R. S. DE ROPP 



389 



terin. A total dosage of as little as 0.05 ng. of these substances was suffi- 

 cient materially to reduce tumor growth (17). At low dosage levels the in- 

 hibition could be partially reversed by a one per cent solution of folic 

 acid. It is not yet possible to tell whether this inhibiting action is dif- 

 ferential, that is, whether it affects the tumor cells without interfering 

 with the growth of healthy tissue. 



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