Cleared Whole Mounts of Shoot Apices of Angiosperms for Topographic Study

Cleared and stained whole mounts of stem apices of two Labiates and of Phaseolus plumule giving a three-dimensional picture of the apical structure have been prepared as follows. Fix the buds in formalin-acetic acid-50% alcohol (5:5:90) for 24 hr or longer and then dissect under a binocular microscope to leave only the youngest leaves surrounding the apex. Wash for several minutes in distilled water and then clear the material in a 5% solution of sodium hydroxide at approximately 40° C for 24-48 hr. Wash thoroughly in several changes of distilled water, transfer to a solution of 1% tannic acid and 0.5% sodium salicylate for up to a minute. Wash briefly in distilled water and stain in a 1.5% solution of ferric chloride until blue-black. Wash in distilled water and dehydrate through 50%, 70%, 85%, 95% and 2 changes of absolute ethyl alcohol. If the xylem is not stained well, counter-stain for a few seconds in a 0.5% solution of safranin O in a 1:1 mixture of xylene and absolute alcohol and wash out the excess stain in the same mixture. Clear in 2 changes of xylene and place on a glass slide in thick Canada balsam. Orient with needles under low magnification and cover.     

Safranin and Anilin Blue with Delafield's Hematoxylin for Staining Cell Walls in Shoot Apexes

The following technic is suggested for staining cell walls in shoot apexes: After the usual preliminary steps through 50% ethyl alcohol, stain in 1 % safranin 0 for 24 hours. Rinse in tap water and place in 2% aqueous tannic acid for 2 minutes. After rinsing in tap water, stain for 2 minutes in 1 part Delafield's hematoxylin to 2 parts distilled water and rinse in tap water. Remove excess hematoxylin with acidified water (1 drop cone. HC1 in 200 ml. water), then place slides in 0.5% lithium carbonate for 5 minutes. Dehydrate through an ethyl alcohol series, then transfer from absolute alcohol to a saturated solution of anilin blue in “methyl cellosolve” for 5-10 minutes. Wash in absolute alcohol, rinse in a solution of 25% methyl salicylate, 33% xylene, 42% absolute ethyl alcohol and clear for 10 minutes in a solution of 2 parts methyl salicylate, 1 part xylene, 1 part absolute ethyl alcohol. Transfer through two changes of xylene and mount in “clarite” or suitable alternate. The resulting preparations will have clearly defined, dark-staining cell walls and will photograph well when “Super Panchro-Press, Type B” film (Eastman Kodak Co.) is used in conjunction with suitable Wratten filters.     

Safranin and Anilin Blue with Delafield's Hematoxylin for Staining Cell Walls in Shoot Apexes

The following technic is suggested for staining cell walls in shoot apexes: After the usual preliminary steps through 50% ethyl alcohol, stain in 1 % safranin 0 for 24 hours. Rinse in tap water and place in 2% aqueous tannic acid for 2 minutes. After rinsing in tap water, stain for 2 minutes in 1 part Delafield's hematoxylin to 2 parts distilled water and rinse in tap water. Remove excess hematoxylin with acidified water (1 drop cone. HC1 in 200 ml. water), then place slides in 0.5% lithium carbonate for 5 minutes. Dehydrate through an ethyl alcohol series, then transfer from absolute alcohol to a saturated solution of anilin blue in “methyl cellosolve” for 5-10 minutes. Wash in absolute alcohol, rinse in a solution of 25% methyl salicylate, 33% xylene, 42% absolute ethyl alcohol and clear for 10 minutes in a solution of 2 parts methyl salicylate, 1 part xylene, 1 part absolute ethyl alcohol. Transfer through two changes of xylene and mount in “clarite” or suitable alternate. The resulting preparations will have clearly defined, dark-staining cell walls and will photograph well when “Super Panchro-Press, Type B” film (Eastman Kodak Co.) is used in conjunction with suitable Wratten filters.     

A Controllable Differential Stain for the Hypophysis by Adaptation of the Mallory Triple Stain

A selective and controllable staining method for the hypophysis has been developed with rat material, using Mallory's triple stain as a basis.

