One-bath trichrome staining: Investigation of a general mechanism based on a structure-staining correlation analysis

Summary Dye pairs of contrasting colours were selected from acid dyes of varied chemical characteristics. The 44 dye pairs were investigated in a one-bath trichrome staining system in which the dye-baths were strongly acid. Dye concentrations, concentration ratios and staining times were varied for each dye pair. Thirty dye pairs stained collagen fibres distinctly different colours to muscle cytoplasm, while 14 dye pairs gave muddy, non-selective staining. Comparison of dye structures showed that in selective pairs the larger dye always stained the collagen fibres, with cytoplasm being coloured by the smaller species. With 28/30 of the selective dye pairs the differences in anionic weights of the dyes was > 200. However, in dye pairs giving non-selective staining, the anionic weights of the members of 13/14 of the dye pairs differed by < 200. As no other structural feature correlated so clearly with selectivity, it was concluded that the selectivity of one-bath trichromes is diffusion-rate controlled, involving the interaction of differentially permeable tissue sites (collagen being more permeable than muscle cytoplasm) with dyes diffusing at different rates (large dyes slower than small). In keeping with this, lengthening staining times reduced staining selectivity. The rate control mechanism suggested a rational trouble-shooting guide for one-bath trichromes, encompassing such practical factors as dye concentration, embedding medium, fixative, dye-bath pH, section thickness and staining time.     

The Effect of Preliminary Treatment (Fixing Fluids) on Staining Properties of the Tissues

As was reported in a previous paper,¹ staining properties depend on the chemical composition of the tissues and on the strength of the dyes themselves. Applying mixtures of basic and acid dye on tissues (methylene blue, eosin Y) at different pH-values, it is possible to find differences in the isoelectric points of the nuclei and cytoplasm of different tissues. For example, the nucleus of polymorphonuclear cells of the blood consists of the most acid protein, with an isoelectric point around pH 2.5, while the nucleus of lymphatic tissues has an isoelectric point of about pH 4.0, and that of connective tissue about pH 3.4.

With a knowledge of the above, a constant method of staining at various pH-values was used to study the effect of different fixing fluids on the staining properties of the tissues. In this way it was found that many fixing fluids gave very stable compounds with tissue proteins, and that they almost permanently change the chemical composition (i.e. the staining properties of the tissues). In some instances, these changes can be easily explained from the regular chemical standpoint. For example, formalin forms inert compounds with amino groups of the amino acids of proteins and in this way it makes the tissue proteins more acid, i.e. it moves the isoelectric point of the proteins toward a lower pH-value. The same is true in the case of the polivalent acids. The bivalent heavy metals such as mercury, on the contrary, it is assumed, combine with carboxyi groups of amino acids and in this way move the isoelectric point of the proteins toward a higher pH.     

The Use of Buffered Solutions in Staining: Theory and Practice

The importance of pH in staining tissue is emphasized. The effect of pH upon the selectivity and intensity of staining with iron hematoxylin, malachite green, and eosin Y is considered. Many difficulties may be avoided by staining in the higher alcohols and directions are given for the preparation of buffer solutions from pH 1.2-8 in alcohol. The concentration of stains, time of staining, and order of staining are discussed for progressive and regressive staining. At pH 8 in 95% alcohol very few tissues stain with malachite green at a concentration of 1/1000 saturated. At pH 6 most cytoplasmic elements stain with malachite green at a concentration of 1/1000 saturated or with eosin Y at 1/250 saturated. As the pH is lowered more tissue elements stain until the nucleus is completely stained. This behavior is in accord with the theory of chemical combination of dyes with proteins, which states that proteins combine with basic dyes on the basic side of their isoelectric points and with acid dyes on the acid side of their isoelectric points. With hematoxylin stain the pH range is much shorter. A satisfactory hematoxylin stain is composed of 0.1% hematoxylin, 0.1% FeCl₃, and HCl to bring the pH to 1.2-1.6 in 80% alcohol. With this stain, which may be used immediately, the nuclei of most tissues begin to stain at pH 1.2 and much of the cytoplasm will be stained if the pH is raised to 1.4. The shortness of this effective pH range is thought to be due to the dissociation of the hematoxylin-iron-protein complex. The use of different dyes successively at different pH values, such as hematoxylin at 1.3, malachite green at 8, and eosin at 6, permits better differentiation of the tissue elements, and intelligent variations in the staining technic.     

