Abstract: This invention provides compounds of the general formula I ##STR1## wherein R.sup.1 and R.sup.2 independently represent groups selected from the group consisting of straight chain alkyl groups; branched chain alkyl groups; aryl groups; optionally substituted aryl groups and the groups required to complete a ring system together with the sulphur atom;R.sup.3 and R.sup.4 independently represent groups selected from the group consisting of hydrogen; straight chain alkyl groups; branched chain alkyl groups and optionally substituted aryl groups;R.sup.5 and R.sup.6 independently represent groups selected from the group consisting of alkyl groups and the groups required to complete a heterocyclic ring together with the nitrogen atom; the groupR.sup.7 represents a group selected from the group consisting of hydrogen; straight chain alkyl groups and branched chain alkyl groups;X represents an anion of a physiologically acceptable acid andn represents a number selected from the group consisting of 0 and 1.