A comparative study of spreading factor and hyaluronidase in preparations from various sources revealed the following points of similarity and dissimilarity in the two reactions.

1. Similarities: (a) All preparations containing hyaluronidase also produced spreading. (b) Heating at 65° and 100°C. for 30 minutes produced a comparable effect on both reactions. (c) The demonstration of the presence of hyaluronic acid in skin offers a plausible explanation for the mechanism of spreading on the basis of hyaluronidase activity.

2. Dissimilarities: (a) No parallelism was observed in the degree of activity of spreading factor and hyaluronidase in the same preparations. (b) All preparations which produced spreading did not contain hyaluronidase. (c) Antisera to hyaluronidase preparations specifically and completely inhibited the activity of the homologous enzyme but did not inhibit the spreading factor in the same preparations.

The significance of the similarities and dissimilarities between the two reactions is discussed. It is concluded that while hyaluronidase may play a rôle in the spreading reaction the phenomenon is a complex one and cannot be explained on the basis of a simple chemical reaction.

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