Investigation of Thiazin Dyes as Biological Stains II. Influence of Buffered Solutions on Staining Properties

The effect of buffer solutions of varying reaction upon staining fixed sections with thionin, azures A, B, and C, and methylene blue has been studied. The buffer solutions were employed in one of three different ways: for pre-treatment of the sections, for post-treatment, or as solvents for the dyes. Regardless of the method of employing the buffer solutions it was found that the intensity of staining increased with increasing pH-values (a fact which is generally known to be true in the case of basic dyes). It is not certain whether this effect is due to varying the H-ion concentration or to altering the salt content of the solution, or to both. It was also noticed that there was one point where the staining intensify increased most rapidly. This point was either between pH 5 and pH 6 or between pH 6 and pH 7, its position varying with the method of fixation and of applying the buffer solutions. It was further observed that between pH 5 and pH 7 there were always more pronounced metachromatic effects than with either more acid or more alkaline buffer solutions.     

Investigation of Thiazin Dyes as Biological Stains II. Influence of Buffered Solutions on Staining Properties

The effect of buffer solutions of varying reaction upon staining fixed sections with thionin, azures A, B, and C, and methylene blue has been studied. The buffer solutions were employed in one of three different ways: for pre-treatment of the sections, for post-treatment, or as solvents for the dyes. Regardless of the method of employing the buffer solutions it was found that the intensity of staining increased with increasing pH-values (a fact which is generally known to be true in the case of basic dyes). It is not certain whether this effect is due to varying the H-ion concentration or to altering the salt content of the solution, or to both. It was also noticed that there was one point where the staining intensify increased most rapidly. This point was either between pH 5 and pH 6 or between pH 6 and pH 7, its position varying with the method of fixation and of applying the buffer solutions. It was further observed that between pH 5 and pH 7 there were always more pronounced metachromatic effects than with either more acid or more alkaline buffer solutions.     

Microspectrophotometric Analysis of Accumulation of the Fluorones K-Fluorescein, Rose Bengal and Phloxine Red in Living Plant Cells

Spectrophotometry investigations of dye solutions in different media and of living stained cells from the upper epidermis of the scaleleaf of Allium cepa were carried out with the dyes K-fluorescein, rose Bengal and phloxine red to elucidate the mechanism of the accumulation of these dyes in the cytoplasm, the nucleus and the cell sap. Thin layer chromatography and paper electrophoresis indicate that the K-fluorescein used here contains no detectable contaminants. Besides the main component, rose Bengal contains two components in small quantities with Rf values of 0.64 and 0.57, plus three more components in traces. Besides the two main components (Rf values of 0.83 and 0.73), phloxine red also contains five more components in traces. Electrophoretic investigations reveal that in aqueous solution the fluorones rose Bengal and phloxine red from pH 2.0-11 show a migration toward the anode. K-fluorescein from pH 2.9-10.4 shows a migration toward the anode, but at pH 1.9 a migration toward the cathode. By shaking aqueous solutions of K-fluorescein, rose Bengal and phloxine red at different pH values with different organic solvents, the above used stainings show different spectral absorption curves according to the polarity of the solvent. The position of the absorption maxima and the shape of the absorption curves of these three anionic dyes lead to the conclusion that the staining of the living cytoplasm and nucleus is due to ion accumulation by means of the “ion trap mechanism” within the aqueous phase of the cytoplasm (cytosol) and the nucleus. Adsorption of dye particles in the protein phase of the cytoplasm cannot be excluded. There seems to be a fundamental difference in the vital staining of the protoplasm by anionic and cationic dyes, the latter apparently accumulating as neutral dye molecules in the lipid phase of the protoplasm. The concentration of the dyes used in the living cytoplasm (cytosol) is approximately 0.2-0.05%. During natural and artificial displacement of K-fluorescein from the cytoplasm to the vacuole, it appears that accumulation of the dye within the vacuole is performed through an ion trap mechanism in the form of bivalent ions. Along with natural displacement, it is possible that ion accumulation also occurs in metabolic products.     