Fix in Zenker neutral formol for 6 hours. Longer fixation is undesirable. Transfer to 30% alcohol plus a few drops of a saturated solution of I₂ in aqueous KI over night. Gradually complete dehydration and clear in cedar oil. Infiltrate with a paraffin mixture (paraffin, rubber-paraffin, bayberry wax and beeswax). Section 3-Sμ. Hydrate to distilled water, placing a few drops of a KI-I₂ solution in the 50% alcohol. Stain in 1% acid fuchsia for 30 minutes. Rinse, and differentiate in a weak NH₄OH solution (one drop 28% NH₄OH to 200 cc. HOH). When differentiation is complete, transfer to a 0.5% phosphomolybdic acid solution for 3 minutes, after first stopping the differentiation with a 0.1% HC1 solution and then rinsing with distilled water. Stain for one hour in a solution of: 1% anilin blue, water soluble, 2% orange 6, and 1% phosphomolybdic acid. Rinse in distilled water plus a few cubic centimeters of the stain. Differentiate in 95% alcohol, transfer to absolute alcohol and clear in a mixture of 30% oil of cedar, 40% oil of thyme, 15% absolute alcohol and 15% xylene. Finally, transfer to xylene and mount.     

A Universal Stain for the Sex Chromatin Body

For the demonstration of the sex chromatin body in human tissues, fixation in 95% alcohol or modified Davidson's solution (95% alcohol, 30; formalin, 20; glacial acetic acid, 10; distilled water, 30) was best. The staining procedure chosen for most materials is the following: Mounted preparations are coated with celloidin, hydrated, hydrolyzed 20 min in 52V HCl at 20-25°C, rinsed thoroughly in several changes of distilled water and transferred to a buffered thionin solution. This consists of 3 parts: (1) A saturated solution of thionin in 50% alcohol (filtered); (2) Michaelis buffer: sodium acetate (3 H₂O), 9.714 gm; sodium barbiturate, 14.714 gm; CO₂-free distilled water, 500 ml; and (3) 0.1N HCl. To make the staining solution, mix 28.0 ml of the buffer solution with 32.0 ml of 0.1N HCl and bring the total volume to 100.0 ml with the thionin solution. Its pH should be 5.7 × 0.2, and care should be exercised that no acid is carried over from the hydrolyzing solution, since this would progressively lower the pH. The staining time varies from 15 to 60 min, depending on the specimen, but the shortest time consistent with adequate staining gives the clearest preparations. Slides are rinsed in distilled water and 50% alcohol and allowed to remain in 70% alcohol until the heavy clouds of stain cease to appear. Differentiation is completed in 80% and 95% alcohol, followed by dehydration in absolute alcohol, clearing in xylene and applying a cover glass with a synthetic resin (G. T. Gurr's DePeX was used). The sex chromatin is deep blue-violet and sharply contrasted against the lightly colored particulate chromatin of the nucleus. Cytoplasm remains unstained but fibrin and related structures show metachromasia. Chromosomes are well demonstrated if present. The method works on all types of tissues, is simpler and quicker than the Feulgen method, and often yields superior results.     

Haematoxylin-Phloxine-Alcian Blue-Orange G Differential Staining of Prekeratin, Keratin and Mucin

This is a modification of Kreyberg's stain with Alcian blue 8GS used to stain acid much while phloxine B and orange G stain keratin and prekeratin. Procedure: Dewax formalin-fixed paraffin sections in xylene and hydrate through alcohol. Stain in Mayer's haemalum, 10 min; blue in tap water; wash in distilled water; stain in 1% phloxine, 3 min; wash in running water, 1 min; wash in distilled water; stain in 0.5% aqueous Alcian blue in 0.5 acetic acid, 5 min; wash in distilled water; stain in 0.5% orange G dissolved in 2.0% phosphotungstic acid, 13 min; dehydrate quickly in 2 changes of 95% alcohol and 2 changes of absolute alcohol; clear in several changes of xylene; mount in a synthetic resin. Acid mucopolysaccharides are stained turquois blue; prekeratin and keratin are orange to red orange.     

