Experiments given in this paper have shown that 4-arsonophenylazoproteins possess marked anticoagulant activity both in vivo and in vitro. Mice and rabbits given moderate amounts of the arsenic azoprotein, for example, often bled to death from injuries that proved trivial in control animals, and their blood remained liquid during many hours' postmortem even when left in contact with transected tissues, fibrinolysis having no part in the outcome. So, too, the addition of minute amounts of 4-arsonophenylazoprotein to plasma procured from citrated rabbit or human blood greatly prolonged the time required for clotting after recalcification.

Other arsenic-containing compounds,—for example, those in which arsenic

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was joined to amino acids or peptides through the azo linkage, or to proteins through couplings other than the azo linkage,—were largely devoid of anticoagulant and antilymphoma effects. The findings as a whole show clearly that the structural requirements for anticoagulant and antilymphoma effects are: (a) possession of negatively charged arsonic or arsinoso groups, (b) large molecular size (protein), and (c) linkage of arsenic-containing groups to protein through the azo bond.

Two acidic azoproteins that were devoid of arsenic,—namely 4-carboxyphenylazoprotein and 4-sulfonophenylazoprotein,—were also found to have marked anticoagulant effects in vitro, but they had no inhibitory action against cells of Lymphoma 6C3HED in vivo, even when they were given to mice in maximum tolerated amounts. The essential part played by arsenic in the antilymphoma activity of arsenic azoproteins was further emphasized by the action of dimercaprol (BAL) in preventing the antilymphoma effects of 4-arsonophenylazoprotein on Lymphoma 6C3HED cells in vivo.

In an associated paper the anticoagulant and antilymphoma effects of 4-arsonophenylazoproteins are studied further, and consideration is given to the ways in which these effects may be brought about.

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