Two experiments tested the hypothesis that elderly adults conduct less elaboration of information to be learned than young adults. In Experiment 1, young and elderly adults were tested for free and context-cued recall of target words embedded in sentences ending in relevant (precise) or irrelevant (imprecise) elaborations. In Experiment 2, young and elderly adults were tested for recall of words in sentences for which relevant or irrelevant elaborations were provided or sentences for which relevant or irrelevant elaborations were generated by the participants. They were also tested for memory of the elaborations themselves. Elderly adults showed as much benefit from the provision of relevant elaborations as young adults but were less likely to generate relevant elaborations. The results reflect age-related differences in elaborating stimulus words in terms of previous knowledge and in encoding specific attributes of sentence contexts.

To test the hypothesis that elaboration of information declines with advancing age, young and elderly adults were tested for incidental recall of target words in base sentences, sentences for which precise (relevant) or imprecise (irrelevant) elaborations were provided, or sentences for which precise or imprecise elaborations were participant-generated. Age differences were greater when participants were instructed to generate precise elaborations than when they were provided precise elaborations, and elderly adults generated fewer precise elaborations than young adults. Results were discussed as reflecting the pervasiveness of elderly adults' difficulty in constructing effective elaborations.

Since the electrokinetic properties of a particle depend entirely upon the particle's surface, microscopic electrophoresis of dissociated cells can yield information about the cellular surfaces. Dissociated heart ventricle and liver cells from five-day chick embryos as well as neural retinal cells from seven-day embryos have been examined electrophoretically over a wide pH range and the pH-net surface charge density relation for each type of cell has been determined. Under the conditions selected the cells show differences with respect to these relations which appear to reflect differences in the molecular composition of the cells' surfaces.Since intercellular adhesion may occur through bivalent cation bridges with calcium being the cation most likely to be involved, the suppression of surface charge density by means of calcium ions at physiological concentration has been determined at physiological pH for heart ventricle, liver, neural retinal, and back epidermal cells. The degree of charge suppression, which varies among cells of different types, can be correlated with the apparent cellular adhesiveness as judged from sorting out behavior in some but not all cases.Dye exclusion, the ability of cells removed from the eIectrophoresis apparatus to reaggregate, and the reversibility of pH effects and calcium effects have been used to try to detect damage to the cells caused by experimental conditions. The results of these tests have seemed satisfactory.

No abstract

Sialic acids such as N-acetylneuraminic acid have been found at the surfaces of various cells. They may play a n important role in intercellular adhesion and hence in animal morphogenesis. This work demonstrates sialic acid at the surfaces of seven-day chick embryo neural retinal cells and its regeneration after enzymatic removal.Neural retinas were excised and dissociated with trypsin. The cells were incubated in a solution of Vibrio cholerae neuraminidase. The enzymatic treatment released sialic acid which was assayed by thg thiobarbituric acid method of Warren. The enzymatic treatment also reduced the cellular electrophoretic mobility from 1.1 to 0.4 X 10 cmlseclvoltlcm measured in 0.067 molar phosphate buffer at pH 7.5.Cells which had been treated with neuraminidase were cultured in a modified Eagle's minimum essential medium for up to 24 hours. During the period of culture, the replacement of surface material was observed i n two ways. First was the progressive return of electrophoretic mobility to the pre-neuraminidase level. Second was the progressive return of sialic acid at the cell surface to the original level. The latter was shown by second neuraminidase treatments and determinations of sialic acid released.Effects of neuraminidase upon the reaggregation of cells cultured on a gyratory shaker in Eagle's medium were investigated. Neuraminidase was not effective for dissociation of neural retina.