A Tetrachrome Stain for Fresh, Mineralized Bone Sections, Useful in the Diagnosis of Bone Diseases

Fresh, unprocessed bone is ground to sections 75-100 μ thick, stained in an aqueous solution composed of fast green FCF, 0.1 gm; orange G, 2.0 gm; distilled water, 100.0 ml; and adjusted to pH 6.65, then in a mixture of 1 part alcoholic solution of 0.25% celestine blue B and 9 parts of alcoholic solution of 0.1% basic fuchsin. Surface stain is removed by grinding sections to 50 μ and washing them in 1% invert soap (Zephiran) to remove adherent debris. (Commercial detergents and alkaline soaps may interfere with chromophore groups of the dyes.) Wash in tap water; rinse in distilled water and differentiate in 1% acetic alcohol. Dehydrate in ascending alcohols, clear in xylene and mount permanently in a neutral, synthetic resin. Active osteoid seams stain dark to light green; resting osteoid seams, red to bright orange red; transitional osteoid seams, geenish-yellow, orange red to red; older, partly mineralized matrix, orange; new, partly mineralized matrix, red; osteocyte nuclei, red; osteoblasts and osteoclasts, greenish-blue to dark purple nuclei and green or light green cytoplasm. Hyper-trophic and differentiating cartilage cells are stained light pink and dark red respectively. The staining reactions are consistent; the solutions are stable.     

Carbol Fuchsin as A Stain for Human Chromosomes

Cells derived from cultures of bone marrow or leucocytes were treated with hypotonic citrate solution, squashed in 45% acetic acid frozen with CO₂ to allow removal of the cover glass without disturbing the smear, and stained by the following schedule: absolute alcohol, 5 min; coat with 0.2% parlodion and air dry; 70% alcohol, 5 min; distilled water, 5 min; stain 2-5 min in a mixture of 45 ml of a 0.3% solution of basic fuchsin in 5% phenol, 6 ml of glacial acetic acid, and 6 ml of 37% formaldehyde. Differentiate and dehydrate in absolute alcohol, clear in xylene and cover. The stain is durable for several weeks if slides are stored in darkness when not in use. Results resemble those obtained by Feulgen or aceto-orcein methods.     

Staining Procedures for Ultrathin Sections of Tissues Embedded in Polyester Resin

Tissues were fixed for 30 min In cold (0-2° C) 1% OsO₄ (Palade) buffered at pH 7.7, to which 0.1% MgCl₂ was added. Dehydration was in a graded ethanol series (containing 0.5% MgCl₂) at 0-2° C, and terminated with 2 changes of absolute ethanol. Tissues were then transferred by a graded series to anhydrous acetone. Infiltration of the tissue with Vestopal-W (a polyester resin), is gradual with the aid of graded solutions of Vestopal-W in acetone. The infiltrated tissue is encapsulated and initial polymerization is done under ultraviolet light at room temperature for 8-16 hr. This is followed by final hardening at 60° C for 36-48 hr. Sections (0.2-1 μ) were cut, dried on slides, placed in acetone for 1 min and then treated by either of the following staining procedures: (1) Thionin-azure-fuchsin staining: Flood the preparation with 0.2% aqueous thionin and heat to 60-80° C for 3 min; if the preparation begins to dry, add stain. Rinse in distilled water. Flood the slide with 0.2% azure B in phosphate buffer at pH 9. Heat to 60-80° C for 3 min; do not permit the preparation to dry. Rinse in distilled water. Dip the slide in MacCallum's variant of Goodpasture's carbol-fuchsin stain for 1-2 sec. Rinse in distilled water. Check the preparation microscopically for intensity of the fuchsin stain. Repeat dips as may be needed to obtain the desired intensity. Rinse in distilled water. Dehydrate quickly in 95% and absolute alcohol; clear in 2 changes of xylene and cover in Permount or similar synthetic resin. (2) Thionin-azure counterstain for the periodic acid-Schiff reaction: Oxidize the tissue in 0.5% periodic acid for 15 min and transfer to Schiff's leucofuchsin solution for 30 min. Counterstain with 0.5% aqueous thionin for 3 min; wash in distilled water; stain in 0.2% azure B in phosphate buffer at pH 5.5; wash in distilled water; dehydrate; clear and cover as in the first method. For temporary preparations let dry after absolute alcohol and apply a drop of immersion oil directly on the section.     

