A review of research related to the learning effect of dynamic versus static visual displays in media-bnsed instruction is presented. The analysis reveals that the dynamic visual display (DVD) is generally more effective than the static visual display (SVD). However, the research findings do not consistently support the superior effect of DVDs. These conflicting findings seem to be related to the different theoretical rationales and methodological approaches used in various studies and suggest that the use of DVDs should be determined selectively. From the literature review and theoretical discussions about instructional functions of DVDs, we propose six instru~ional conditions under which DVDs can be effectively used. The conditions are for: (a) demonstrating sequential actions in a procedural task; 0a) simulating causal models of complex system behaviors; (c) explicitly representing invisible system functions and behaviors; (d) illustrating a task which is difficult to describe verbally; (e) providing a visual analogy for an absl~act and symbolic concept, and (f) obtaining attention focused on specific tasks or presentation displays. Finally, several important considerations for the design and presentation of DVDs are discussed.

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The action of oc-amylase is due to the fission of the m-1:4-glucosidic linkage in amylose and amylopectin. By confining the study to amylose and its fission products, complications arising from the presence of 1:6-glucosidic linkages are avoided. It is well known that the action of this enzyme is at first relatively rapid until the iodine colour disappears (achroic stage), this being usually attained in the case of amylose when about 20 % of the linkages have been split. The mixture now consists of short-chain fragments including maltose and glucose (Myrback, 1948;Bernfeld, 1951). A much slower reaction, in some cases only one-hundredth as fast, overlaps and succeeds the first one. In this the short-chain fragments are successively split until only maltose and glucose or sometimes maltotriose remain. According to Myrback ( ), Bernfeld (1951, Meyer & Bernfeld (1941), Meyer & Gonon (1951), Alfin & Caldwell (1949 and Roberts & Whelan (1951) all except the terminal linkages in Vol.56ATO5O6xAYLSS8 the substrate molecule are attacked. So far as malt ment as upwards of 1-0 % in the case of the malt ACTION OF oc-ANYLASES 87 Vol. 56

Suicide prevention is a growing health concern in America for many minority groups. Although experts agree suicide is associated with cultural practices and beliefs, there is limited evidence on how African American women cultural values and practices influence their low rates of suicide. This study explores cultural identity, Africultural coping strategies, and depression as predictors of suicidal ideations and attempts among African American female college students. It was hypothesized that suicidal ideations and attempts are negatively related to cultural identity and Africultural coping styles, but positively related to depression. One hundred and thirty-seven African American female students were administered a battery of measures assessing cultural identity, coping strategies, and suicidal ideations and attempts. Results revealed that Africultural coping strategies and depression emerged as significant predictors of suicidal ideation and attempts. Results are discussed in terms of African American culture as a buffer to possible suicidal behavior in African American women.

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