Compounds which have been found to be particularly advantageous where Y is a halogen atom and n is one, include: alpha-( 2-chlorophenyl)-N-lower alkyl nitrone, where the lower alkyl group contains from one to four carbon atoms; alpha-(3-chlorophenyl)-N-lower alkyl nitrone; and alpha-( 4-chlorophenyl )-N-lower alkyl nitrone, where the lower alkyl is as above described.