and L were prepared in our laboratory. With few exceptions, all dilutions of toxin were made either in broth, serum,

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Summary 7 tetanal toxins have been bioassayed by 5 methods, namely: 1) Intracerebral injection in rabbits, 2) intracerebral injection in guinea-pigs, 3) intramuscular injection in rabbits, 4) intramuscular injection in guinea-pigs and 5) intramuscular injection in mice. The relative potencies of the 7 toxins were found to be different for each individual method. Conversely, the relative potencies as determined by the five methods were found to be different for each individual toxin. These findings show that toxins from various sources are qualitatively not identical. The lethal dose is determined not only by the number of toxin molecules per ml but also by the toxicity of each individual toxin molecule. Some theoretical implications of these findings are discussed.

In a previous communication (1) a new method for the determination of the coefficient of the distribution of antibodies between blood and tissue has been described. The method was based on a quantitative comparison of direct and indirect1 cutaneous tests with diphtheric and staphylococcal toxins and antitoxins. By this means, the coefficient of the distribution of antitoxins was found to be in the neighborhood of 22. All these experiments were carried out with horse-serum antitoxins. Recently Heidelberger and Pedersen (2), Goodner, Horsfall, and Bauer (3), and Schaffer and Dingle (4) have found with the methods of ultracentrifugation, ultrafiltration and the molecular-film technic of Langmuir, that antibodies in horse serum may have a considerably larger molecular weight and volume than the corresponding antibodies in rabbit serum. Actually this has been demonstrated, thus far, only for types 1 and 3 pneumococcal antibodies, whereas according to Schaffer and Dingle, types 5 and 8 pneumococcal antibodies have the same molecular size in horse and rabbit serum.