Aggregates of mildly denatured bovine serum albumin (BSA) present antigenic determinants which are not found in native or denatured but unaggregated BSA. Antibody against these determinants appears early and often transiently in rabbits immunized with denatured or native BSA emulsified in Freund's incomplete adjuvant. Using agglutination of tanned red cells, coated by exposure to native or denatured BSA, to detect and measure antibody activity against BSA, it was shown that adding trace amounts

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... of gelatin to the coating solution significantly reduces the sensitivity of the test. This effect is related to gelatin's highly efficient adsorption to tanned red cells. The degree of reduction in sensitivity varies with the antiserum tested.