from examination of table 4 the substances under examination generally have an acute oral toxicity which is greater than that of the chosen reference compounds however this toxicity is relatively low and of no practical importance considering the doses envisaged for human use mutagenesis test with metabolic activation on histidine strains of salmonella typhimurium by the ames method the capacity for reversing the histidine mutation which is peculiar to the ta 100 strain was measured this strain being recommended for chemio therapeutic screening in that it has a resistance factor r ta 100 is a carrier of a mutation caused by the substitution of a pair of bases the method used is that described by ames et al mutation res 31 1975 347 364 the results obtained are shown in table 5 which gives the maximul value of revertants per plate obtained for the various concentrations tested range of from 15 62 to 1000 u03bcg plate value which allows good descrimination between the experimental value and the background of the control which is about 100 revertants per plate table 5 ______________________________________mutagenic activity in the ames test in vitroon salmonella typhimurium ta 100 index of relative mutagenic power revertants plate compound compound max value metronidazole ______________________________________example 1 780 0 17example 3 1400 0 31example 4 780 0 17example 6 510.