Orcein-Hematoxylin in Iodized Ferric Chloride as a Stain for Elastic Fibers, With Metanil Yellow Counterstaining

Autopsy and biopsy specimens of human skin were fixed overnight in alcoholic Bouin's solution, embedded in paraffin, cut at 7 μ, deparaffinized, hydrated to 70% alcohol, and treated as follows—stained 2 hours in a mixture consisting of: 0.2% orcein in 70% alcohol and 1% HC1 (conc.), 125 ml; 5% hematoxylin in absolute alcohol, 40 ml; 6% FeCl₃ in water, 25 ml; and aqueous I₂-KI (1:2:100), 25 ml—rinsed in distilled water until the excess stain was removed—differentiated in 1.2% FeCl₃, 5-15 sec—washed in running water, 5 min—differentiation completed in 0.01% HC1 acid-alcohol, 1 min—a dip in 95% alcohol—distilled water, 2 min—0.25% aqueous metanil yellow, 5-10 sec—a 95% alcohol dip—dehydrated in absolute alcohol, xylene, and mounted in a resinous medium. The technic combines the orcein of Pinkus' stain and the hematoxylin mixture of Verhoeff into a single staining solution and gives sharp and reliable results for both coarse and extremely delicate elastic fibers. These stain purple; nuclei, violet; and background, yellow. The stain allows the use of formalin, Bouin's fluid and Zenker-formol fixation. The results have been consistent in other primates as well as in man.     

Differential Staining Of Tissue In The Block With Picric Acid And The Feulgen Reaction

The authors have found a modification of the Feulgen reaction to be a satisfactory stain for tissue in the block.

Pieces of fresh mammalian tissue not thicker than 5 mm. are fixed for approximately 48 hours at 25° C. in a mixture of equal parts of 5% aqueous sulfosalicylic acid and saturated aqueous picric acid. They are washed for 30 minutes in three ten-minute changes of distilled water and placed in Feulgen's staining solution diluted to one-half strength with distilled water. The staining solution is allowed to act for 24 hours (2 to 3 mm. thick blocks) up to 48 hours for 5 mm. thickness. After staining, the specimens are transferred to a mixture of sodium bisulfite, 0.5 g. and N hydrochloric acid, 5 ml. in' 100 ml. of distilled water. Two changes of IS to 30 min. each in the acid sulfite are given and these are followed by dehydration through 50%, 70% and 95% alcohol. One to two hours are allowed for each change except the last 95%, in which the stained tissue is allowed to remain overnight. The dehydration is completed in two changes of absolute alcohol with subsequent clearing in xylene and embedding in paraffin. Sections may be cut 10 μ or other thickness desired, mounted on slides, paraffin removed, and covered in the usual manner. Nuclei stain reddish violet against a lemon yellow background when the stain is typical. Orange G, 200 mg. per 100 ml. may be added to the fixing fluid if a more polychromatic effect is desired.     

Maxilon Blue Rl: A New Metachromatic Monoazo Dye

Maxilon blue RL, a basic monoazo dye developed by Geigy S. A., stains metachromatically acid mucopolysaccharide-containing elements in histological sections. This property is due to a chromatographically pure blue fraction which is the main component of the dye. The following routine has been developed for staining sections of formalin-calcium fixed paraffin-embedded tissues. Dewax in xylene and hydrate the sections through alcohol; stain in 0.05% aqueous Maxilon blue RL, from 30-60 sec; wash in distilled water; dehydrate either in tertiary butanol, 2 to 3 min, after removing excess water from the slide by blotting; or, rinse in 70% ethyl alcohol and dehydrate in 2 changes, 2 min each, of absolute alcohol; clear in xylene; mount in DPX or in Canada balsam. Acid mucopolysaccharides are colored red to violet; other basophilic elements, blue.     

Stain Technology a Bone Stain for Osteoid Seams in Fresh, Unembedded, Mineralized Bone

Fresh, ground, mineralized bone sections 75-100 μ thick are stained 90 minutes or 48 hours in the Bone Stain, a preparation containing fast green FCF, orange G, basic fuchsin, and azure II. Surface stain is then removed by grinding under running water. Sections are washed in 0.1% zephiran chloride (benzalkonium chloride) or in 0.01% mild soap and again washed in tap water, followed with distilled water. Sections are next differentiated in 0.01% acetic acid in 95% methanol, dehydrated in 95% ethanol and 100% ethanol, cleared in alcohol:xylene 1:1, 1:4, 1:9 and 2 changes of xylol, and then mounted permanently in Eukitt's mounting media.

Osteoid seams stain either green to jade green or red to dark red, incompletely mineralized bone red or orange yellow, and the zone of demarcation light green. The walls of lacunae, canaliculae, feathered bone, procedural artifacts and periosteocyte lacunar low-density versions stain red.

The method helps in the differential diagnosis of certain metabolic bone diseases in human biopsy and autopsy material.     