ISOELECTRIC POINTS FOR THE MYCELIUM OF FUNGI

1. Mycelium of Rhizopus nigricans when stained with certain acid and basic dyes and washed with buffer mixtures of 0.1 M phosphoric acid and sodium hydroxide responded much like an amphoteric colloid with an isoelectric point near pH 5.0. 2. When grown on potato dextrose agar the reaction of which was varied with phosphoric acid the extent of colony growth of Rhizopus nigricans plotted against the initial Sörensen value of the agar produced a double maximum curve with the minimum between the two maxima at initial pH 5.2. 3. When grown in potato dextrose broth the reaction of which was varied with phosphoric acid the dry matter produced by Rhizopus nigricans plotted against the Sörensen value of the broth produced a double maximum curve with the minimum between the two maxima at initial pH 5.2 or average pH 4.9. 4. Mycelium of Rhizopus nigricans placed in buffer mixtures of 0.01 M phosphoric acid and sodium hydroxide of pH 4.1 to 6.3, changed the reaction in most cases toward greater alkalinity. 5. Mycelium of Fusarium lycopersici stained with certain acid and basic dyes and washed with buffer mixtures of 0.1 M phosphoric acid and sodium hydroxide responded much like an amphoteric colloid with an isoelectric point near pH 5.5.     

On the possibility of applying noncovalent dyes for protein labeling in isoelectric focusing

Noncovalent fluorescent dyes are widely used for protein quantification and postcolumn detection in electrophoretic separations and recently some attempts to separate the precolumn labeled proteins using isoelectric focusing (IEF) have been made. In the present study, the possibility of applying the technique of protein labeling with noncovalent dyes for IEF is investigated. We found that fluorescent signal emitted by NanoOrange dye increases essentially in presence of carrier ampholyte (CA) components, which makes problematic a reliable protein detection in CA environment. Since in an isoelectric focusing mode the CA species are present in much greater concentration than the concentrations of fractionated proteins, the method of protein labeling with NanoOrange is not suitable for precolumn labeling and cannot be used for CA-IEF, at least without more detailed study of the dye-protein interaction mechanism.     

Fluorescence and viability of Proteus mirabilis stained directly with fluorescein isothiocyanate

Grunberg, E. (Hoffman-La Roche, Inc., Nutley, N.J.), and R. Cleeland. Fluorescence and viability of Proteus mirabilis stained directly with fluorescein isothiocyanate. J. Bacteriol. 92:23-27. 1966.-Washed cell suspensions of Proteus mirabilis, under the proper conditions, stained well with fluorescein isothiocyanate with little or no loss of cell viability. The speed and intensity of the reaction was dependent on both the concentration of dye and pH. Within a range of pH 3.0 to 10.0, staining was most rapid at pH 5.0 to 6.0, with a slower and less intense reaction occurring at the other pH values. As the concentration of dye at either pH 5.0 or 9.0 was increased from 10 to 1,000 mug/ml, there was an increase in the rate of staining but a decrease in cell viability. After 24 hr of incubation at 4 C, pH 5.0, and a dye concentration of 10 mug/ml, all cells were stained, the majority exhibiting intense fluorescence with little or no loss of viability noted. In preliminary experiments with Staphylococcus aureus, similar results were obtained. Of various other fluorescent dyes tested, only rhodamine isothiocyanate was found to give satisfactory staining.     

Mechanism of connective tissue techniques I. The effect of dye concentration and staining time on anionic dye procedures

Summary Anionic dye connective tissue procedures were performed by staining for 5 min and 24 h with (a) 0.00018m and 0.0018m solutions of 28 dyes, and 0.018m solutions of 21 dyes in saturated picric acid (SPA), and (b) 0.0018m and 0.018m solutions of 20 dyes in 1% (w/v) phosphomolybdic acid (PMA). The staining obtained with dyes in SPA was classified as selective (no cytoplasmic staining), moderately selective (traces of cytoplasmic staining) and non-selective (all other staining patterns). The staining of collagen and cytoplasm with dyes in PMA was separately classified on a scale of 1–5 (1 = no staining, 5 = maximum staining). The selectivity of the staining obtained with SPA with solutions of dyes at concentrations of 0.00018m and 0.0018m, and both staining times, was correlated (p < 0.001) with an empirical sulphonic acid constant (SAC) defined as the (number of dye sulphonic acid groups/dye molecular weight) × 10³. Correlation with molecular weight was poor and was significant only when staining was performed with 0.00018m dye solutions for 24 h. The dyes were divisible into three groups: group 1 (selectivity independent, or almost independent of staining time), group 2 (selective to moderately selective when staining was performed for 5 min), and group 3 (non-selective). The SAC of the group 1 dyes differed significantly from those of the group 2 and 3 dyes. Selectivity was essentially lost at dye concentrations of 0.018m. The staining with acidic dyes (no amines or substituted amines) in PMA differed significantly (p < 0.001) from that obtained with amphoteric dyes (containing basic substituents). In general, acidic dyes stained cytoplasm. Amphoteric dyes with the exception of indigocarmine stained collagen. However, most of these dyes also stained cytoplasm. In contrast to the results obtained with dyes in SPA, selectivity correlated strongly with molecular weight and only poorly with the SAC. Staining time and dye concentration affected selectivity only when the acidic dyes were used for 5 min at concentrations of 0.0018m and 0.018m. The data obtained do not permit a clear distinction between the rate control and chemical affinity models for the mechanism of staining with anionic dyes. However, it seems possible that different groups of dyes stain by different mechanisms. Part of this work was performed by M.I., S.N., M.J. and L.M. in partial fulfilment of the requirements for the completion of Pathology 438. A partial account of this work was presented at the annual convention of the British Columbia Society of Medical Technology, Victoria, British Columbia, October 1991.     

