[M. L. Snyder (1907–69), American bacteriologist] A colorimetric test for evaluating caries activity or susceptibility. It is based on the rate of acid production by acidogenic micro-organisms e.g. Lactobacillus in a glucose medium using bromocresol green as an indicator. The glucose medium is inoculated with a saliva sample; any lactobacilli present will ferment the glucose, forming lactic acid and thereby lowering the pH. A rapid colour change from blue-green to yellow due to the pH change is claimed to indicate a susceptibility to the formation of dental caries.