A Simplified Apparatus for Photometric Analysis and Photomicrography

A significant advance in the technique of histology and cytology is the current trend toward the use of quantitative methods of studying microscopical preparations; in other words, of substituting an objective measure of absorption 'for expressions like "more basophilic," less Feulgeu-positive," etc. Among such methods are those which Caspersson has developed for determining the absorption spectrum of a small part of a cell, investigations which yield precise information as to the character and m o u n t of a naturally occurring substance (Caspersson, 1936, 1947). This technique is elaborate, and requires so much knowledge of a special field of physics that the average histologist is unlikely to be trained for such work. Fortunately, a much simpler procedure is possible if one knows the nature of the absorbing substance to be estimated, as for example, in the determination of hemoglobin in an erythrocyte (Thorell, 1947), in analysis for protein in a nucleus (Polllster and Ris, 1947), or in measurement of the dye in a stained nucleus (Di Stefano, 1948). In such cases, if the substance is in suflSciently high concentration, one can proceed much in an ordinary photometric chemical analysis and obtain information as to the amount of material in a small part of a cell, such as the nucleolus even though this amount is of the order of 10 -9 rag. Among the most abundant and physiologically important substances in cells are the nucleic acids and proteins; and these are the chief constituents responsible for staining an ordinary histological preparation. Indeed, it appears that with the common histological fixing methods a cell structure is mainly a nucleoprotein picture. Therefore, if one is to investigate the significance of cellular structure, an analysis for nucleic acids and proteins is probably the most valuable quantitative cytochemical study which can be undertaken. Recently Pollister and Ris (1947) have described briefly some procedures and an apparatus for nucleoprotein determination in cytological preparations. These are considerably simplified, and experience has shown that their use can be acquired readily by a worker who is trained in histology or cytology. Since then, the photometric apparatus, designed for use with the Photovolt photometer, has been much improved, especially in 567