Abstract: An imaging system and display thereof utilizes a set of overlapping picture elements of varying tonalities. A set of tones is provided by picture elements of differing sizes, of differing density of graphic design, and by the use of first and second colors of differing proportions on each of the picture elements of a set of picture elements. The appropriate tones are selected by producing a coarse half tone image of a subject, and then approximating the elemental regions of the half tone image by elements of the set of picture elements. The selected elements are positioned on a substrate of the display at locations corresponding to the sites of a regular grid.

Abstract: A method of purifying a protein-reaction mixture to obtain carboxypeptidase G.sub.1, which method comprises: passing the mixture through a column containing support material, such as carboxymethyl cellulose, under pH conditions such that the carboxypeptidase G.sub.1 is preferentially and selectively bonded to active sites on the support material in preference to other protein materials of the mixture; displacing the bound carboxypeptidase G.sub.1 by an eluant, such as a glutamate, which has a greater affinity for the carboxypeptidase G.sub.1 than the support material; and recovering from the column a mixture of the eluant and the carboxypeptidase G.sub.1.