichwald: If you are unable to penetrate the slime with hyaluronidase, 



