Using the death of mice due to the growth of tumor homografts as an end point, the distribution and properties of a tumor homograft-promoting substance(s), the "enhancing substance," were studied.

Activity was most largely present in tumor and spleen tissues while that in the liver, kidney, and stomach was relatively slight.

Activity was widely distributed in fractions prepared from tumor. Although DNAP and crude RNAP fractions were active, activity could not be associated with either RNA or DNA. The fraction possessing the highest concentration of activity was a residue fraction which was insoluble in water or in dilute or strong saline solutions.

Extraction of lyophilized tumor with acetone or 3:1 alcohol:ether reduced, but did not eliminate, activity in the insoluble fraction. However, activity was completely lost after extraction with 80 per cent alcohol at room temperature.

Enhancing activity of a tumor fraction was irreversibly lost after exposure for 1 hour to a solution more acid than pH 5 or more alkaline than pH 9. Activity was completely lost after exposure to 50 per cent urea or 90 per cent phenol.

Activity was not altered by incubation with trypsin, hyaluronidase, DNAase or the receptor-destroying enzyme of V. cholerae, but it was decreased when trypsin or hyaluronidase was injected with the incubated tumor fraction.

Activity was rapidly destroyed by treatment with dilute solutions of sodium periodate at pH 7. Under similar conditions, treatment with KMnO4 resulted in less extensive destruction of activity while H2O2, K2Cr2O7, and NaIO4 previously inactivated by reaction with glucose had no apparent effect on activity.

These results are interpreted as indicating the presence of both carbohydrate and protein in the structure of the activity substance.

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