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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.

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