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ESTIMATION of microquantities of purines by paper chromatography was first suggested by Hotchkiss1. Later, detection by photographing with an ultra-violet source has amplified the method2. Tennent et al. 3 and others have designed adaptors for the Beckman spectrophotometer to enable direct estimation of the purines from paper chromatograms. This method requires costly instrumentation, and is time-consuming unless an automatic recorder is provided.

THE analysis of the protein composition of blood serum or plasma by means of zone electrophoresis on filter paper has stimulated interest in clinical laboratories throughout the world. In addition to numerous publications dealing with the applications of the technique in various pathological conditions, critical assessments of its validity and accuracy have appeared1–4, in which attention is properly directed to the limitations of the method from the point of view of the numerical evaluation of the separated protein fractions. It has seemed desirable to undertake a study of the accuracy and reproducibility of this method of protein analysis, using two of the most commonly employed protein-dyeing techniques.

It has been observed, and proved experimentally, that the nature of the paper surface has a considerable effect on the tone reproduction characteristics of halftone processes. It is concluded that any tone reproduction curve related to a halftone process is meaningless unless the type of paper to which it applies is specified in general terms.