This experiment was designed to examine the external validity of the standard mock-crime procedure used extensively to evaluate the validity of polygraph tests. The authors manipulated the type of mock-crime procedure (standard vs. a more realistic version) and the time of test (immediate vs. delayed) and examined their effects on the validity of the Guilty Knowledge Test (GKT) and the recall rate of the relevant items. The results indicated that only the type of mock-crime affected the 2 outcome variables. The realistic procedure was associated with a lower recall rate and weaker detection efficiency than the standard procedure. However, these effects were mediated by the type of GKT questions used. Practical implications of these results are discussed.

A simple method for studying the chemotactic responses of the plasmodium of Physarum polycephalum was designed. A positive chemotactic response was detected towards the sugars D-glUCOSe, lactose, D-maltose and D-galactose, the amino acids L-leucine, L-serine and DL-phenylalanine, and the nucleotide uracil. The significance of chemotaxis in Physarum is discussed. I N T R O D U C T I O NThe fascinating phenomena of chemotaxis, movement and plasma shuttle streaming in plasmodia of myxomycetes have attracted the attention of many scientists for almost a century (Pfeffer, 1883;Kamiya, 1959; Carlile, 1970;Chet & Mitchell, 1976).In recent years, analysis of receptors and a better understanding of their mode of action in bacteria has been achieved (Adler, 1975). The role of chemotaxis in cell aggregation of the cellular slime-mould was comprehensively reviewed by Bonner (197 I) and his collaborators. The plasmodium of acellular slime-moulds shows a similar response towards chemical attractants (Konijn, 1973). There has been much interest in the biochemical and physiological analogies between the plasmodium of acellular slime-moulds and the muscular systems in vertebrates (Kessler, 1972;Komnick, Stockem & Wohlfarth-Botterman, 1973).In this paper we describe a system developed to measure chemotactic responses towards carbohydrates, amino acids and nucleotides. M E T H O D SMicroplasmodia of Physarum polycephalum (Madison strain M~C ) were grown in 250 ml flasks containing 20 ml semi-defined nutrient solution prepared according to Daniel & Baldwin (1964)~ and incubated for 48 to 72 h at 24 "C in darkness on a reciprocal shaker (70 cycles min-l). The microplasmodia were centrifuged at 150 g for 5 min, and washed twice in salt solution (Daniel & Baldwin, 1964). Samples (0.1 ml) of microplasmodia were placed on sterile medium containing 0.02 M-phosphate buffer (pH 6.4) and 2 % (w/v) agar (Difco). Within 12 h fusion of the microplasmodia took place, and after 24 h 1.0 x 0.5 cm pieces of plasmodium were cut and transferred to the test system.The 'star' configuration of the test system was cut in the agar (12 ml0.02 M-phosphate buffer pH 6.4 and I % agar) as shown in Fig. I. Test substance (0.1 ml, 0.05 M) was applied to one of the four holes (8 mm diam.) cut in the agar. The other three holes contained the control buffer solution.The glucose gradients formed in the agar were measured by covering its surface with 5 ml of solution containing I mg ~,3,5-triphenyltetrazoliurn chloride ml-l (Sigma) for 10 min in darkness (Stahal & Kaltenbach, 1965). The reagent was washed off with water. Strips of agar (I x 5 cm) were cut and placed on microscope slides and the colour intensity was recorded by a Varian spectrophotometer model 635 (Varian Techtron, Mulgrave, Australia) at 600 nm. This test showed that a gradient of I to 2 pg ml-I mm-1 between 40 to 60pg glucose ml-l was sufficient for a positive chemotactic response. Such a gradient was reached 30 mm from the hole containing the attractant after 24 h of diffusion. A positive chemot...