The reaction between some dyes and synthetic hydroxyapatite 2. Nature of the binding reaction

Synopsis In order to study the reactions involved in some of the histochemical procedures used for demonstrating calcium in calcified tissues, it was considered appropriate to use well characterized synthetic hydroxyapatite in the first instance. In the first paper of this series (Speirs, 1970), it was found that many dyes not previously used in histochemistry were capable of staining hydroxyapatite; the purpose of the present paper is to describe the numerous experimental approaches that have been made in an attempt to elucidate the mechanisms involved in the adsorption of some of these dyes by hydroxyapatite. Dyes have been grouped according to their adsorption curves (in which dye uptake by solid was plotted against the concentration of dye in solution at equilibrium). From these graphs, predictions and calculations were made concerning the orientation of the dye molecules on the surface of hydroxyapatite, the type of bonding possibly involved and the area of surface covered by each molecule. These were then related to the dimensions and structure of the dye molecules. Saturation of surface sites was achieved in the adsorption of some dyes and the nature of these sites was investigated by studying (1) competition between several dyes for the surface, (2) the accessibility of surface calcium and phosphorus in stained and unstained hydroxyapatite, and (3) the release of³²P from surface labelled hydroxyapatite during dye adsorption. Most of the dyes adsorbed from 95% ethanol were displaced relatively easily by treatment with 0.5 mM phosphate in ethanol, but those adsorbed from tris buffer, pH 7.45, were more stable when exposed to phosphate in tris. Treatment of stained hydroxyapatite with solvents containing 0.5 mM calcium reduced the rate of elution of the dyes. Convincing evidence for chelation, hydrogen bonding, ion exchange and physical adsorption processes as the mechanisms of adsorption has not been obtained. Future studies to investigate these processes are discussed.     

Reactions of Hemoglobiniferous Cells to Aced and Basic Dyes under Varying Conditions of H-Ion Activity

1. An attempt has been made to apply Loeb's concept of the amphoteric nature of proteins for the discrimination of suspected hemoglobiniferous substances from known hemoglobiniferous substances according to their reactions to acid and basic dyes with reference to the isoelectric point of hemoglobin (pH 6.8).

2. The substances in the cytoplasm of known hemoglobiniferous cells (red blood corpuscles, normoblasts and erythroblasts) of the lymph nodes, spleen and bone marrow of the albino rat, when suspended in buffered dye-sucrose solutions, retain eosin on the acid side of pH 7.0, but the substances of the Russell bodies, suspected of being hemoglobiniferous, do not retain eosin at all; and the cytoplasm of the plasma cells, also alleged to be slightly hemoglobiniferous, only retains eosin on the acid side of pH 6.4.

3. The only basic dye used which did not precipitate in buffer solutions was methylene blue. This did not react with hemoglobin in accordance with Loeb's concept, because it did not penetrate mature red blood corpuscles and in those immature erythrocytes which it did penetrate it was precipitated by the reticulum.

4. Therefore, from the results obtained with the acid dye, it is tentatively concluded that the substance in the Russell bodies and in the cytoplasm of the plasma cells are not hemoglobiniferous because they do not react as do the substances in known hemoglobiniferous cells with reference to the isoelectric point of hemoglobin.

