1. Studies on a number of individual hog stomachs have shown that substances with blood group A activity cannot be obtained from all hogs. Of ten stomachs studied, only seven yielded products with blood group A activity. All ten purified preparations, however, showed identical properties with respect to nitrogen, reducing sugar, glucosamine, acetyl, and relative viscosity. Six of the seven active samples were of equal potency in precipitating anti-A; the seventh was slightly less active.
2. Preparations from random pools of hog stomachs, although possessing the same analytical properties, were of lower activity than those from individual active stomachs as determined by the microquantitative precipitin method.
3. An immunochemical method for estimating the absolute purity of the blood group A substance by determining the proportion of its glucosamine precipitated by excess anti-A was developed. Values of about 84 per cent for the purity of six of the seven purified active preparations from the individual hog stomachs were obtained.
4. The inactive products, unlike the active ones, did not stimulate the production of anti-A on injection into human beings and did not precipitate anti-A or inhibit hemagglutination of A erythrocytes by anti-A.
