ASSAY OF HYALURONIDASE 177 diverse sources and of a wide range of activity, is so high, is very strong evidence that all three tests are, in fact, measuring the activity of the same agent.In view of the contradictory reports that have appeared in the literature it is interesting to note, that when the viscosimetric assay is carried out at pH 7*0, in approximately physiological salt concentration, very good agreement is obtained with the results of skin-diffusing activity.SUMMARY 1.A method of assaying hyaluronidase is de- scribed, which depends upon the destruction by the enzyme of the power of a substrate-protein complex to form a typical 'mucin clot' on the addition of acetic acid.2. It appears that the destruction of the clotting power of the substrate is an early stage in its degradation, which can be deitected before any appreciable fall in viscosity occurs.3. Sera which inhibit the diffusing and viscosity- reducing activity of these enzymes also inhibit the mucin-clot prevention reaction.Sera prepared against enzymes obtained from Cl. welchii and Vibrion aeptique are species-but not type-specific.Those obtained against streptococcal enzymes are group-but not type-specific.A serum prepared against diffusing factor from bull's testis inhibited this enzyme, but did not inhibit a testicular enzyme from the mouse, or any of the bacterial enzymes.4. Both the apparent pH optimum of viscosityreducing activity, and the titre of the enzyme, are markedly affected by the concentration and nature of salts in the system.5. Nine enzymes from various sources' have been examined for diffusing activity in the skin, by viscosimetry and by the mucin-clot prevention test.The conclusion is drawn that all three tests measure the activity of the same agent.
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John Humphrey (1943) studied this question.