The present invention is concerned with the use of aniline derivatives of the general formula: ##STR1## wherein R1 is a hydrogen atom or a lower alkyl or aryl radical, R2 is a hydrogen atom or a lower alkyl radical which can be substituted by hydroxyl, amino, carboxyl, lower alkoxycarbonyl, lower alkanoylamido, aryl lower alkyl or aryl or by a group of the structure: ##STR2## in which R5 and R6 ha