Quantitative Criteria of Antagonism

The method of mixing equally toxic solutions furnishes the best criterion of antagonism, since we know at the outset just what effect each mixture must have provided there is no antagonism. Mixtures of two equally toxic solutions must have precisely the same effect on growth as the pure solutions themselves, provided that the effects of the salts are additive. If antagonism exists there is an increased growth in the mixtures. The amount of this increase, expressed as percentage of the growth obtained in the pure solutions, is the most satisfactory measure of antagonism. The most reliable results are obtained by the use of uniform material and by taking for measurement only such parts as come into immediate contact with the solution.