Presentation format, other-person strategies, and cooperative behavior in the Prisoner's Dilemma

80 college students played a 50-trial Prisoner's Dilemma. Variables were manipulated at 2 levels each: (1) presentation format (matrix vs nonmatrix), (2) initial behavior of the confederate (hostile vs neutral), and (3) contingency of the confederate's choices (contingent cooperation vs noncontingent). Ss under the nonmatrix condition cooperated significantly more frequently than did Ss under the matrix condition and Ss playing with a confederate who behaved contingently cooperated more frequently than Ss playing with one who behaved noncontingently. Ss playing with an initially hostile confederate were at first more noncooperative than Ss playing with a neutral person but when the initially hostile confederate changed to a neutral strategy the difference between the 2 groups disappeared. None of the interactions were significant.

A new histochemical method for acid phosphatase by the use of 5-iodoindoxyl phosphate

5-Iodoindoxyl phosphate has been found to be a useful indigogenic substrate in the histochemical demonstration of acid phosphatase activity. Its superiority to other indoxyl phosphates is apparently due to a rapid oxidation of 5-iodoindoxyl to 5,5'-diiodoindigo in the acid pH range. A redox system of ferri-ferrocyanide enhances the oxidation and improves the localization. This method can be applied to calcium-formol-fixed tissues or to fresh frozen sections, although fixed tissues yield better results. The method is not recommended for the demonstration of enzyme activity in lipid-rich tissues because of the complexing property of lipids with 5,5'-diiodoindigo that results in crystal formation. The distribution of acid phosphatase activity with this method is generally similar to that obtained using azo dye methods.