5. More investigation, however, must be carried out on both fresh and fixed material before a final unequivocal answer can be made to this problem.     

Standard specimens for stain calibration and their application to the Papanicolaou stain

Standardized specimens composed of extracts of biologic objects (nucleoprotamine and bovine liver) were developed as tools for the quantitative evaluation of stain performance on biologic substrates. The specimens are mixtures of proteins and nucleic acids and thus mimic the staining characteristics of cytologic smears. The concentration of each mixture and the specimen thickness can be precisely controlled, ensuring the production of a large number of samples with a nearly identical capability for dye binding. The transmitted light spectra of the standardized specimens varied depending on the extract and the preparation conditions. Spectra similar to those reported from the nuclei and cytoplasm of cell types in Papanicolaou-stained cervicovaginal smears were observed. Light transmission was uniform to +/- 5% across each specimen and from specimen to specimen. The specimen thickness was uniform within +/- 2%. Studies with these standardized samples could reveal the much-needed correlations between the chemical and optical characteristics of dyes and dye solutions and the performance of the dyes on biologic substrates.     

Reactions of Hemoglobiniferous Cells to Aced and Basic Dyes under Varying Conditions of H-Ion Activity

1. An attempt has been made to apply Loeb's concept of the amphoteric nature of proteins for the discrimination of suspected hemoglobiniferous substances from known hemoglobiniferous substances according to their reactions to acid and basic dyes with reference to the isoelectric point of hemoglobin (pH 6.8).

2. The substances in the cytoplasm of known hemoglobiniferous cells (red blood corpuscles, normoblasts and erythroblasts) of the lymph nodes, spleen and bone marrow of the albino rat, when suspended in buffered dye-sucrose solutions, retain eosin on the acid side of pH 7.0, but the substances of the Russell bodies, suspected of being hemoglobiniferous, do not retain eosin at all; and the cytoplasm of the plasma cells, also alleged to be slightly hemoglobiniferous, only retains eosin on the acid side of pH 6.4.

3. The only basic dye used which did not precipitate in buffer solutions was methylene blue. This did not react with hemoglobin in accordance with Loeb's concept, because it did not penetrate mature red blood corpuscles and in those immature erythrocytes which it did penetrate it was precipitated by the reticulum.

4. Therefore, from the results obtained with the acid dye, it is tentatively concluded that the substance in the Russell bodies and in the cytoplasm of the plasma cells are not hemoglobiniferous because they do not react as do the substances in known hemoglobiniferous cells with reference to the isoelectric point of hemoglobin.

5. More investigation, however, must be carried out on both fresh and fixed material before a final unequivocal answer can be made to this problem.     

Optimization of staining conditions for microalgae with three lipophilic dyes to reduce precipitation and fluorescence variability

When the fluorescence signal of a dye is being quantified, the staining protocol is an important factor in ensuring accuracy and reproducibility. Increasingly, lipophilic dyes are being used to quantify cellular lipids in microalgae. However, there is little discussion about the sensitivity of these dyes to staining conditions. To address this, microalgae were stained with either the lipophilic dyes often used for lipid quantification (Nile Red and BODIPY) or a lipophilic dye commonly used to stain neuronal cell membranes (DiO), and fluorescence was measured using flow cytometry. The concentration of the cells being stained was found not to affect the fluorescence. Conversely, the concentration of dye significantly affected the fluorescence intensity from either insufficient saturation of the cellular lipids or formation of dye precipitate. Precipitates of all three dyes were detected as events by flow cytometry and fluoresced at a similar intensity as the chlorophyll in the microalgae. Prevention of precipitate formation is, therefore, critical to ensure accurate fluorescence measurement with these dyes. It was also observed that the presence of organic solvents, such as acetone and dimethyl sulfoxide (DMSO), were not required to increase penetration of the dyes into cells and that the presence of these solvents resulted in increased cellular debris. Thus, staining conditions affected the fluorescence of all three lipophilic dyes, but Nile Red was found to have a stable fluorescence intensity that was unaffected by the broadest range of conditions and could be correlated to cellular lipid content.     

Drimarene brilliant blue--a better pre-stain in protein separation and visualization.

