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1. Fractionation of aqueous ragweed pollen extracts with water-miscible organic liquids produces purification and concentration of the allergens of these extracts. 2. Fractionation of extracts, purified by the above treatment, with high concentrations of sulphate salts produces further purification and concentration of the allergenic factors.

1. The present methods of making pollen counts were found to be inadequate. 2. An instrument was devised and is here presented which gives a better conception of pollen abundance in the air. 3. The importance of the pollen count on the vertical slides is emphasized. 4. The buoyancy index is presented as a graphic means of determining the relative buoyancy of the various pollens.