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This simple and reliable 10-min procedure for producing uniformly and intensely stained, as well as fade-resistant, chromosome and sex-chromatin preparations uses pinacyanol chloride as the dye. Slides are extracted in 5 N HC1 at 20-23 C for 2 min, washed in running tap water for 2 min, stained in 0.25% pinacyanol chloride solution (made up in 70% methanol) for 45 sec, differentiated in Wright's buffer solution (pH 6.4-6.5) for 45 sec, washed in running tap water for 5 sec, dehydrated in 2 changes, 1 min each, of absolute tertiary butanol, cleared in 3 changes of xylene, a minimum of 30 sec each, and mounted in a neutral synthetic resin such as Permount.

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 t...