A guanidine compound of the following formula (III): ##STR24## wherein X is sulphur or NH;Y is oxygen or sulphur; m is 1 to 4; n is 1 to 4;provided that when Y is oxygen, n is 2 to 4; R1 is a hydrogen or halogen atom or an alkyl radical of 1 to 6 carbon atoms; R2 is a hydrogen atom, an alkyl radical of 1 to 10 carbon atoms, an alkanoyl radical of 1 to 6 carbon atoms or an aroyl radical of 7 to 11