DISCUSSION 69 



tumour of the antibody donor genotype; then of course any antigens 

 secreted by the tumours just wouldn't matter. 



Dauies: We haven't any non-specific tumours derived from the 

 mouse strains we use. 



G. Kleif] : What is your antibody donor genotype ? 



Davies: We use C3H, BALB/c, ST/A and C57, and then we use all 

 the various combinations of these, and their hybrids. 



G. Klein: There are some C3H ascitic tumours growing non-specifi- 

 cally in foreign strains. We would be glad to send them to you. 



Eva Klein: It would also be possible to use specific tumours by pre- 

 irradiating the foreign recipients. 



Davies: I would be very pleased to have your help in this matter. 



Medawar: Dr. Davies, you refer to your product as antigenic, but I 

 don't recollect what tests you appHed. Do you mean that it excites the 

 formation of iso-haemagglutinins ? 



Davies: Yes, just that. For example, if we inject the C3H product 

 into BALB/c mice we get a haemagglutinating serum which can be 

 specifically inhibited only by the antigen injected, or by one having an 

 H-2 specificity in common with it. 



Medawar: Did you test for lysins ? 



Davies: No. 



Simonsen: By which route did you inject? 



Davies: Subcutaneously. 



Medawar: Among the differences between the activities of your 

 product and our own very much more impure one, you referred to 

 different resistances to drying and to ultrasonics. I don't think the tests 

 with ultrasonics are comparable, because they were done under very 

 different conditions. We expose whole cells suspended in water to 

 ultrasonic irradiation, and one knows, from analogy with the stabihty 

 of DNA and DNA protein, that material which would be degraded in 

 purer form may not be degraded when still in a "structural" form. 

 But the drying is a bit puzzling. We dry our material from a suspension 

 in water which is very rapidly frozen, and it is dried at a temperature 

 which isn't allowed to rise above — 5° c; our preparation treated in this 

 way retains, not all activity, but a high proportion of activity. Did I 

 understand correctly that your preparation loses all its activity on freeze 

 drying ? 



