1. The factor responsible for the spreading property of testicle extracts was found to be soluble in water, in salt solution, and in acid media. It is relatively stable at high hydrogen ion concentrations, and it is not precipitated or inactivated by hydrochloric acid up to pH 2.0. The spreading substance is not soluble in acetone, ether, alcohol, chloroform, or pyridine. It is inactivated by crystalline trypsin and pepsin at the optimum pH of action of these enzymes. It is not attacked by a crystallized carboxypolypeptidase. The substance does not pass semipermeable membranes which retain proteins. The color tests for proteins are positive. At least 14.2 per cent of the fraction isolated is nitrogen. Taken together these properties are strong evidence that the testicular factor is a protein.
2. A method for the preparation of the spreading factor in relatively pure form is presented and discussed.
3. In addition to the spread, concentrated solutions of the testicular factor are shown to produce a condition of the skin having the characters of edema.