1. Following intravenous administration of testes hyaluronidase in rabbits and dogs, there is a decrease in the level of the non-specific inhibitor of hyaluronidase in serum.
2. If a large amount of hyaluronidase is injected, the inhibitor level is reduced to zero and hyaluronidase may be present in serum for some time after the injection. The hyaluronidase activity of such samples of serum increases when the serum is incubated with papain.
3. Hyaluronidase activity is found in the livers of the injected animals in large amounts and this activity is increased considerably when the homogenate of this tissue is incubated with papain.
4. Intravenous administration of several proteases or venom produces a decrease in the serum inhibitor level. Intravenous administration of streptokinase produces such a decrease in rabbits but not in dogs.
5. There is a correlation between the depletion of the inhibitor from the serum and the occurrence of a slow, persistent depression of blood pressure upon administration of proteolytic enzymes.