The article by Daniel Mazia, Philip A. Brewer, and Max Alfert discusses the application of the mercuric bromphenol blue (Hg-BPB) staining technique in cytology for the demonstration and measurement of protein distribution and concentration. The authors review various techniques used in cytological protein staining, noting that none has been widely adopted for both morphological detail resolution and relative protein concentration measurement. They introduce the Hg-BPB reagent, which has been widely used for detecting protein spots in chromatographic and electrophoretic techniques, and describe its application in cytological material. The experimental section details the preparation of tissue samples using common cytological fixatives, the staining procedure, and the washing and conversion steps to ensure optimal staining. The authors emphasize the importance of thin preparations due to the intense staining intensity of the Hg-BPB method. The results section presents qualitative and quantitative data. Qualitatively, the Hg-BPB staining is shown to be effective in various materials, including cilia, mitotic figures, lampbrush chromosomes, and amoeba. Quantitatively, the authors test the validity of Beer's Law and Lambert's Law for the Hg-BPB staining, demonstrating that the method accurately measures protein concentration. They also compare the Hg-BPB reaction with other methods, such as the Millon reaction, and discuss the specificity and quantitative significance of the Hg-BPB staining. The discussion highlights the advantages of the Hg-BPB method, including its ability to stain a wide range of proteins and its potential for estimating total protein concentration. The authors suggest that the method can be useful for comparing basic protein to total protein and for studying the distribution of protein groups through different mechanisms. In conclusion, the Hg-BPB staining technique is presented as a valuable tool for cytologists interested in protein distribution and concentration, offering both qualitative and quantitative advantages over existing methods.The article by Daniel Mazia, Philip A. Brewer, and Max Alfert discusses the application of the mercuric bromphenol blue (Hg-BPB) staining technique in cytology for the demonstration and measurement of protein distribution and concentration. The authors review various techniques used in cytological protein staining, noting that none has been widely adopted for both morphological detail resolution and relative protein concentration measurement. They introduce the Hg-BPB reagent, which has been widely used for detecting protein spots in chromatographic and electrophoretic techniques, and describe its application in cytological material. The experimental section details the preparation of tissue samples using common cytological fixatives, the staining procedure, and the washing and conversion steps to ensure optimal staining. The authors emphasize the importance of thin preparations due to the intense staining intensity of the Hg-BPB method. The results section presents qualitative and quantitative data. Qualitatively, the Hg-BPB staining is shown to be effective in various materials, including cilia, mitotic figures, lampbrush chromosomes, and amoeba. Quantitatively, the authors test the validity of Beer's Law and Lambert's Law for the Hg-BPB staining, demonstrating that the method accurately measures protein concentration. They also compare the Hg-BPB reaction with other methods, such as the Millon reaction, and discuss the specificity and quantitative significance of the Hg-BPB staining. The discussion highlights the advantages of the Hg-BPB method, including its ability to stain a wide range of proteins and its potential for estimating total protein concentration. The authors suggest that the method can be useful for comparing basic protein to total protein and for studying the distribution of protein groups through different mechanisms. In conclusion, the Hg-BPB staining technique is presented as a valuable tool for cytologists interested in protein distribution and concentration, offering both qualitative and quantitative advantages over existing methods.