l6 BRENT, MEDAWAR AND RUSZKIEWICZ 



Table IV 

 Extraction of dried antigenic sediments with lipid solvents: activity of 



LIPID extractives AND OF RESIDUES AFTER EXTRACTION 



All experiments A->C3H. Sensitivity tested by A-strain tail-skin grafts trans- 

 planted 3 or 4 days after the sensitizing injection and removed for scoring 7 days 



later, 



Expt. Dose*^ Median 



no. Preparation ('".?•) l-day survival score survival times 



445B Residue after extraction 3-3 75,10,5,0,0 — 



C Lipid extractive 3-3 (lOO, 100, 100, 100, 100) 11 days 



D Mixture ofB&C 3-3 75,50,0,0,0 — 



446B Residue after extraction 



C Lipid extractive 



D Mixture of B & C 



E Nil (control grafts) 



449D Residue after extraction 3 • 8 

 E As D but soluble matterf 3 • 

 F As D but insoluble 



matterf 

 C Lipid extractive 

 E Nil (control grafts) 



45 iB Untreated P205-dried 

 antigen 

 C Residue after extraction 

 D Lipid extractive 



* In terms of mg. dry weight PaO^-dried antigen per mouse, 

 t After centrifugation at 5000^ for 10 minutes. 



Heat stability 



A most unexpected result of our experiments on the thermo- 

 stability of sensitizing antigens was evidence that some fraction of 

 the sensitizing power of antigenic sediments survived exposure to 

 100° for from four to 12 min. The sediment was redispersed in 

 gas-free water and heated under an atmosphere of nitrogen in a 

 boiling water bath. As with the residues of lipid extraction, 

 antigen so treated had no power to absorb the homologous iso- 

 agglutinins, but it retained a certain low but well-defmed sen- 

 sitizing power (Table V), predominantly in the insoluble fraction. 



