This test quantitatively measures the presence of metabolic byproducts produced by the unidentified strain, by changing the color of the indicator broth within each separate plate well. The broth contains specific substrates, which are altered by the organism’s metabolic byproducts, thereby, altering the pH of the broth, producing a color change. By using a known antiserum, which is selectively added to chosen wells, then adding the unknown cultures, if the antiserum inhibits the growth of the bacteria, there will be fewer byproducts produced, and therefore, a different coloration will result when compared to a well containing a thriving species, unaffected by the antiserum.