The results of a series of quantitative turbidimetric precipitin-tests when plotted according to a three-dimensional scheme define the extent of the precipitin-reaction under study and describe the quantity of reaction in terms of the amount of precipitate formed over the range of visible antigen-antibody combination. The results of the ring-test methods and the method of optimal proportions when placed on the three-dimensional surface are observed to be of far less value in the description of

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... he precipitin-reaction than is the quantitative turbidimetric method, for the information they yield may be not only fragmentary but sometimes misleading. Further implications of the three-dimensional expression of the results of precipitin-studies are under investigation.