Staining Mitochondria in Fixed Blood Smears

Wet blood smears are placed immediately in Helly's fluid for 24 hr, transferred directly to a saturated solution of potassium dichromate for 48 hr and washed in running water for 2-4 hr. The slides are then treated with iodine and sodium thiosulf ate and washed several hours or overnight. Excess water is removed by blotting the slide around the smear, Altmann's aniline fuchsin is placed on the smear and the slide is heated over a spirit lamp until white fumes appear. After the slide cools the stain is poured off and the excess removed by washing with distilled water. Methyl green (1% aqueous) is dropped on the smear and left for approximately 30 sec. It is then passed rapidly through 2 changes of absolute ethanol and into xylene, from which it is mounted in Permount. This stains mitochondria, red blood corpuscles and specific granules of eosinophilic granulocytes red on a green background.     

An Improved Hematoxylin-Eosin Stain for Sections of Marrow Units

The procedure recommended is: Fix “marrow units” (small functional structures of bone marrow) in 10% formol-saline solution for 1-2 hours and dehydrate in 80% alcohol, 95% alcohol and acetone 30 minutes each. Place in fresh 50° and 53°C. paraffin for 30 minutes each. Embed in fresh 53°C. paraffin. Serially section at 5μ thickness and mount with Schleicher's floating solution. Allow to dry for 1 hour in an oven and deparaffinize by passing through xylene I and II, absolute alcohol I and II, and 95% alcohol. Rinse in fresh distilled water and place in dilute Harris' hematoxylin (stock solution 50 ml., distilled water 200 ml.) for 2 to 3 minutes. Rinse well in distilled water and check staining under the microscope. Dip in acid-alcohol 5 times (1 dip to equal about 1 second). Rinse well in weak (0.02%) ammonia water and distilled water. Dip in 2% aqueous phosphotungstic acid about 3 to 5 times (equal to 3-5 seconds). Rinse in fresh distilled water and place in weak ammonia water for 1 minute. Rinse in fresh distilled water I and II. Place in 80% alcohol for 5 minutes and check under the microscope for “blueness” and nuclear differentiation. Place in dilute alcoholic eosin (0.5% alcohol-eosin stock solution 10 parts and 95% alcohol 90 parts) for 1 to 2 minutes. Rinse in 80% alcohol and place for 1 minute in 95% alcohol. Check under the microscope for staining quality. Place in absolute alcohol for 1 minute, alcohol-xylene (equal parts), 10 dips, and xylene I and II. Mount. This hematoxylin-eosin staining schedule brings out minute structural detail of bone marrow tissue heretofore not demonstrable.     

The Use of Bismarck Brown Y in some new Stain Schedules

The staining quality of Bismarck brown Y may be improved and sterility maintained by adding 5% phenol to a 1% aqueous solution. Use the phenolic Bismarck brown in combination with iron alum hematoxylin except for stripped epidermis in the following procedures:

Stem and Root Schedule: Mordant sections from water in 4% iron alum for 10 minutes. Rinse in distilled water and stain in 0.5% aqueous hematoxylin for 1 minute or until darkly stained. Rinse in distilled water and destain in 2% iron alum until a gray color appears. Rinse thoroly in distilled water and intensify hematoxylin by transferring sections to 0.5% aqueous lithium carbonate until the desired black color appears. Rinse thoroly in distilled water and stain for 1-5 minutes in phenolic Bismarck brown. Rinse in distilled water, dehydrate successively in 30, 50, 70, 95 and 100% alcohol. Clear in methyl salicylate for 5 minutes, then to xylene for 3-5 minutes, and mount in balsam.

Middle Lamellae in Wood: Destain more thoroly in 2% iron alum than for the general stem and root schedule, and intensify in lithium carbonate for a longer period (about 1 hour).

White Potato Tuber Sections: Modify above schedule by reducing time of destaining in 2% iron alum to about 30-60 seconds and intensify hematoxylin until starch grains appear bluish in color. Stain in phenolic Bismarck brown for 1-2 minutes.

Wheat Grain Sections: Fix grain for sectioning when in “dough” stage. Use schedule the same as for potato tuber except for reducing time of staining in phenolic Bismarck brown to about 45 seconds.

Tradescantia zebrina Epidermis: Strip epidermis from leaf while submerged in water. Fix in 100% alcohol 10 minutes, pass thru 95, 70, 50, 30, and 10% alcohol to water. Stain in phenolic Bismarck brown for 10-20 minutes. Dehydrate, clear in methyl salicylate and mount in balsam.     

