STUDIES ON TRANSPLANTATION ANTIGENS I9 



niance : soluble or semi-soluble antigenic extracts do not sensitize 

 when injected intravenously. 



Some small fraction of the sensitizing activity of cellular 

 extracts survives (i) their exposure to lipid solvents, and (2) 

 heating to 100°. (The matter extracted into Hpid solvents did not 

 sensitize.) Antigens treated in this v^ay did not absorb the homo- 

 logous humoral antibodies. One possible explanation of this fact 

 is that the antigens v^hich differentiate strain A from strains C3H 

 or CBA are a chemically heterogeneous assemblage. 



Acknowledgement 



The special expenses of this work and the stipend of one of us (M.R.) were 

 defrayed by grant E-3137 of the United States Pubhc Heakh Service. 



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