Prestaining of human serum proteins with a new reactive dye Drimarene Brilliant Blue (DBB), was standardized employing 940 separations and examining 30 variables. Under the critical condition, the serum and the soluble dye (0.1 g/100 ml in working Tris-glycine buffer, pH, 8.3), was mixed in equal proportion, conjugate warmed at 40 degrees C for 2 hr and a 30 microliter of the sample electrophoresed by disc electrophoresis. The method when compared with prestaining by Remazol Brilliant Blue (RBB) and postelectrophoretic staining by Amido Black (AB) in 50 normal sera, revealed that the discs stained with DBB were intense and well defined and appeared in 2 hr on a sparkingly clear gel. Quality of resolution was better than RBB and AB. Protein bands eluted from the DBB prestained gels retained their immunoreactivity. The dye-protein complex of albumin and transferrin produced high-titre monospecific antisera in rabbits.     

A Comparative Study of Several Samples of Neutral Rep and Their Effects on Paramoecium Caudatum

Several samples of neutral red have been studied; first, for the determination of their relative color intensities, and second, to determine their toxic effects on Paramoecium caudatum.

It was found that each of these dyes varied in physical characters both in dry form and in solution. The duration of life of groups of Paramoecia varied in each dye solution. These differences are probably due, at least in part, to differences in the chemical composition of each dye. This suggests that the varying results obtained by experimenters, in staining living material when using the same kind of dye under uniform conditions, may probably be attributed to these differences of chemical constitution of the dyes.

In the comparison of the toxic effects of the several samples most uniform results were obtained at concentrations of 1:5,000 and 1:10-000. At a concentration of 1:100,000 neutral red was found toxic but the results obtained were not in agreement with those obtained at lower concentrations.     

A Comparative Study of Several Samples of Neutral Rep and Their Effects on Paramoecium Caudatum

Several samples of neutral red have been studied; first, for the determination of their relative color intensities, and second, to determine their toxic effects on Paramoecium caudatum.

It was found that each of these dyes varied in physical characters both in dry form and in solution. The duration of life of groups of Paramoecia varied in each dye solution. These differences are probably due, at least in part, to differences in the chemical composition of each dye. This suggests that the varying results obtained by experimenters, in staining living material when using the same kind of dye under uniform conditions, may probably be attributed to these differences of chemical constitution of the dyes.

In the comparison of the toxic effects of the several samples most uniform results were obtained at concentrations of 1:5,000 and 1:10-000. At a concentration of 1:100,000 neutral red was found toxic but the results obtained were not in agreement with those obtained at lower concentrations.     

Mechanisms of Giemsa banding

Summary We investigated the capability of individual thiazins in Giemsa mixtures (methylene blue and azures A, B, and C) and of two related dyes (toluidine blue and thionin) to produce G-banding. We further tested the effects of variations of buffer composition and concentration, dye concentration, and staining time.G-banding was produced by all of the dyes at low concentrations, although differences were noted. Overall, methylene blue and azure B produced the best banding, azures A, C, and toluidine blue produced moderately good banding, and thionin produced poor banding. This order did not appear to be altered essentially by different treatments. The optimal conditions for G-banding for all dyes and treatments included the use of (1) 0.025–0.05M phosphate buffer, (2) dye concentrations of 0.002%–0.005%, and (3) staining times of 6–15 min.     

Victoria blue B--a nuclear stain for cytology. A cytophotometric study

The aim of this study was to investigate the staining characteristics of Victoria Blue B in alcohol solutions. Cytological specimens (liver and spleen tissue imprints, blood smears) were stained with methanol solutions of commercially available Victoria Blue B-Cl and with pure Victoria Blue B-BF4. The dye concentration, staining time, and protone concentration of the dye solution were varied. The dye solutions were characterized using spectrophotometry and thin-layer chromatography. Cytophotometry and image analysis were used to quantitate the staining pattern of cell nuclei. Feulgen-stained slides were used as controls. Victoria Blue B-BF4 gave excellent nuclear staining exhibiting a quantitative dye-substrate relationship, whereas commercial dyes resulted in lower staining intensity and less distinct nuclear texture. Dye concentration and staining time were, over wide ranges, not of critical importance for the quality of the staining. Under certain staining conditions, only cell nuclei were stained, with the background remaining completely unstained. We presume that, in alcohol solutions, Victoria Blue dye binds as a neutral dye molecule in conjunction with its anion. Victoria Blue B-BF4 staining provides a simple and reproducible staining technique for cytology which is suitable for use in automated cell-pattern recognition.