A Buffered Giemsa-Bodian Stain for Neurological Material

A buffered Giemsa counterstain for the Bodian method is described. It is very useful for bringing out Nissl substance and nerve fibers in the same section. Bouin perfused or formalin fixed material from mammals, amphibia, reptiles and fish was used. After fixation, all tissues were decalcified for at least a week in 50% formic acid (1 part) and 20% sodium citrate (1 part). This was washed out thoroughly. The method described by Bodian (1936) was followed except for the following minor changes: Winthrop Protargol (Strong Protein Silver) Batch N346BJ was used exclusively; all glassware was cleaned with acid prior to setting up the stain; before developing, the sections were washed in warm tap water for 10 minutes; the gold chloride was chilled before use. The sections were then put into buffered Giemsa for 24 hours. Stock Giemsa: 0.75 grams powdered Giemsa (Coleman and Bell, Certification No. CGe-3) was dissolved in 50 ml. of glycerin overnight in the oven, then 50 ml. of methyl absolute alcohol were added. To 3 ml. of Giemsa stock solution, 87 ml. of distilled water buffered to pH 5.3 with 10 ml. of Sorensen's buffers were added and the solution filtered. Coleman buffer tablets gave best results at pH 5.0. Sections were then rinsed in 95% alcohol, two changes of absolute alcohol, two changes of xylene, and were then mounted in Clarite.     

Chlorazol Black E as a Stain for Tension Wood

Sections containing gelatinous fibers were cut at 15 μ from material both fixed and stored in formalin-acetic-alcohol, 5:5:90 (of 70%). These sections were stained 5 min in a 1% aqueous solution of lignin pink (G. T. Gurr), differentiated quickly in water, soaked 5 min in 95% ethyl alcohol, dehydrated in absolute ethyl alcohol and counter stained 5 min with a 1% solution of chlorazol black E (G. T. Gurr) in methyl cellosolve, followed by dehydration in absolute ethyl alcohol, clearing in xylene and mounting in Canada balsam. The gelatinous layer was sharply defined as a dense black zone whilst the remainder of the cell wall stained light pink. The specificity of the technique was superior to that of safranin and light green, and was not easily obscured by overstaining. The technique is particularly useful for locating small zones of gelatinous fibres, and for photomicrographical work.     

Staining Cells on a Membrane Filter with Giemsa Stock and Tap Water

Cells grown on type AM 6 Alpha Metricel Gelman filter membranes are fixed 1-2 min with OsO₄ vapor, washed in distilled water, dehydrated 4 min in 95% and 4 min in absolute ethanol. They are then stained for 2 min in a 1:1 dilution of Giemsa stock solution and an approximately neutral, low mineral content tap water. The stain is removed from the filter by 1 min in 50%, 1 min in 95%, 1 min in absolute ethanol and 1 min in a mixture of absolute ethanol and xylene 1:1. The filter is finally cleared in xylene and mounted with a synthetic resin. This procedure gave polychrome staining on neonatal thymic cells from C57 black pedigreed mice and on human leucocytes, with little or no stain retained by the filter membrane.     

A Simplified Nissl Stain with Thionin

Recently two articles on the use of thionin as a cell stain for neurological materials have appeared. One utilizes a solution buffered in the acid range³; the other uses a “steaming” staining solution⁴. For some time we have been using thionin as a routine stain after either formalin or alcohol fixation and our method is so simple and has given such satisfactory results with a variety of brands of thionin that it seemed to be worthy of more general use. Briefly the method consists of placing the celloidin sections in a 0.05% solution of Li₂CO₃ (the percentage of Li₂CO₃ is non-critical) for about 5 minutes and then grossly overstaining in a 0.25% solution of thionin in a 0.05% solution of Li₂CO₃ in distilled water. The overstaining is necessary if all the stain is to be removed from the background. The sections are then passed through distilled water, 70 or 80% alcohol, two changes of butyl alcohol, two changes of xylene and mounted with Clarite. For most material, split mica cover-slips are quite satisfactory. The time of differentiation may be considerably lessened by the use of the differentiator recommended by Neumann (1942) except that we find the chloroform superfluous and transfer the sections to the aniline solution from 95% alcohol. Less fading seems to occur if the aniline differentiator is followed by a saturated solution of Li₂CO₃ in 95% alcohol.